NATIONAL 

SER

Observing 

Handbook No

Marine Surface 

Weather Observations 
p

Radio call sign Call Sign 

YY nth 01-31 

GG Time of observation 00-23 

iw Wind indicator 

LaLaLa Latitude 000-900 

Qc Quadrant 

LoLoLoLo Longitude 0000-1800 

iR Precipitation data indicator 4 

ix r data indicator 

h Cloud base height 

VV 90-99 

N r 

dd Wind direction 

ff Wind speed 00-99 

fff High Speed Wind Knots (099- 

sn Sign of temperature 

TTT Dry bulb temperature Celsius Degree

TdTdTd nt temperature Celsius Degree

PPPP ressure Actual Hp or M

(omit 1 in thous

a 3-hour pressure tendency 0-8 

ppp 3-hour pressure change Hp or Mb 

ww Presen r 00-99 

W1 r (primary) 0-9 

W2 r (secondary) 0-9 

Nh r 

CL Low cloud type 

CM Middle cloud type 

CH High cloud type 

Ds rse 0-9 

Vs rage speed 0-9 

Ss Sign/type sea surface temp. 0-7 

TWTWTW Sea surface temp. Celsius Degree

PWPW Sea period Seconds 

HWHW Sea height Half Meters 

dW1dW1 Primar rection 

dW2dW2 Secondar rection 

PW1PW1 Primar riod Seconds 

HW1HW1 Primar Half Meters 

PW2PW2 Secondar riod Seconds 

HW2HW2 Secondar Half Meters 

Is Ice accretion cause on ship 1-5 

EsEs Ice accretion thickness on ship ntimeters 

Rs Ice accretio ate on ship 0-4 

Sw Sign 0-7 

TbTbTb Celsius Degree

ci Sea ice concentration 

Si nt 

bi Ice of land origin 

Di Ice edge bearing 

zi Ice trend 

p 

D....D 

Day of the mo

3, 4 

1, 3, 5, 7 

Weathe 1, 3 

0-9, / 

Visibility 

Cloud cove 0-9, / 

00-36, 99 

0, 1 

Dew poi

Sea level p

t weathe

Past weathe

Past weathe

Lowest cloud cove 0-9, / 

0-9, / 

0-9, / 

0-9, / 

Ship’s cou

Ship’s ave

y swell di 01-36, 99 

y swell di 01-36, 99, // 

y swell pe

y swell height 

y swell pe

y swell height 

Ce

n r

/type wet bulb temp. 

Wet bulb temp. 

0-9, / 

Sea ice developme 0-9, / 

0-9, / 

0-9, / 

0-9, / 
U.S. DEPARTM E N T OF COMMERCE 

NA

O

N 

National Weather Serv

Observing Handbook N

Marine Surface Weather Observation

July 2004 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Weather Service 

National Data Buoy Center 

Voluntary Observing Ship (VOS) Program 

Building 1100 

Stennis Space Center, MS 39529-6000 
In writing this new edition of NWS Observing Handbook No. 

it has been our intent to include as much useful information 

in the available space. The compact size and design, and “fiel

format, should allow for easy handling and quick reference. W

this simplifies your work as weather observers, and makes it e

locate the information you need. 

Weather has an almost magical hold on the mariner. Every ch

weather at sea is noted with a sense of trepidation. Reporting 

not only contributes to your safety, but adds to your basic kno

seamanship. It is part of keeping a good lookout. 

For every 100 observations on land, there is only about 1 obse

sea. Without your participation in the Voluntary Observing Sh

program, there would be vast marine areas without data, mak

forecasting nearly impossible for these areas. The importance 

reports cannot be overstated. We thank ships officers for thei

dedication, and committment. 

Please follow the weather reporting schedule for ships as best 

(0000, 0600, 1200, 1800 UTC from all areas; every 3-hours fro

Great Lakes, from within 200 miles of the United States and C

coastlines, and from within 300 miles of named tropical storm

hurricanes). For assistance, contact a Port Meteorological Off

(PMO), who will come aboard your vessel and provide all the 

information you need to observe, code, and transmit weather 

(see page 1-3 through 1-6). 

NWSOH No. 1 iii 
Preface iii 

Introduction vii 

2-1 

1-1 Chapter 1: Program Description 

Chapter 2: Ship’s Synoptic Code and 

4-1 

3-1 

Observing Methods 

Chapter 3: Transmitting the Observat

Chapter 4: The Weatherwise Mariner 

5-1 Glossary 

B-1 

A-1 Appendix A: Observing Forms and Su

Appendix B: Conversion Factors and 

Equivalents 

C-1 Appendix C: Interpretation of 

Weather Map Symbols 

D-1 Appendix D: Marine Warning and 

Forecast Areas 

NWSOH No. 1 v 
For beginners and established observers alike, this new edition of th

Weather Service Observing Handbook No. 1 (NWSOH1) explains h

observe, how to code, and how to transmit weather observations fro

ships at sea. 

IMPORTANCE OF OBSERVATIONS FROM SHIPS 

Accomplishments in the atmospheric sciences have their roots in ob

They are a critical first step in the end-to-end forecast process. This 

sists of the taking and coding of observations, the transmission and 

data, the processing and analysis of data (including numerical and 

modeling), followed by the preparation and issuance of forecasts an

More specifically, observations are used by meteorologists to evalua

weather conditions, and to locate and determine the strength of we

tems such as fronts, air masses, high and low pressure systems, trop

and hurricanes. Your observations are especially important in the p

the surface weather chart. Isobars (lines of equal barometric pressu

are crucial for defining and delineating all weather systems, could n

over marine areas without ship reports. 

Ships observations are not only important for weather forecasts at s

for forecasts over land areas, because marine weather systems often 

inland. Notable examples include (1) North Pacific Ocean weather 

which frequently move eastward to effect the weather over much of 

America, especially during the winter season, (2) tropical storms an

canes, which develop over the oceans, and can cause great devastat

highly populated coastal areas, (3) weather systems over the North 

Ocean, which have a great impact on the weather of Europe. 

Accurate marine data is also used to prepare long range forecasts of 

perature, and precipitation, in the monitoring of climatic change, oc

and eddies, and to study the interaction of air and sea. This is import

culture, industrial planning, ship routing, fishing, and many other ac

charts and climatological atlases of the oceans are largely based on o

from ships. Your weather observations will also help you interpret the 

changes in weather that occur at your position or along your route. 

ELEMENTS TO BE OBSERVED 

Ships taking meteorological observations should be familiar with th

for observing or measuring the following elements: 

(1) Cloud height, amount, and type; 

(2) Visibility;

NWSOH No. 1 vii 
(6) Weather - present and past; 

(7) Course and speed of ship;

(8) Sea surface temperature; 

(9) Sea waves and swell - period, direction, and height;

(10) Ice conditions, including icing on board ship;

EQUIPMENT REQUIRED 

Suitable instruments for use on ships are the following: 

(1) Precision aneroid barometer or marine mercury barometer; 

(2) Dry and wet-bulb psychrometer (sling, or housed in an outdoor 

(3) Barograph;

(4) Sea temperature thermometer, either a continuously immersed 

(intake or hull mounted) or sea water bucket; 

An anemometer to measure wind force may be used as an alternative to 

wind estimates using the beaufort scale. 

OBSERVING ORDER 

In general, instrumental observations requiring the use of a light shoul

made after non-instrumental ones, so that eye function in the dark is no

impaired. Efforts should be made to observe elements other than press

within the ten minutes preceeding the reporting hour. Ideally, atmosph

pressure should be read at exactly the standard time. 

HISTORICAL NOTE 

Since the invention of meteorological instruments did not begin until t

seventeenth century, instrumental records of the weather elements cove

more than 200 years anywhere, while for many parts of the world, the p

observation is a good deal less than 100 years. The best records are avai

from well-populated land areas. 

Notable inventions include the air thermometer (Galileo, 1592), alcoho

and mercury thermometer (Fahrenheit, 1714), the mercury barometer 

(Torricelli, 1643), the aneroid barometer (Vidie, 1843), and the anemo

(Hooke, 1667). 

During the eighteenth and nineteenth centuries, mariners began keepi

weather and oceanographic records and logs. Knowledge of prevailing w

and ocean currents came about as a result of these records. The Volunt

Observing Ship (VOS) Program as we know it today is rooted in the wo

Mathew Fontaine Maury, head of the U.S. Navy Hydrographic Office, w

organized a meeting in Brussels in 1853, attended by delegates of ten m

maritime nations. The purpose of the meeting was to discusss the estab

NWSOH No. 1 viii 
In the present century, the VOS program was recognized in 1948 in 

International Convention For The Safety Of Life At Sea (SOLAS): 

The contracting governments undertake to encourage the collection of meteor

by ships at sea and to arrange for their examination, dissemination and exc

manner most suitable for the purpose of aiding navigation. Administration

age the use of instruments of a high degree of accuracy, and shall facilitate 

such instruments upon request. 

HAVE YOUR INSTRUMENTS CALIBRATED AND 

REPORT ACCURATE DATA 

Always ensure that your equipment is accurate and properly calibrated

Meteorological Officer (PMO) should calibrate your barometer and b

once every 3 months, and also check your psychrometer during every 

Sea-water thermometers (whether hull-mounted or located in the con

intake) should be calibrated annually, and checked every time your ve

yard for service. If your vessel has an anemometer, it should be calibra

every 6 months (U.S. PMOs do not perform this service). Make sure t

meter is located where the ships superstructure will not interfere with th

When observing and recording data, always proceed in a very carefu

ulous manner. An inaccurate observation can mislead the forecaste

in an incorrect forecast. On the other hand, a reliable observation 

key to an obscure or complex meteorological condition. When reco

and wet bulb temperatures, always take your psychrometer to the w

of the ship. This allows contact with air fresh from the sea which ha

over the deck prior to your measurement. 

Accuracy is not only important for forecasting — it is also very impo

climatological purposes and for investigators who may use your obs

later time. A few inaccurate observations can bias results and cause 

conclusions. A researcher has little to go by when deciding about th

of a particular observation, and must depend on the competence o

er aboard ship. 

TRANSMIT REPORTS WITHOUT DELAY (REAL-TIME) 

Always transmit your observations without delay as soon as possible 

you’ve observed the data. Ship reports are used to indicate current

conditions at your vessel (so called real-time conditions). Make you

tion as close to the reporting hour as you can. Any transmission pr

difficulties with radio stations should be reported back to your PM

written in the appropriate space on the back of WS Form B-81 (Sh

Observations), if used. 

Report arrival times tend to be later at night and for Southern Hem

reports. Timely submission of these reports is most important. 

NWSOH No. 1 ix 
out 200 miles from shore). There is also a widespread shortage of data 

Southern Hemisphere and from the arctic ocean. More data is also nee

from the tropics and easterly trade wind belt (5-35 ̊ N), especially durin

Hemisphere hurricane season (May - November). From the North Atlan

North Pacific oceans, more data is needed at 0600 and 1200 UTC (thes

late night and early morning times). If you are operating from a data-sp

area, please report weather regularly. 

NWSOH No. 1 x 
THE VOLUNTARY OBSERVING SHIP PROGRAM 

The Voluntary Observing Ship (VOS) program is organized for the 

obtaining weather and oceanographic observations from moving sh

national program under World Meteorological Organization (WMO

the VOS has over 7300 vessels participating from 60 nations. It is pa

WMO Global Observing System of the World Weather Watch. 

The United States National Weather Service (NWS) VOS program i

in the world with over 600 vessels participating. It closely follows WM

lines for VOS programs. The U.S. program is supported by 12 full-t

Meteorological Officers ((PMOs) in New York, Baltimore, Norfolk, 

Port Everglades, New Orleans, Houston, Los Angeles, Oakland, Sea

Charleston and Chicago), and 4 part-time PMOs (in Honolulu, Anc

Kodiak, and Valdez). The national program office at Stennis Space 

MS manages the program and oversees PMO activities. Observing f

books, supplies, and operating instructions are prepared at the pro

The national office also maintains a VOS Program Computerized D

Management System to record PMO ship visits, vessel mailing addre

equipment inventories, and information about vessel reports. All U

have direct access to this database. 

Both U.S. and foreign flag vessels participate in the U.S. VOS progr

vessel willing to take and transmit observations in marine areas whe

prepares weather forecasts (see appendix D) can join the program. 

The WMO establishes the ships synoptic code, and procedures and 

for the collection and dissemination of observations worldwide. Th

maintains information about countries and vessels participating in 

(available in WMO Publication No. 47, International List Of Selecte

Supplementary, And Auxiliary Ships). 

WMO SHIPS’ SYNOPTIC CODE, FM 13-X 

Coded messages are used for the international exchange of meteor

information. This is because code makes it practical to understand 

data, manually or by computer, for real-time use or later compilatio

tological records. The code also allows data to be transferred intern

high speed, on special data circuits known as the Global Telecomm

System (GTS). 

The WMO code form Code FM 13-X is the ships’ synoptic code, use

er reporting ships. The code form is composed of a set of symbolic 

(actually groups of letters) representing meteorological elements. E

NWSOH No. 1 1-1 
different symbolic letters. See Chapter 2. 

Universal code has been called the twentieth century’s greatest improve

the collection of meteorological data. Prior to code standardization, lac

sistency and difficulty deciphering observations posed enormous proble

the meteorologist. 

Code forms and specifications are determined by international agreeme

WMO committee meetings, usually held in Geneva. Codes are changed 

sionally to meet operational needs — the last major change was in Janu

1982. Some minor changes were made in November, 1994. 

STANDARD WEATHER REPORTING SCHEDULE FOR SHIPS 

The worldwide weather reporting schedule for Voluntary Observing Sh

times daily — at 0000, 0600, 1200, and 1800 UTC. These are the “main 

tic” times, when weather forecasts are prepared and, therefore, when da

needed most. Two of these times, 0000 and 1200 UTC, are most import

when the numerical weather prediction models are initialized with data 

when soundings are released from upper air stations all over the world. 

Reporting weather once every 3 hours when within 300 miles of a name

cal storm or hurricane is also standard practice worldwide. Storm (wind 

48 knots or higher) or special reports for conditions not forecast, much 

than forecast, or for sudden weather changes) should be sent whenever 

tions warrant. 

3-HOURLY WEATHER REPORTING SCHEDULE 

Vessels operating on the Great Lakes, and within 200 miles of the U.S. o

Canadian coastlines (including the coasts of Alaska, Hawaii, and Gulf co

states), are asked to transmit their observations once every three hours 

0000, 0300, 0600, 0900, 1200, 1500, 1800, and 2100 UTC. This special s

is maintained because of a data shortage from near-shore areas. All wea

reports are voluntary — try to follow the recommended reporting sched

best you can. Always give top priority to reports at the main synoptic ho

hour intervals). When shipboard routine permits, follow the 3-hour sch

from coastal waters. 

PORT METEOROLOGICAL OFFICERS (PMOs) 

Port Meteorological Officers (PMOs) spend most of their time visiting s

support of the VOS program. This is to encourage vessels to report wea

instruct observers about procedures and the use of code; to provide obs

supplies, handbooks, and instructions; to calibrate equipment; and, in s

cases, to install, on loan, meteorological instrumentation. A top priority 

PMO is recruiting new vessels into the VOS program. When the PMO c

NWSOH No. 1 1-2 
facsimile products with the PMO — especially any specific problem

The PMO will contact the appropriate party for investigation and c

action. If you have any suggestions to improve the VOS program, m

known to the PMO. 

NWS PORT METEOROLOGICAL OFFIC

More information about the Voluntary Observing Ship Program and 

rological Officers is available on the Worldwide Web at http://www

NWSOH No. 1 1-3 
National Weather Service, NOAA 

Robert A. Luke 110 Main Street, Suite 201 

Voluntary Observing Ship Program Leader South Amboy, NJ 08879-1367 

National Data Buoy Center Tel: 732-316-5409 

Building Bldg. 3203, Room 305B Fax: 732-316-7643 

Stennis Space Center, MS 39529-6000 E-mail: james.luciani@noaa.gov 

Tel: 228-688-1457 

Fax: 228-688-3923 James Saunders, PMO 

E-mail: robert.luke@noaa.gov National Weather Service, NOAA 

Maritime Center I, Suite 287 

ATLANTIC PORTS 2200 Broening Highway 

Baltimore, MD 21224-6623 

Peggy Alander, PMO Tel: 410-633-4709 

National Weather Service, NOAA Fax: 410-633-4713 

2550 Eisenhower Blvd, Suite 312 E-mail: james.saunders@noaa.gov 

P.O. Box 165504 

Port Everglades, FL 33316 GREAT LAKES PORTS 

Tel: 954-463-4271 

Fax: 954-462-8963 Amy Seeley, PMO 

E-mail: peggy.alander@noaa.gov National Weather Service, NOAA 

333 West University Dr. 

John Warrelmann, PMO Romeoville, IL 60446-1804 

National Weather Service, NOAA Tel: 815-834-0600 Ext. 269 

13701 Fang Road Fax: 815-834-0645 

Jacksonville, FL 32218-7933 E-mail: amy.seeley@noaa.gov 

Tel: 904-741-5186 Ext. 117 

Fax: 904-741-0078 GULF OF MEXICO PORTS 

E-mail: john.warrelmann@noaa.gov 

Paula Campbell, PMO 

Tim Kenefick, PMO National Weather Service, NOAA 

NOAA Coastal Services Center Louis Armstrong International A

2234 South Hobson Avenue Box 20026 

Charleston, SC 29405-2413 New Orleans, LA 70141 

Tel: 843-740-1281 Tel: 504-589-4839 

Fax: 843-740-1289 E-mail: paula.campbell@noaa.gov 

E-mail: timothy.kenefick@noaa.gov 

Chris Fakes, PMO 

Peter Gibino, PMO, National Weather Service, NOAA 

National Weather Service, NOAA Houston Area Weather Office 

4034-B Geo. Wash. Mem. Hwy. 1620 Gill Road 

Yorktown, VA 23692-2724 Dickinson, TX 77539-3409 

Tel: 757-877-1692 Tel: 281-534-2640 Ext. 277 

Fax: 757-877-9561 Fax: 281-337-3798 

E-mail: peter.gibino@noaa.gov E-mail: chris.fakes@noaa.gov 

NWSOH No. 1 1-4 
Robert Webster, PMO 

National Weather Service, NOAA 

501 West Ocean Blvd., Room 4480 

Long Beach, CA 90802-4213 

Tel: 562-980-4090 

Fax: 562-980-4089 

E-mail: bob.webster@noaa.gov 

Robert Novak, PMO 

National Weather Service, NOAA 

1301 Clay Street, Suite 1190N 

Oakland, CA 94612-5217 

Tel: 510-637-2960 

Fax: 510-637-2961 

E-mail: bob.novak@noaa.gov 

Patrick Brandow, PMO 

National Weather Service, NOAA 

7600 Sand Point Way, N.E. 

BIN C15700 

Seattle, WA 98115-6349 

Tel: 206-526-6100 

Fax: 206-526-4571 or 6094 

E-mail: pat.brandow@noaa.gov 

Richard Courtney 

National Weather Service, NOAA 

600 Sandy Hook Street, Suite 1 

Kodiak, AK 99615-6814 

Tel: 907-487-2102 

Fax: 907-487-9730 

E-mail: richard.courtney@noaa.gov 

Debra Russell, OIC 

National Weather Service, NOAA 

Box 427 

Valdez, AK 99686-0427 

Tel: 907-835-4505 

Fax: 907-835-4598 

E-mail: debra.russell@noaa.gov 

National Weather Service Al

222 West 7th Avenue #23 

Anchorage, AK 99513-7575 

Tel: 907-271-5135 

Fax: 907-271-3711 

E-mail: larry.hubble@noaa.g

Derek LeeLoy 

Ocean Services Program Co

National Weather Service Pa

HQ 

Grosvenor Center, Mauka To

737 Bishop Street, Suite 220

Honolulu, HI 96813-3201 

Tel: 808-532-6439 

Fax: 808-532-5569 

E-mail: derek.leeloy@noaa.g

UNITED KINGDOM HEA

Marine Superintendent, BD 

Meteorological Office, Met 

Scott Building, Eastern Ro

Bracknell, Berks RG12 2PW 

Tel: +44-1344 855654 

Fax: +44-1344 855921 

Telex: 849801 WEABKA G 

AUSTRALIA HEADQUAR

A.D. (Tony) Baxter, Headq

Bureau of Meteorology 

Regional Office for Victori

150 Lonsdale Street 

Melbourne, Vic 30001 

Tel: +61396694651 

FAX: +61396694168 

NWSOH No. 1 1-5 
psychrometers as a loan for use in taking weather observations. The equ

is expensive and hard to replace. A loan agreement form between the 

and the ship will have to be filled out. If you have such equipment, and 

longer participating in the VOS program, please contact a Port Meteoro

Officer. An equipment pick-up, drop-off, or delivery will be scheduled. 

Equipment supplies are very limited. Please help ensure that equipmen

accounted for and available for new VOS program recruits. 

WHAT TO MAIL IN 

All of your observations (completed on Ships Weather Observations WS 

B-81 or on SEAS archive disks), and, if you have a barograph, your baro

should be mailed to your PMO when you reach port, using the postage 

envelopes. Make sure the month and year and your vessel’s call letters a

clearly shown on each page of the B-81 or disk envelope. After reviewin

reports, the PMO sends them to the National Climatic Data Center (NC

Asheville, NC., where they are archived and used in the compilation of 

logical and historical records. These records are available to the genera

NWSOH No. 1 1-6 
g 

THE SHIPS SYNOPTIC CODE FM13-X 

Code FM-13-X-SHIP, the ships synoptic code, is comprised of 23 gro

bolic letters representing meteorological and oceanographic eleme

identification and ship location data: 

BBXX D.....D YYGGiw 99LaLaLa QcLoLoLoLo iRixhVV 

00fff 1snTTT 2snTdTdTd 4PPPP 5appp 7wwW1W2 8

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1P

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi (or plain 

THREE MAIN SECTIONS OF THE SHIPS’ SYNOPTIC CODE 

The code has three main sections — 0, 1, and 2. Section 0, consistin

5 code groups, contains the identification data (ship report identifi

sign, date, time, location), and units of wind speed used. 

Ships Synoptic Code Section 0 

BBXX D.....D YYGGiw 99LaLaLa QcLoLoLoLo 

Section 0 is a mandatory section. Location, time, and date groups in 

must be included in the report. Any errors or missing data here wil

in the report being discarded. 

Section 1 consists of code groups 6-14 and contains most of the me

data of the report (precipitation and weather data indicators, cloud 

visibility, cloud cover, wind direction and speed, air and dew point t

tures, sea level pressure, tendency, and amount of change, present 

weather, and cloud type). 

Ships Synoptic Code Section 1 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

The first two groups of section 1 are also considered mandatory. Ra

groups does not mean the other groups are less important. All 23 g

weather message are important and should normally be included in 

to completely describe conditions at your vessel. If you send a repor

the first seven groups, it will be accepted, but its usefulness to the m

will be limited. 

NWSOH No. 1 2-1 
and ice data (for any ice accreting on ship or on the sea surface), and t

bulb temperature group. 

Ships Synoptic Code Section 2 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi (or plain lan

For all synoptic code sections, always include the maximum number of 

groups consistent with observed conditions. Any elements not reported 

normally coded with a slash (/). If an entire group of elements is not re

skip the group completely (do not report a group as /////). 

When translating your observations into code, follow all specifications, 

instructions, and code tables very carefully. This will ensure that your co

message contains an accurate description of conditions observed at you

NWSOH No. 1 2-2 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: The symbolic letters BBXX identify a ship report from 

How to Code: As BBXX, always included as the first group of the wea

Remarks: All ship’s weather reports begin with the BBXX indicato

ately identifies the report as a ships weather report, distinguishing 

radio messages. 

NWSOH No. 1 2-3 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Ships call sign consisting of three or more alphanumeric ch

How to Code: Use your vessel’s actual radio call sign.


Remarks: Credit for delivery of your weather report will not be made 

call sign is provided.


NWSOH No. 1 2-4 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Day of the month (UTC) on which the actual observat

Units: Days. 

Method of Measurement: Determined according to Universal Ti

Coordinated (UTC), not by local date or time. 

How to Code: Always with two digits. 01 for the first day of the mon

second day, etc. 

Remarks: At 0000 UTC, record the day just beginning, not the da

just ended. Forgetting to change the day at 0000 UTC is a common 

error. 

NWSOH No. 1 2-5 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: The actual time of observation (UTC) rounded to the nea

whole hour UTC. 

Units: Hours. 

Method of Measurement: Determined according to Universal Time 

Coordinated (UTC), not by local date or time. 

How to Code: Always coded with two digits rounded to the nearest ho

UTC as 06, 1440 UTC as 15, 2350 UTC as 00 (not 24), etc. The range o

is 00 - 23 

Remarks: The actual time of observation is the time at which the baro

read. Round off this time to the nearest hour. Take your barometer rea

after all the other elements have been observed and coded. 

Note: Observations should be submitted no more than 29 minutes pri

29 minutes after the synoptic hour. 

12Z Observation Transmitted at 1129Z: Counted as 11Z observation.


12Z Observation Transmitted between 1130Z and 1229Z: Counted as 12Z Ob

12Z Observation Transmitted at 1230Z: Counted as 13Z Observation.


NWSOH No. 1 2-6 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Indicator for source and units of wind speed. Source is 

measurement was made (either estimated or measured). 

Units: Knots. 

Method of Measurement: Wind speed is either estimated or mea

an anemometer. 

How to Code: U.S. VOS Program vessels report wind speed in kno

when estimating wind speed in knots, or 4 when measuring wind sp

anemometer in knots. 

Some vessels in foreign VOS programs report wind speed in meters 

These vessels should use 0 when estimating wind speed in meters p

1 when measuring wind speed with an anemometer in meters per s

Code flgs. 

0 Wind speed estimated in meters per second 

1 Wind speed obtained from anemometer in meters p

3 Wind speed estimated in knots 

4 Wind speed obtained from anemometer in knots 

Remarks: U.S. VOS program ships are requested to report wind sp

knots. Wind speed estimates are usually based on the state of the se

Beaufort scale. When the sea surface cannot be seen, such as on ve

nights, wind speed estimates can be based on how the wind effects 

objects, or on the feel of the wind (see ff , Code Section 1). 

NWSOH No. 1 2-7 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Ship’s latitude, in degrees and tenths of a degree, measure

terms of degrees north or south of the equator. 

Units: Degrees and tenths of a degree. 

Method of Measurement: Determine latitude using standard shipboa

methods. Tenths is obtained by dividing the number of minutes by 6, an

disregarding the remainder. Ignore seconds. 

How to Code: Always coded with three digits, the first two digits are ac

degrees, the last digit for tenths of a degree. Code 46 ̊ 41’ as 466 (46 ̊ is 

as is, 41’ divided by 6 is 6 5/6, 5/6 is disregarded); 33 ̊ 04’ as 330 (33 ̊ is 

as is, 04’ divided by 6 is 4/6 which is disregarded and coded as 0 in this 

23 ̊ 00’ as 230; 

Conversion of Minutes to Tenths of a Degree 

Minutes Degree 

00’-05’ .0 

06’-11’ .1 

12’-17’ .2 

18’-23’ .3 

24’-29’ .4 

30’-35’ .5 

36’-41’ .6 

42’-47’ .7 

48’-54’ .8 

54’-59’ .9 

Remarks: Latitude can vary from 0 ̊ (coded 000) to 90 ̊ (coded 900). Q

of the globe (Qc) is used to specify whether the latitude is north or sou

NWSOH No. 1 2-8 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Quadrant of the globe. Varies according to your position 

to the equator (0 ̊ latitude) and the Greenwich Meridian (0 ̊ longitu

Units: 

Method of Measurement: Use standard shipboard methods to de

tude and longitude. Then determine quadrant as defined below. 

How to Code: If you are north of the equator (north latitude), Qc 

1 when east of the Greenwich Meridian (east longitude), or as 7 wh

the Greenwich meridian; If you are south of the equator (south lati

coded as 3 when east of the Greenwich meridian, or as 5 when west 

Greenwich meridian. 

The figure for Qc shows whether the latitude is north or south, and the lon

west. Select the appropriate figure from this table. 

West Longitude East Longitude 

North Latitude 7 1 

South Latitude 5 3 

For positions on the equator, and on the Greenwich or 180th meridian, ei

appropriate figures may be used. 

Remarks: Since Qc is needed to fully describe both latitude and lo

very important to code it correctly. Be very careful to code Qc prop

quadrant boundaries, especially when your vessel crosses from one 

another. 

NWSOH No. 1 2-9 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Longitude in degrees and tenths of a degree. Measured in de

or west of the Greenwich Meridian. Values reverse at the international da

Units: Degrees and tenths of a degree. 

Method of Measurement: Use standard shipboard methods. Tenths a

obtained by dividing the number of minutes by 6, and disregarding the 

remainder. Ignore seconds. 

How to Code: Always coded with four digits, with the leading (hundre

figure coded as 0 or 1. The first three digits are actual degrees, the last 

tenths of a degree. Code 142 ̊ 55’ as 1429 (142 ̊ is coded as is, 55’ divide

6 is 9, the remainder is ignored); code 60 ̊ 31’ as 0605 (60 ̊ is coded as 0

31 divided by 6 is 5, the remainder is ignored); code 9 ̊ 40” as 0096 (9° 

as 009, 40” is coded as 6); code 0 ̊ 16’ as 0002 (0° is coded as 000, 16” is 

as 2). 

Conversion of Minutes to Tenths of a Degree 

Minutes Degree 

00’-05’ .0 

06’-11’ .1 

12’-17’ .2 

18’-23’ .3 

24’-29’ .4 

30’-35’ .5 

36’-41’ .6 

42’-47’ .7 

48’-54’ .8 

54’-59’ .9 

Remarks: Longitude can vary from 0 ̊ (coded 0000 on the Greenwich 

Meridian) to 180 ̊ (coded 1800 on the dateline). Quadrant of the globe 

is used to specify whether the longitude is east or west. 

NWSOH No. 1 2-10 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Indicator For Inclusion or Omission of Precipitation D

Units:


Method of Measurement:


How to Code: Always coded as 4 for U.S. VOS program ships. Thi

that the precipitation group is omitted.


Remarks: Precipitation measurements from moving ships are of q

value. U.S. VOS program ships do not report precipitation amount

NWSOH No. 1 2-11 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: ix is the indicator for present and past weather data group 

7wwW1W2. Tells whether the group is included or omitted from the wea

sage. 

Units: 

Method of Measurement: 

How to Code: Code as 1 when group 7wwW1W2 is included in the weat

sage. Code as 3 if group 7wwW1W2 is to be omitted (if present or past we

has not been observed). 

When weather group 7wwW1W2 is: Code iX as: 

included 1 

omitted (no observation, or data not available) 3 

Remarks: ix is usually coded as 1, because present and past weather ar

tant information, and are normally included in the weather message. W

there is no significant weather to report, you should report the kind of 

nificant weather there is, such as cloud development not observable (ww 

or cloud cover 1/2 or less throughout period (W1 = 0). ix is coded as 3 

when present and past weather have not been observed at all (in this ca

7wwW1W2 is omitted (skipped over) from the weather message. Inciden

never transmit a slashed out group as /////; when no data is available 

entire group, it is excluded from the weather message. 

NWSOH No. 1 2-12 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Height above sea surface of the base of the lowest clou

Units: Feet or meters. 

Method of Measurement: Visual estimate. First determine the typ

lowest cloud seen, and then refer to it’s normal height range. As a r

thumb, for a given cloud type, heights are higher in the tropics and 

summer months. 

Approximate Cloud Heights 

Range Polar Regions Temperate Regions Tropical R

High 3,000 to 7,600 meters 

(10,000 to 25,000 feet) 

5,000 to 13,700 meters 

(16,5000 to 45,000 feet) 

6,100 to 18

(20,000 to 

Middle 2,000 to 4,000 meters 

(6,500 to 13,000 feet) 

2,000 to 7,000 meters 

(6,500 to 23,000 feet) 

2,000 to 7

(6,500 to 2

Low Surface to 2,000 meters 

(Surface to 6,500 feet) 

Surface to 2,000 meters 

(Surface to 6,500 feet) 

Surface to 

(Surface to 

How to Code: Code as 0 - 7 for Cumulus, Stratus, Stratocumulus, 

nimbus, or Nimbostratus clouds (these clouds have bases up to 650

Code as 8 or 9 for Altostratus, Altocumulus, and Nimbostratus (the

have bases above 6500 feet). Code as 9 for Cirrus, Cirrostratus, and 

Cirrocumulus (these clouds have bases above 8200 feet). Also code 

no clouds are present. Code as / when the sky is obscured by fog or 

when reporting at night and cloud base height cannot be determin

accordance with the table on the following page. 

NWSOH No. 1 2-13 
0 0 to 50 160 or less 

1 50 to 100 160 to 330 

2 100 to 200 330 to 660 

3 200 to 300 660 to 1000 

4 300 to 600 1000 to 2000 

5 600 to 1000 2000 to 3300 

6 1000 to 1500 3300 to 5000 

7 1500 to 2000 5000 to 6600 

8 2000 to 2500 6600 to 8200 

9 2500 or more, or no clouds 8300 or more, no clouds 

/ Height of base of cloud not known,such as when obscured by fog o

Use higher code figure for heights at dividing line. 

Remarks: Nimbostratus usually has its base under 6500 feet, but may b

er. Discuss your height estimate with the PMO when he comes aboard s

Weather stations on land use reflected pulses of light to measure cloud 

height. You can sometimes check your estimate against a known height

when a cloud base intercepts a mountainous coast. 

For cumulus and cumulonimbus clouds only, the probable height of th

of these clouds can be determined from the difference between the dry 

temperature and the dew point temperature (in Celsius degrees). Multi

difference by 123 to obtain height in meters, or by 405 to obtain height 

feet. Example: Dry bulb = 20°C, dew point = 10°C, the height of cumulu

(20 – 10) ¥ 123 = 1230 meters. This rule is not valid for other cloud typ

does not apply for ragged or fracto cumulus. 

NWSOH No. 1 2-14 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Visibility is the greatest distance an object can be seen a

Units: feet, nautical miles, meters. 

Method of Measurement: Usually a visual estimate. Report preva

visibility — the maximum visibility common to one half or more of 

circle. When visibility is uniform in all directions, prevailing visibility 

are the same. When visibility is not uniform in all directions, determi

visibility by dividing the horizon circle into sectors of visibility. Estima

est visibility common to one half or more of the horizon circle. See th

illustrations. On long ships, when the visibility is low as in dense fog

of known distances onboard. Ships radar can also be used to determ

tances to objects or other ships. The horizon is a useful visibility ma

the horizon appears sharp and clear, your height aboard ship can b

indicate the distance to the horizon (see the distance to the horizo

on the next page). 

How to Code: First determine prevailing visibility. Then code in a

with the table on the following page. 

Remarks: On ships longer than 656 feet (200 meters), code figures 

can be determined using the known distances to shipboard objects. O

longer than 164 feet (50 meters), code figure 90 can be determined 

board objects. For the higher code figures, the observer judges visibil

the appearance of nearby ships, the horizon, or the atmosphere in ge

NWSOH No. 1 2-15 
gsydautgs

90 less than 50 m less than 55 yd. 90 

91 50 but less than 200 m 55 but less than 220 yd. 91 

92 200 but less than 500 m 220 but less than 550 yd. 92 

93 500 but less than 1000 m 550 but less than 1

⁄2 n. mi. 93 1 94 1 but less than 2 km ⁄2 but less than 1 n. mi. 94 

95 2 but less than 4 km 1 but less than 2 n. mi. 95 

96 4 but less than 10 km


97 10 but less than 20 km


98 20 but less than 50 km


99 50 km or more


2 but less than 5 n. mi. 96 

5 but less than 11 n. mi. 97 

11 but less than 27 n. mi. 98 

27 n. mi. or more 99 

The visibility ranges corresponding to various weather types are as follow

90 90 

91 } Heavy snow, heavy drizzle 91 Fog, thick haze 92 { 92 

93 Moderate snow, moderate drizzle 93 

94 94 

95 Heavy rain Mist, haze { 95 

96 } Moderate rain } Light snow, light drizzle 96 

97 97 

98 } Light rain 98

99 99 

Distance to the Horizon at Sea 

Height of eye above the Sea Surface Horizon Distance 

Meters Feet Kilometers Nautical Mile

5 1.52 4.8 2.6 

10 3.05 6.9 3.7 

15 4.57 8.3 4.5 

20 6.10 9.6 5.2 

25 7.62 10.9 5.9 

30 9.14 11.9 6.4 

35 10.67 12.8 6.9 

40 12.19 13.7 7.4 

45 13.72 14.5 7.8 

50 15.24 15.4 8.3 

55 16.76 16.1 8.7 

60 18.29 16.4 9.1 

65 19.81 17.4 9.4 

70 21.34 18.2 9.8 

75 22.86 18.7 10.1 

80 24.38 19.5 10.5 

85 25.91 20.0 10.8 

90 27.43 20.6 11.1 

95 28.96 21.1 11.4 

100 30.48 21.7 11.7 

105 32.00 22.2 12.0 

110 33.53 22.8 12.3 

115 35.05 23.1 12.5 

120 36.58 23.7 12.8 

Distance to the horizon when viewed from various heights. When out of sight o

and other ships, the horizon is an important visibility marker. 

NWSOH No. 1 2-16 
Prevailing visibility is the maximum visibility common to one half (180°) or 

horizon circle. 

NWSOH No. 1 2-17 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: The total fraction of the sky covered by clouds of all types. 

Units: Eighths of the sky. 

Method of Measurement: Visually estimate how many eighths of the 

covered by cloud, regardless of type. It is sometimes easier to estimate h

much of the sky without clouds can be seen, i.e. if two eighths of the sky 

then 6 eighths is covered by cloud. 

How to Code: See table below. 

Code for Total Cloud Cover, N 

Code flgs. Fraction of sky covered 

0 Cloudless 

1 1 eighth or less, but not zero 

2 2 eighths 

3 3 eighths 

4 4 eighths 

5 5 eighths 

6 6 eighths 

7 7 eighths or more but not totally covered 

8 8 eighths, sky completely covered by clouds 

9 Sky obscured by fog, snow, or other meteorological 

phenomena 

/ Cloud cover indescernible for reasons other than 

Code fig. 9, or observation is not made 

Remarks: A mackeral sky (Altocumulus, stratocumulus, or cirrocumul

ing the whole sky) should be coded as N = 7, since breaks are always pre

these cloud forms. When observing clouds through fog, base your estim

N on the amount of clouds that can be seen through the fog. When a c

ly clear sky is observed through fog or haze, report N as 0. 

NWSOH No. 1 2-18 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: True direction, in tens of degrees, from which wind is 

This is a mean direction averaged over a period of ten minutes. 

Units: Degrees, referred to true north (0 ̊T). 

Method of Measurement: Determine true wind direction from e

orientation of sea (wind) waves, or streaks of foam on the sea surfa

apparent wind direction observed aboard ship. 

Method (1) is easiest, because it provides true wind direction indep

the ships movement. Sight along the lines of the sea wave crests. Sin

direction is the same as the direction from which the sea waves are 

is perpendicular (90 ̊) to the advancing waves crests. Also, use lines 

the sea surface (which may appear for Force 7 or greater wind spee

blown foam streaks are parallel to the direction of the true wind. 

Method (2) determines true wind direction from the apparent wind 

experienced on board when the ship is underway). Apparent wind 

two motions — the actual motion of the air (true wind), and the m

ship. Apparent wind direction is best determined by facing directly 

wind on the windward side of the ship. Other good apparent wind 

are funnel smoke, the orientation of shipboard flags or pennants, o

vane. Once apparent wind direction is obtained, you must remove t

of the ship to obtain true wind. See ff for methods of determining t

from apparent wind. 

How to Code: Coded on a scale from 00 to 36 (and 99 for variable

in tens of degrees. Code true north as 36, east as 09, south as 18, we

the table on the following page. 

NWSOH No. 1 2-19 
00

00 Calm 

01 5°-14° 21 205°-214° 

02 15°-24° 22 215°-224° 

03 25°-34° 23 225°-234° 

04 35°-44° 24 235°-244° 

05 45°-54° 25 245°-254° 

06 55°-64° 26 255°-264° 

07 65°-74° 27 265°-274° 

08 75°-84° 28 275°-284° 

09 85°-94° 29 285°-294° 

10 95°-104° 30 295°-304° 

11 105°-114° 31 305°-314° 

12 115°-124° 32 315°-324° 

13 125°-134° 33 325°-334° 

14 135°-144° 34 335°-344° 

15 145°-154° 35 345°-354° 

16 155°-164° 36 355°- 4° 

17 165°-174° 99 Variable, or all 

18 175°-184° directions. 

19 185°-194° 

20 195°-204° 

Remarks: Report the mean wind direction over the ten minute period 

diately preceding observation time. If this time period includes an abru

change in wind direction, only average data obtained after the change. 

apparent or relative wind direction, remember to determine true wind 

reporting. 

NWSOH No. 1 2-20 
1. Set ship’s true course under pointer

(120°).

2. Mark a small dot down from the center

at a distance equal to the ship’s

speed (12 knots). Label this dot T “T.”

T 

W 

T 

W 

NOTE: Apparent wind direction must be related to a true direction. This is 

adding the apparent wind direction relative to the ship’s bow to the ship’s 

(for apparent wind direction use 0° for wind coming directly from the bow, 

clockwise to 359° 1° off the port bow). If the sum is greater than 360, sub

it. 

NWSOH No. 1 2-21 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: True wind speed, measured or estimated as indicated by 

knots or less. 

Units: Knots (U.S. VOS program ships). 

Method of Measurement: Use either (1) the appearance of the sea s

(the sea state) and the Beaufort scale, (2) an anemometer, or (3) the ef

the wind on people or objects aboard ship. Method (1) relies on the ac

the wind to create sea waves, and results in a true wind estimate, so ther

need to factor out the motion of the ship. Refer to the sea state photog

and descriptions as a guide. These assume steady state conditions which 

the wind direction and speed have been relatively steady over many hou

If using method (2), make sure your anemometer is properly calibrated, 

located so the ships superstructure will not interfere with air motion. An 

anemometer provides an apparent wind measurement. Apparent wind is 

wind you experience aboard a moving ship, and is a combination of the 

air motion across the water (true wind you report as ff), and the ship’s m

The only time there is no apparent wind aboard ship is when the vessel i

in the same direction and with the same speed as the true wind. To rem

ship’s motion and determine true wind, you must use either a true wind 

board, or the graphical method, both illustrated on the following pages. 

Method (3) also provides an apparent wind, so like method (2), requires 

of the ship’s motion to determine true wind. Use method (3) when the s

face cannot be seen (such as on very dark nights), and when an anemom

not available. Refer to the table for apparent wind speed indicators. 

How to Code: Code in actual knots. See the table on the next page. F

of 99 knots or greater, code as 99 and report wind speed using group 00

Remarks: When estimating wind speed using the state of the sea and B

continues on 

NWSOH No. 1 2-22 
- 00

(Knots) Speed fort Description sea fully developed 

Average 

00 00 0 Calm Sea like a mirror ....................... - 

01 - 03 02 1 Light Air Ripples with the appearance of 

scales are formed, but without foam crests .......................... 0.1 

04 - 06 05 2 Light breeze Small wavelets, still short but 

more pronounced, crests have a 

glassy appearance and do not 

break ......................................... 0.2 

07 - 10 09 3 Gentle breeze Large wavelets, crests begin to 

break; foam of glassy appearance; perhaps scattered white 

horses ........................................ 0.6 

11 - 16 13 4 Modt. breeze Small waves, becoming longer; 

fairly frequent white horses ....... 1 (

17 - 21 19 5 Fresh breeze Moderate waves, taking a more 

pronounced long form; many 

white horses are formed 

(chance of some spray) ............. 2 

22 - 27 24 6 Strong breeze Large waves begin to form; 

white foam crests are more 

extensive everywhere 

(probably some spray) ............... 3 (

28 - 33 30 7 Near gale Sea heaps up and white foam 

from breaking waves begins to 

be blown in streaks along the 

direction of the wind .................. 4 (

34 - 40 37 8 Gale Moderately high waves of 

greater length; edges of crests 

begin to break into the spindrift; 

the foam is blown in wellmarked streaks along the 

direction of the wind .................. 5.5 (

41 - 47 44 9 Strong gale High waves; dense streaks of 

foam along the direction of the 

wind; crests of waves begin to 

topple, tumble and roll over; 

spray may affect visibility ........... 7 (

48 - 55 52 10 Storm Very high waves with long overhanging crests; the resulting 

foam, in great patches, is blown 

in dense white streaks along 

the direction of the wind; on the 

whole, the surface of the sea 

takes a white appearance; tumbling of the sea becomes heavy 

and shock-like; visibility affected . 9 (

56 - 63 60 11 Violent Storm Exceptionally high waves (small 

and medium-sized ships might 

be for a time lost to view behind 

the waves); the sea is completely 

covered with long white patches 

of foam lying along the direction 

of the wind; everywhere the 

edges of the wave crests are 

blown into froth; visibility affected 11.5 (

64 and over – 12 Hurricane The air is filled with foam and 

spray; sea completely white with 

driving spray; visibility very seriously affected .............................. 14 (

Note: For wind of 99 knots or greater, use 99 for ff, and report wind speed in group 00fff; e.g. fo

100° true at 125 knots, dd = 10, ff = 99, and fff = 125. 

NWSOH No. 1 2-23 
p() 

Less than 1 Calm, smoke rises vertically. 

1 - 3 Smoke drifts from funnel. 

4 - 6 Wind felt on face. Smoke rises at about 80°. 

7 - 10 Wind extends light flag and pennants. Smoke rises at a

11 - 16 Wind raises dust and loose paper on deck. Smoke rise

about 50 ̊. No noticeable sound in the rigging. Slack ha

curve and sway. Heavy flag flaps limply. 

17 - 21 Wind felt strongly on face. Smoke rises at 30 ̊. Slack h

whip while bending continuously to leeward. Taut halya

maintain slightly bent position. Low whistle in the riggi

flag doesn’t fully extend but flaps over entire length. 

22 - 27 Wind stings face in temperature below 2 ̊C. Slight effo

taining balance against the wind. Smoke rises at 15 ̊. B

and taut halyards whip slightly in bent position. Low m

rather than whistle, in the rigging. Heavy flag extends 

more vigorously. 

28 - 33 Necessary to lean slightly into the wind to maintain ba

Smoke rises at 5 ̊ to 10 ̊. Higher pitched moaning and 

heard from rigging. Halyards still whip slightly. Heavy f

extends fully and flaps only at the end. Oilskins and lo

ing inflate and pull against the body. 

34 - 40 Head pushed back by the force of the wind if allowed 

Oilskins and loose clothing inflate and pull strongly. Ha

rigidly bent. Loud whistle from rigging. Heavy flag stra

and whipping. 

continued from 2-21 

scale, remember that heavy rain and floating ice have a dampening effe

the sea surface, so under these conditions, wind speed may be greater t

sea state indicates. There will always be a lag period between the wind s

increasing or decreasing and the sea wave height rising or falling, espec

during a sudden change in wind speed. Wind blowing against a tide or 

current causes a greater than normal sea wave height, while wind blowi

the tide or current causes a smaller than normal sea wave height. When 

of these conditions exist, an adjustment may be needed to your wind sp

estimate. 

NWSOH No. 1 2-24 
0°


270° 90° 

261° 

22 Knots

230° 

15 Knots 

W 

R 

T 

12 Knots 

Direction from which true wind is blowing 

Wind is blowing

from this direction

toward the ship 

120° Ship’s Course T 

Direction fr

the apparen

blowing rela

course T of 

180° 

Ship’s Course	 120° (True) 

Ship’s speed	 12 knots 

Apparent wind direction


relative to the bow 110° R


Apparent wind direction


relative to ship’s course 120° + 110° = 230°


Apparent wind speed 15 knots


1.	 Select a center position. Place a dot and label it “T”. 

2.	 With a vertical line through point T designated as the 0° line, draw a 

ship’s course at 120°. 

3.	 Select a scale and draw an arc across the course line at 12 scale u

representing the ship’s speed as shown in Figure 2.3. Mark the inte

dot and label it “R”. The ship’s course and speed are represented by 

TR. 

4.	 From point R, draw a line for the apparent wind direction (from 230°

the same scale, the apparent wind speed (15 knots); label this point 

tor RW is the relative wind. 

5.	 Complete the triangle by drawing the line TW for the true wind as sh

figure above. The direction is from the same direction as the label re

True Wind, from the “T”. True wind is from 261° (true), 22 knots, whi

N2622. 

NWSOH No. 1 2-25	 
Beaufort Descriptive 

Number Term Knots Specification 

0 Calm 0 Sea like a mirror. 

Beaufort Descriptive 

Number Term Knots Specification 

1 Light Air 1-3 Ripples with the appearance of scales are formed, w

crests. 

NWSOH No. 1 2-26 
Beaufort Descriptive 

Number Term Knots Specification 

2 Light breeze 4-6 Small wavelets, still short, but more pronoun

glassy appearance but do not break. 

Beaufort Descriptive 

Number Term Knots Specification 

3 Gentle 7-10 Large wavelets; crests begin to break; foam o

appearance; perhaps scattered white horses (

NWSOH No. 1 2-27 
Beaufort Descriptive 

Number Term Knots Specification 

4 Moderate 11-16 Small waves, becoming longer; fairly frequent whit

Beaufort Descriptive 

Number Term Knots Specification 

5 Fresh 17-21 Moderate waves, taking a more pronounced long fo

white horses are formed (chance of some spray). 

NWSOH No. 1 2-28 
Beaufort Descriptive 

Number Term Knots Specification 

6 Strong 22-27 Large waves begin to form; the white foam c

extensive everywhere (probably some spray)

Beaufort Descriptive 

Number Term Knots Specification 

7 Near gale 28-33 Sea heaps up and white foam from breaking 

be blown in streaks along the direction of the 

NWSOH No. 1 2-29 
Beaufort Descriptive 

Number Term Knots Specification 

8 Gale 34-40 Moderately high waves of greater length; edges of 

to break into the spindrift; the foam is blown in wel

streaks along the direction of the wind. 

Beaufort Descriptive 

Number Term Knots Specification 

9 Strong gale 41-47 High waves; dense streaks of foam along the direct

wind; crests of waves begin to topple, tumble, and 

spray may affect visibility. 

NWSOH No. 1 2-30 
Beaufort Descriptive 

Number Term Knots Specification 

10 Storm 48-55 Very high waves with long overhanging crest

foam, in great patches, is blown in dense wh

the direction of the wind; on the whole, the se

white appearance; the tumbling of the sea be

shock-like; visibility affected. 

Beaufort Descriptive 

Number Term Knots Specification 

11 Violent 56-63 Exceptionally high waves (small and medium

be lost to view for a time behind the waves); 

pletely covered with long white patches of foa

direction of the wind; everywhere the edges o

are blown into froth; visibility affected. 

NWSOH No. 1 2-31 
WHEN USING THE BEAUFORT SCALE, THE VELOCITY EQUIVALE

AT A STANDARD HEIGHT OF 10 METERS ABOVE THE WATER SUR

Beaufort Descriptive 

Number Term Knots Specification 

12 Hurricane 64 and The air is filled with foam and spray; sea complete

over white with driving spray; visibility very seriously a

In enclosed waters, or when near land, with an off-shore wind, wave heig

be smaller and the waves steeper. 

NWSOH No. 1 2-32 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: High Wind Speed, measured or estimated as indicate

knots or more. 

Units: Knots (For U.S. VOS program ships). 

Method of Measurement: Use the Beaufort scale, or determine a

wind either with an anemometer or by noting effects of the wind on 

objects. Same as for ff, page 2-21. 

How to Code: In actual knots. 99 knots is coded as 099, 110 knots 

110. Whenever fff is used to report a very high speed wind, ff in gro

coded as 99. 

Remarks: For wind of 98 knots or less, ff is used to report wind sp

group 00fff is omitted from the weather message. 

NWSOH No. 1 2-33 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: sn is the arithmetic sign of the air temperature.


Units: Celsius degrees.


Method of Measurement: Thermometer or psychrometer.


How to Code:


Code for Sign of Air Temperature, sn 

Code flgs. 

0 Temperature is positive or zero 

1 Temperature is negative 

Remarks: See remarks under TTT. 

NWSOH No. 1 2-34 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Air temperature, in whole degrees and tenths of a degr

sign being given by Sn. It is a measure of the heat content of the air

Units: Celsius degrees. 

Method of Measurement: Thermometer or psychrometer. When 

thermometer, the eye must be at the same level as the end of the m

umn. Take the reading from the windward side of the ship in a stre

fresh from the sea, which has not been in contact with, or passed ov

The thermometer should be shielded from radiation, precipitation

How to Code: In actual Celsius degrees (to tenths of a degree). 

Examples: 12.1°C: TTT= 121 and Sn=0 

4.2°C: TTT= 042 and Sn=0 

0.8°C: TTT= 008 and Sn=0 

–0.8°C: TTT= 008 and Sn=1 

–6.2°C: TTT= 062 and Sn=1 

Remarks: If a fixed location louvered screen psychrometer is used

be installed on each side of the ship, so the observation can always 

from the windward side. If using a sling psychrometer stored inside

sufficient time for the thermometer to adjust to the outside temper

NWSOH No. 1 2-35 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: sn is the sign of the dew point temperature.


Units: Celsius degrees.


Method of Measurement: Psychrometer.


How to Code:


Code for Sign of Dew Point Temperature, sn 

Code flgs. 

0 Temperature is positive or zero 

1 Temperature is negative 

Remarks: See remarks under TTT. 

NWSOH No. 1 2-36 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Dew Point Temperature, in degrees and tenths of a degr

its sign being given by sn. This is the temperature at which condensat

occur, causing dew or frost to form. It corresponds to a relative humi

Units: Celsius degrees. 

Method of Measurement: Computed from the wet and dry bulb 

tures. Using the psychrometer, determine the dry and wet bulb tem

Then compute the wet-bulb depression (difference between the dry 

bulb temperatures). Locate the dew point temperature using the ta

next page. 

How to Code: In actual degrees Celsius, using a slash (/) for the t

(for U.S. VOS program ships). Report 5°C as 05/, 11°C as 11/, etc. 

Examples: 9°C: TdTdTd=09/ and sn=0 

–9°C: TdTdTd=09/ and sn=1 

–15°C: TdTdTd=15/ and sn=1 

Remarks: The wet bulb thermometer must be read as soon as pos

ventilation or whirling has stopped. Since dew point temperatures a

to the nearest whole degree, the tenths figure is always reported as 

and wet bulb temperatures are reported to the nearest tenth of a d

To operate the sling psychrometer: 

Moisten the wet bulb muslin sleeve thoroughly, on all sides, with distille

the purest water available (ordinary water contains dissolved substances 

on the wicking as it evaporates, causing the wet bulb to read high). Chang

weekly, or more often if it becomes dirty or contaminated by salt spray. 

From the windward side of the ship, whirl the psychrometer at a rate of 

lutions per second for about 1 minute. Read the thermometers immediate

for another 10 seconds, and read again. If the readings are unchanged, re

your official temperatures. If the readings are different at the second readi

the whirling and reading until two successive sets of readings are the sam

NWSOH No. 1 2-37 
snow, or other cold object. This may need to be done up to a half hour before o

tion time, to allow enough time for the ice coating to form. Do not allow the coat

on the wet bulb to become too thick—this will result in an incorrect reading. If ic

ing up, immerse the wet bulb in a small container of warm water to reduce the 

Dew Point Calculation Table 

Subtract wet-bulb temperature from dry-bulb temperature to get “wet-bulb de

Locate nearest depression across top of table and nearest wet-bulb tempera

the side. Read encoded dew point at intersection of wet-bulb temperature 

depression column. The dew point temperature, TdTdTd, should always be les

air temperature TTT. For wet-bulb depressions greater than 11-C, please re

American Practical Navigator: Bowditch. 

-16 

-15 

-14 

-13 

-12 

-11 

-10 

-9 

-8 

-7 

-6 

-5 

-4 

-3 

-2 

-1 

0 

+1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

WetBulb 

Temp. 

(°C) 

-18 -21 -25 -30 -40 

-17 -19 -23 -27 -34 -54 

-16 -18 -21 -25 -30 -42 

-15 -17 -19 -23 -27 -35 

-13 -16 -18 -21 -24 -30 

-12 -14 -16 -19 -22 -26 

-11 -13 -14 -17 -20 -24 

-10 -12 -13 -15 -18 -21 

-9 -10 -12 -14 -16 -19 

-8 -9 -11 -12 -14 -17 

-7 -8 -9 -11 -12 -15 

-6 -7 -8 -9 -11 -13 

-5 -6 -7 -8 -9 -11 

-3 -4 -5 -7 -8 -9 

-2 -3 -4 -5 -6 -7 

-1 -2 -3 -4 -5 -6 

00 -1 -2 -2 -3 -4 

01 00 -1 -1 -2 -3 

02 01 01 00 -1 -2 

03 02 02 01 00 -1 

04 03 03 02 02 01 

05 04 04 03 03 02 

06 06 05 04 04 03 

07 07 06 06 05 04 

08 08 07 07 06 06 

09 09 08 08 07 07 

10 10 09 09 08 08 

11 11 10 10 09 09 

12 12 11 11 11 10 

13 13 12 12 12 11 

14 14 13 13 13 12 

15 15 14 14 14 13 

16 16 15 15 15 15 

17 17 16 16 16 16 

18 18 18 17 17 17 

19 19 19 18 18 18 

20 20 20 19 19 19 

21 21 21 20 20 20 

22 22 22 21 21 21 

23 23 23 22 22 22 

24 24 24 23 23 23 

25 25 25 24 24 24 

26 26 26 26 25 25 

27 27 27 27 26 26 

28 28 28 28 27 27 

29 29 29 29 28 28 

30 30 30 30 29 29 0.0 0.5 1.0 1.5 2.0 2.5

-50 

-40 

-33 

-28 

-24 

-21 

-19 

-17 

-14 

-12 

-11 

-9 

-7 

-5 

-4 

-3 

-1 

00 

01 

03 

04 

05 

06 

07 

09 

10 

11 

12 

13 

14 

15 

16 

17 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 3.0

-48 

-37 

-30 -40 

-26 -32 

-22 -26 

-20 -22 

-17 -19 

-14 -16 

-12 -14 

-10 -12 

-8 -10 

-7 -8 

-5 -6 

-4 -5 

-2 -3 

-1 -2 

01 00 

02 01 

03 03 

04 04 

06 05 

07 06 

08 08 

09 09 

10 10 

12 11 

13 12 

14 14 

15 15 

16 16 

17 17 

18 18 

19 19 

21 20 

22 21 

23 22 

24 24 

25 25 

26 26 

27 27 

28 28 

29 29 3.5 4.0

-43 

-33 -52 

-27 -34 -51 

-23 -27 -34 

-18 -22 -26 -33 

-16 -19 -22 -26 -31 

-14 -16 -18 -21 -25 

-11 -13 -15 -17 -20 

-9 -10 -12 -14 -16 

-7 -9 -10 -12 -13 

-6 -7 -8 -9 -11 

-4 -5 -6 -7 -9 

-2 -3 -4 -5 -7 

-1 -2 -3 -4 -5 

01 00 -1 -2 -3 

02 01 01 00 -1 

03 03 02 01 01 

05 04 03 03 02 

06 05 05 04 04 

07 07 06 06 05 

08 08 07 07 06 

10 09 09 08 08 

11 10 10 10 09 

12 12 11 11 10 

13 13 13 12 12 

14 14 14 13 13 

16 15 15 15 14 

17 16 16 16 15 

18 18 17 17 17 

19 19 18 18 18 

20 20 20 19 19 

21 21 21 20 20 

22 22 22 22 21 

23 23 23 23 23 

24 24 24 24 24 

26 25 25 25 25 

27 26 26 26 26 

28 28 27 27 27 

29 29 29 28 28 

Wet-Bulb Depression °C 4.5 5.0 5.5 6.0 6.5

-36 

-30 

-23 

-19 

-15 

-12 

-10 

-8 

-6 

-4 

-2 

00 

01 

03 

04 

06 

07 

09 

10 

11 

13 

14 

15 

16 

18 

19 

20 

21 

22 

23 

25 

26 

27 

28 7.0

-35 

-28 

-22 

-18 

-14 

-12 

-9 

-7 

-5 

-3 

-1 

01 

02 

04 

05 

07 

08 

10 

11 

12 

14 

15 

16 

17 

19 

20 

21 

22 

23 

24 

26 

27 

28 7.5

-36 

-26 

-20 

-17 

-13 

-11 

-8 

-6 

-4 

-2 

00 

02 

03 

05 

06 

08 

09 

11 

12 

13 

15 

16 

17 

18 

20 

21 

22 

23 

24 

25 

27 

28 8.0

-32 

-24 

-19 

-15 

-12 

-9 

-7 

-5 

-3 

-1 

01 

03 

04 

06 

07 

09 

10 

12 

13 

14 

16 

17 

18 

19 

20 

22 

23 

24 

25 

26 

27 8.5

-29 

-22 

-18 

-14 

-11 

-8 

-6 

-4 

-2 

00 

02 

04 

05 

07 

08 

10 

11 

13 

14 

15 

17 

18 

19 

20 

21 

23 

24 

25 

26 

27 9.0

-39 

-27 

-21 

-16 

-13 

-10 

-7 

-5 

-3 

-1 

01 

03 

05 

06 

08 

09 

11 

12 

14 

15 

16 

18 

19 

20 

21 

22 

24 

25 

26 

27 9.5

NWSOH No. 1 2-38 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: PPPP is the atmospheric pressure at mean sea level, i

hectopascal (millibar), omitting the thousands digit. It represents 

force exerted by the air above a given point. 

Units: Hectopascals ((hp) which are numerically the same as milli

Method of Measurement: Usually measured with a precision ane

eter, although a mercury barometer can also be used. Gently tap th

aneroid barometer just before measurement. To obtain an accurate 

your eye should be level with the barometer face. The mercury in th

the mercury barometer will oscillate up and down. Average the high 

points of the oscillation before recording. 

How to Code: Report the reading in actual hectopascals, omitting 

point. When the sea level pressure is 1000 hp or greater, the leading 

Examples: 992.4 hp: PPPP = 9924 

1000.0 hp: PPPP = 0000 

1002.8 hp: PPPP = 0028 

1032.1 hp: PPPP = 0321 

Remarks: Great precision is required for the pressure measureme

PMO should calibrate your barometer once every three months. T

attach a correction tab with a correction to sea level to be made bef

ing. The barometer should be installed in a position where it is leas

affected by vibration, concussion, or movement of the ship (genera

the center of flotation as possible. The barograph should be installe

pen arm installed athwart ship (parallel to beam), to minimize the 

swinging off the chart. 

NWSOH No. 1 2-39 
m ft. –20 –10 0 10 20 

1.5 5 0.2 0.2 0.2 0.2 0.2 

3.0 10 0.4 0.4 0.4 0.4 0.4 

4.6 15 0.6 0.6 0.6 0.6 0.5 

6.1 20 0.8 0.8 0.8 0.7 0.7 

7.8 25 1.0 1.0 1.0 0.9 0.9 

9.1 30 1.2 1.2 1.2 1.1 1.1 

10.7 35 1.5 1.4 1.4 1.3 1.3 

12.2 40 1.7 1.6 1.5 1.5 1.4 

13.7 45 1.9 1.8 1.7 1.7 1.6 

15.2 50 2.1 2.0 1.9 1.9 1.8 

16.8 55 2.3 2.2 2.1 2.0 2.0 

18.3 60 2.5 2.4 2.3 2.2 2.2 

19.8 65 2.7 2.6 2.5 2.4 2.3 

21.3 70 2.9 2.8 2.7 2.6 2.5 

22.9 75 3.1 2.9 2.8 2.7 2.6 

24.4 80 3.3 3.2 3.1 3.0 2.9 

25.9 85 3.5 3.4 3.3 3.2 3.1 

27.4 90 3.8 3.6 3.5 3.4 3.2 

29.0 95 4.0 3.8 3.7 3.5 3.4 

30.5 100 4.2 4.0 3.9 3.7 3.6 

32.0 105 4.4 4.2 4.1 3.9 3.8 

33.5 110 4.6 4.4 4.2 4.1 4.0 

35.1 115 4.8 4.6 4.4 4.3 4.1 

36.6 120 5.0 4.8 4.6 4.5 4.3 

38.2 125 5.2 5.0 4.8 4.7 4.5 

Station pressure is the actual pressure at the level of the barometer.


This table should only be used if your barometer has not been calibrated to re

level pressure, or if a PMO has not attached a correction sticker. This is norma

case for vessels of British Commonwealth countries only.


Barometers aboard NWS VOS program ships are calibrated to read sea level 

Any correction to be applied will be indicated on the correction sticker and this 

should be ignored.


For Great Lakes vessels: PMOs in Cleveland and Chicago calibrate your baro

read sea level pressure using the elevation of Lake Erie in the correction facto

other Great Lakes, to obtain sea level pressure you must know the difference 

tion between Lake Erie and the lake you are on, and add or subtract a correct

From Lake Huron or Lake Michigan (both 10 feet above Lake Erie), please add 

(see table above) to your pressure reading before reporting. For Lake Superior 

above Lake Erie), add 1.1 hp. For Lake Ontario (325 feet below Lake Erie), subtra

NWSOH No. 1 2-40 
5, Three Hour Pressure Tendency Data Indicator 

SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: (a) is the characteristic of pressure tendency during th

hours preceding the time of observation. It describes how pressure 

e.g. increasing then decreasing, decreasing then increasing, decrea

steady, etc. 

Units: Hectopascals. 

Method of Measurement: The barograph provides the best indic

pressure tendency characteristic. Study the barograph trace in the t

period preceding the time of observation. The shape of the trace d

which code figure to use. 

How to Code: Code according to the table on the next page. 

Remarks: The actual pressure change during the three hours pre

time of observation is recorded by ppp. 

1. Remember that: 

(a) If the pressure is higher than three hours ago, there are four 

a; 0, 1, 2, and 3. 

(b) If the pressure is lower than three hours ago, there are also f

for a; 5, 6, 7, and 8. 

(c) If the pressure is exactly the same as it was three hours ago, 

three choices for a; 0, 4, and 5. 

2. If the trace contains minor irregularities but in general resemble

pictures in the code Table, disregard the minor irregularities and c

eral characteristics of the trace. 

Examples: = 8 =3 

NWSOH No. 1 2-41 
Examples: = 1 = 0 

= 3	 (not 5 as the pressure is now 

higher than 3 hours ago). 

4. When the trace may apparently be represented by two characteristics 

the characteristics of the last part of the trace does not agree with the 3

pressure change, choose the characteristics which is most descriptive of 

whole 3-hour trace and which also agrees with the net 3-hour pressure c

Examples: 

= 5 (not 1 as the pressure is 

lower than 3 hours ago). 

= 0 (not 8 as the pressure is 

higher than 3 hours ago). 

= 0	 (not 6 as the pressure is 

higher than 3 hours ago). 

5. When the trace is not steady but the 3-hour pressure change is zero, 

figure 0 or 5 as appropriate for the last part of the trace (code figure 4 

used when the trace is absolutely steady). 

Examples: = 5 = 0 

NWSOH No. 1 2-42	 
NWSOH No. 1 2-43 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Amount of pressure tendency during the three hours prec

the time of observation, expressed in tenths of a hectopascal (millibar)

the net pressure change during the three hour period. 

Units: Hectopascals. 

Method of Measurement: Either use the barograph trace, or read yo

barometer at the beginning and end of the three hour interval. Determ

difference in pressure and code according to the instructions below. 

How to Code: In actual hectopascals. 

Examples: 0.0 hp, ppp = 000 

0.4 hp, ppp = 004 

4.7 hp, ppp = 047 

10.2 hp, ppp = 102 

Remarks: If the pressure at time of observation is 1015.3 hp, and the p

three hours earlier was 1012.9 hp, the net pressure change (amount of 

tendency) was 2.4 hp. Code ppp as 024. 

NWSOH No. 1 2-44 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: ww is the present weather and refers to atmospheric ph

occurring at the time of observation, or which has occurred during 

preceding the time of observation. 

Units: 

Method of Measurement: Visually or audibly determined. Pheno

report include precipitation, obstructions to visibility, thunder, squa

dust, smoke, and cloud development. 

How to Code: Report the most severe weather condition that you 

reading down the list from 99 (most severe) to 00 (least severe). Co

accordance with the table on the following pages. The higher code

have priority over the lower coded values. Exception: code figure 1

dence over code figures 20 to 49. 

Remarks: There are one hundred different types of present weath

At sea however, phenomena such as duststorms, sandstorms, driftin

snow, and dust whirls are rarely observed. Hence, about eighty-five 

types of present weather are applicable to marine shipboard observ

NWSOH No. 1 2-45 
able (most severe) weather condition that you observe and enter the code numb

59-99 PRECIPITATION AT SHIP AT TIME OF OBSERVATION 

95-99 THUNDERSTORM AT TIME OF OBSERVATION 

99 Heavy thunderstorm with hail* 

98 Thunderstorm with duststorm or sandstorm 

97 Heavy thunderstorm with rain and/or snow, but no hail* 

96 Slight or moderate thunderstorm with hail* 

95 Slight or moderate thunderstorm with rain and/or snow, but no hail* 

* Includes hail, ice pellets or snow pellets 

94-91 THUNDERSTORM DURING THE PAST HOUR BUT NOT AT 

THE TIME OF OBSERVATION 

Note: Use code 29 if there is no precip. at time of observation. 

94 Moderate or heavy snow, or rain and 

snow mixed, or hail* Thunderstorm 

93 Slight snow, or rain and snow mixed, or hail* in past hour 

92 Moderate or heavy rain 

91 Slight rain 

* Includes hail, ice pellets or snow pellets 

85-90 SOLID PRECIPITATION IN SHOWERS 

Slight Moderate 

89 Shower of hail*, no thunder 

87 Shower of snow pellets or ice pellets† 

85 Shower of snow 

†With or without rain, or rain and snow mixed 

*Includes hail, ice pellets or snow pellets 

80-84 RAIN SHOWERS 

84 Shower of rain and snow mixed, moderate or heavy 

83 Shower of rain and snow mixed, slight 

82 Violent rain shower 

81 Moderate or heavy rain shower 

80 Slight rain shower 

NWSOH No. 1 2-46 
79 Ice pellets


78 Isolated star-like snow crystals (with or without fog)


77 Snow grains (with or without fog)


76 Diamond dust (with or without fog)


Intermittent 

74 Heavy snow in flakes 

72 Moderate snow in flakes 

70 Slight snow in flakes 

60-69 RAIN (NOT FALLING AS SHOWERS) 

Slight Mode

68 Rain or drizzle with snow 

66 Freezing rain 

Intermittent 

64 Heavy rain 

62 Moderate rain 

60 Slight rain 

50-59 DRIZZLE 

Slight Mode

58 Drizzle and rain mixed 

56 Freezing drizzle 

Intermittent 

54 Heavy drizzle 

52 Moderate drizzle 

50 Slight drizzle 

00-49 NO PRECIPITATION AT SHIP AT TIME OF OBSERVAT

NWSOH No. 1 2-47 
(Visibility in fog is less than 1⁄2 naut. mi.) 

Sky visible Sky 

48 Fog, depositing rime 

46 Fog, has begun or thickened in past hour 

44 Fog, no change in past hour 

42 Fog, has become thinner in past hour 

41 Fog in patches* 

40 Fog at a distance but not at ship in past hour* 

*Visibility may be greater than 1

⁄2 naut. mi. 

30-39 (Not likely to be used in ship reports) 

Slight or moderate 

38 Blowing snow, high (above eye level) 

36 Drifting snow, low (below eye level 

32 Duststorm or sandstorm, increasing 

31 Duststorm or sandstorm, unchanging 

30 Duststorm or sandstorm, decreasing 

20-29 PHENOMENA IN PAST HOUR BUT NOT AT TIME OF OBS. 

29 Thunderstorm, with or without precipitation 

28 Fog (in past hour but not at time of obs.) 

27 Shower(s) of hail*, or of hail* and rain mixed 

26 Shower(s) of snow, or of rain and snow mixed 

25 Shower(s) of rain 

24 Freezing drizzle or freezing rain 

23 Rain and snow mixed, or ice pellets 

22 Snow 

21 Rain (not freezing) 

20 Drizzle (not freezing) or snow grains 

*Includes hail, ice pellets or snow pellets. 

18-19 SQUALLS, FUNNEL CLOUDS 

19 Funnel cloud(s) seen in past hour or at time of observation 

18 Squalls (no. precip.) in past hour or at time of observation 

17 Thunder at time of observation, no precipitation at ship* 

*Code figure 17 has precedence over code figures 20-49. 

NWSOH No. 1 2-48 
16 Precip. within 3 naut. mi. — reaching surface 

15 Precip. beyond 3 naut. mi. — reaching surface 

14 Precipitation in sight, not reaching surface 

13 Lightning visible, no thunder heard 

10-12 MIST AND SHALLOW FOG 

12 Shallow fog - more or less continuous 

11 Shallow fog in patches 

10 Mist (Visibility 1

⁄2 Nautical mi. or more) 

04-09 HAZE, DUST, SAND OR SMOKE 

09 Duststorm or sandstorm within sight 

08 Dust whirls in past hour (NOT FOR MARINE USE) 

07 Blowing spray at the ship 

06 Widespread dust suspended in the air 

05 Dry haze 

04 Visibility reduced by smoke 

00-03 CHANGE OF SKY DURING PAST HOUR 

Code figs. 

03 Clouds generally forming or developing 

02 State of the sky on the whole unchanged 

01 Clouds dissolving or becoming less developed 

00 Cloud development not observable 

Definitions for Present Weather 

Scheduled Time of Observation is the time at which the observation s

pleted and ready for transmission. These times are the four main synoptic 

0600, 1200, and 1800 UTC, or the intermediate synoptic hours of 0300, 09

2100 UTC. 

At the Time of Observation means at the scheduled time of observation

of code figures 20 through 29, during the 60 minutes prior to the schedu

necessary to make an observation an hour earlier than the scheduled tim

instead of 1200), then “at the time of observation” means 1100. 

NOTE: For the purpose of reporting a thunderstorm, “at the time of observ

the 15 minutes prior to the scheduled time of observation. 

During the Past Hour means during the period starting 60 minutes before 

time of observation. 

NOTE: For purposes of reporting a thunderstorm, code figure 29, the “pas

1 hour and 15 minutes ago to 15 minutes ago. 

NWSOH No. 1 2-49 
Rain. Precipitation of liquid water particles, either in the form of drops larger tha

(0.02 inch) or smaller drops which, in contrast to drizzle, are widely separated

Freezing Rain. Rain which freezes upon impact with the ground or a ship. 

Drizzle. Fairly uniform precipitation composed exclusively of fine drops (diam

than 0.5 mm or 0.02 inch) very close together. Drizzle appears to float while fo

currents, although unlike fog droplets, it falls to the ground. Drizzle drops are to

appreciably disturb still water puddles. 

Freezing Drizzle. Drizzle which freezes upon impact with the ground or a ship

Snow. Precipitation of ice crystals, mostly branched in the form of six-pointed 

temperatures higher than about - 5 ̊C (23 ̊F), the crystals are generally cluster

snowflakes. 

Snow Pellets. Precipitation of white, opaque grains of ice. The grains are round 

times conical. Diameters range from about 2 to 5 mm (0.08 to 0.2 inch). Snow 

brittle and easily crushed; when they fall on hard surfaces, they bounce and often 

Snow Grains. Precipitation of very small, white, opaque grains of ice similar in 

to snow crystals. When the grains hit a hard surface, they do not bounce or sha

usually fall in small quantities, mostly from stratus, and never as showers. 

Ice Pellets. Precipitation of transparent or translucent pellets of ice, which are 

irregular, rarely conical, and which have a diameter of 5 mm (0.2 inch), or less

lets usually rebound when striking hard surfaces and make a sound on impact. 

two main types: 

a. Hard grains of ice consisting of frozen raindrops, or largely melted an

snowflakes (formerly sleet). This type falls as continuous or intermittent pr

b. Pellets of snow encased in a thin layer of ice which has formed from 

ing, either of droplets intercepted by the pellets, or of water resulting 

partial melting of the pellets. This type falls as showers. 

Hail. Precipitation of small balls or other pieces of ice (hail stones) falling sep

frozen together in irregular lumps. Hailstones consist of alternate opaque and 

ers of ice in most cases. Hail is normally associated with thunderstorms and su

peratures above freezing. 

Ice Prisms (Ice Crystals). A fall of unbranched snow crystals in the form of needles

or plates. They are often so tiny that they seem to be suspended in the air. They ma

a cloud or from clear air. The crystals are visible mainly when they glitter in the s

other bright light (diamond dust); they may then produce a luminous pillar or other o

nomena. This hydrometeor (rarely more than the lightest precipitation), which is f

polar regions, occurs only at very low temperatures in stable air masses. 

Character of Precipitation. 

Continuous. Intensity changes gradually, if at all. 

Intermittent. Intensity changes gradually, if at all, but precipitation stops an

least once within the hour preceding the observation.


Shower. Precipitation changes intensity or starts and stops abruptly. Showe

cumuliform clouds.


NWSOH No. 1 2-50 
over the decks; puddles form slowly; sound on roofs ranges from slow pa

tle swishing; steady small streams may flow in scuppers and deck drain

Moderate. Individual drops are not clearly identifiable; spray is observa

deck and other hard surfaces; puddles form rapidly; sound on roofs rang

ing to gentle roar. 

Heavy. Rain seemingly falls in sheets; individual drops are not identifiab

to height of several inches is observed over hard surfaces; visibility is g

sound on roofs resembles roll of drums or distant roar. 

Intensity of Drizzle or Snow with Visibility 

Light. Visibility 1 Km (1/2 n. mile) or more. 

Moderate. Visibility less than 1 Km (1/2 n. mile) but not less than 1/2 K

(1/4 n. mile). 

Heavy. Visibility less than 1/2 Km (1/4 n. mile). 

Estimating the Intensity of Hail and Ice Pellets 

Light. Few stones or pellets falling with little, if any, accumulation. 

Moderate. Slow accumulation. 

Heavy. Rapid accumulation. 

Drifting Snow and Blowing Snow. Snow particles raised from the 

strong, turbulent wind. Observed when ship is in or near ice, not over o

a. Drifting Snow. Snow particles raised by the wind to small heig

ground. Visibility is not reduced below 12 Km (6.5 n. miles) at eye 

obstructions below this level may be veiled or hidden by the pa

nearly horizontal to the ground. 

b. Blowing Snow. Snow particles raised and stirred violently by the 

erate or great heights. Visibility is poor, 12 Km (6.5 n. miles) or les

may become obscured when the particles are raised to great heig

Thunderstorms 

Thunderstorm (Code 99-95). A local storm produced by a cumulonimb

always accompanied by lightning and thunder, usually with strong gusts 

rain, and sometimes with hail. 

Lightning. A flash of light from a sudden electrical discharge which takes 

inside a cloud, from high structures on the ground, or from mountains. 

Intensity of Thunderstorm. The intensity of a thunderstorm is based o

characteristics observed within the previous 15 minutes: 

a. Thunderstorm, wind gusts less than 50 knots, and hail, if any, les

(3/4 inch) in diameter. 

b. Severe thunderstorm, wind gusts of 50 knots or greater, or hail 20 

or greater in diameter. 

NWSOH No. 1 2-51 
b. Overhead lightning or hail is observed, but the local noise level mig

hearing thunder. 

Ending of Thunderstorm. A thunderstorm is considered to have ended 15 min

the last occurrence of thunder. 

Fog and Shallow Fog. A visible aggregate of minute water particles (droplets) 

based at the earth’s surface. The difference between a cloud and fog is that a 

a base above the surface. 

a. Fog (code 40-49) reduces horizontal visibility (to less than 1/2 n. mile) 

cle visibility, and may extend over a sizable area. Fog is reported when 

of the phenomena is greater than approximately 10 meters (33 feet) at 

b. Shallow fog has little vertical extent, normally less than 10 meters (33 

reduces visibility horizontally, but to a lesser extent vertically. The stars 

be seen by night and the sun by day. This is a local phenomena usua

by radiational cooling of the air. It is often patchy, forming first over cool

water areas. 

c. When fog is present and the occurrence does not clearly fit the definitio

low fog, the phenomenon will be reported as fog. If visibility is greater t

mile, it is mist, code 10. 

Ice Fog. A suspension of numerous minute ice crystals in the air, based at t

surface, which reduces horizontal visibility. Unlike fog, ice fog does not produc

glaze on cold exposed objects. Temperatures are usually at or below approxima

(–22 ̊F) when ice fog forms. However, a mixture of liquid and ice fog occasion

at temperatures below freezing. This condition may persist for a few hours a

changes to ice fog and dissipates due to a drying of the air, even though tem

continue to fall. Optical effects similar to those associated with ice prisms are 

in ice fog (diamond dust, etc.). 

Temperature-dew point differences may approach 4 ̊C (8 ̊F) or more. 

Spray and Blowing Spray. 

a. Spray. Water droplets torn by the wind from the crests of waves and ca

short distance into the air. 

b. Blowing Spray. Spray raised in such quantities as to reduce the visibility a

(6 feet on shore, 10 meters (33 feet) at sea) to 12 Km (6.5 n. miles) or le

Dew. A deposit of water drops on objects at or near the surface produced by c

tion of water vapor from the surrounding clear air. 

White Dew. A deposit of white, frozen dew drops. White dew forms as liquid 

freezes. 

Hoar Frost. A deposit of ice having a crystalline appearance, generally ass

form of scales, needles, or fans. It is formed when water vapor is deposited on 

whose temperatures are at or below freezing, as compared to white dew, which 

before freezing occurs. 

Rime. A deposit of ice, produced by fog at temperatures below freezing. It is c

of grains separated by air, sometimes adorned with crystalline branches. 

NWSOH No. 1 2-52 
harder, and more transparent than either rime or hoar frost. 

Tornado. A violent, rotating column of air, forming a pendant, usually from 

bus cloud over land and touching the ground. It nearly always starts as a fu

is accompanied by a loud roaring noise. 

Funnel Cloud. A violent, rotating column of air which does not touch the 

ly a pendant from a cumulonimbus cloud. 

Waterspout. If a funnel cloud forms over the water and touches the wate

called a waterspout. 

Lithometeors. A lithometeor is a meteor consisting of a visible concentra

solid, dry particles. The particles are more or less suspended in the air or 

ground by wind. The more common lithometeors are defined below. 

Haze. A suspension in the air of extremely small, dry particles invisible to 

and sufficiently numerous to give the air an opalescent appearance. This 

resembles a uniform veil that subdues all colors. Dark objects viewed th

tend to have a bluish tinge while bright objects, such as the sun or distant 

have a dirty yellow or reddish hue. 

When haze is present and the sun is well above the horizon, its light may 

liar silvery tinge. Haze particles may be composed of a variety of substan

salt, residue from distant fires or volcanoes, pollen, etc., which generally ar

through the atmosphere. 

Dust. Fine particles suspended in the air by a duststorm or sandstorm 

occurred at some distance from the ship. Dust gives a tan or gray tinge to d

The sun’s disk is pale and colorless, or has a yellow tinge. 

Smoke. A suspension in the air of small particles produced by combus

nomenon may be present either near the earth’s surface or in the free atmo

viewed through smoke, the disk of the sun at sunrise and sunset appears 

disk may have an orange tinge when the sun is above the horizon. Eve

smoke from distant sources generally has a light grayish or bluish appear

tion to haze may occur when smoke particles have traveled great distance

25 to 100 miles or more, and when the larger particles have settled and 

particles have become widely scattered through the atmosphere. 

Blowing Dust. Dust raised by the wind to moderate heights above th

restricting horizontal visibility to less than 12 Km (6.5 n. miles). 

a. Duststorm. Same as blowing dust, except visibility is reduced to 

(1/2 nautical mile) but not less than 1/2 Km (1/4 n. mile). 

b. Severe Duststorm. Same as blowing dust, except visibility is re

than 1/2 Km (1/4 n. mile). 

Blowing Sand. Sand raised by the wind to moderate heights above the 

ing horizontal visibility to less than 12 Km (6.5 n. miles). 

a. Sandstorm. Same as blowing sand, except horizontal visibility is r

than 1 Km (1/2 n. mile) but not less than 1/2 Km (1/4 n. mile). 

b. Severe Sandstorm. Same as blowing sand, except horizon

reduced to less than 1/2 Km (1/4 n. mile). 

NWSOH No. 1 2-53 
harder, and more transparent than either rime or hoar frost. 

Tornado. A violent, rotating column of air, forming a pendant, usually from 

bus cloud over land and touching the ground. It nearly always starts as a fu

is accompanied by a loud roaring noise. 

Funnel Cloud. A violent, rotating column of air which does not touch the 

ly a pendant from a cumulonimbus cloud. 

Waterspout. If a funnel cloud forms over the water and touches the wate

called a waterspout. 

Lithometeors. A lithometeor is a meteor consisting of a visible concentra

solid, dry particles. The particles are more or less suspended in the air or 

ground by wind. The more common lithometeors are defined below. 

Haze. A suspension in the air of extremely small, dry particles invisible to 

and sufficiently numerous to give the air an opalescent appearance. This 

resembles a uniform veil that subdues all colors. Dark objects viewed th

tend to have a bluish tinge while bright objects, such as the sun or distant 

have a dirty yellow or reddish hue. 

When haze is present and the sun is well above the horizon, its light may 

liar silvery tinge. Haze particles may be composed of a variety of substan

salt, residue from distant fires or volcanoes, pollen, etc., which generally ar

through the atmosphere. 

Dust. Fine particles suspended in the air by a duststorm or sandstorm 

occurred at some distance from the ship. Dust gives a tan or gray tinge to d

The sun’s disk is pale and colorless, or has a yellow tinge. 

Smoke. A suspension in the air of small particles produced by combus

nomenon may be present either near the earth’s surface or in the free atmo

viewed through smoke, the disk of the sun at sunrise and sunset appears 

disk may have an orange tinge when the sun is above the horizon. Eve

smoke from distant sources generally has a light grayish or bluish appear

tion to haze may occur when smoke particles have traveled great distance

25 to 100 miles or more, and when the larger particles have settled and 

particles have become widely scattered through the atmosphere. 

Blowing Dust. Dust raised by the wind to moderate heights above th

restricting horizontal visibility to less than 12 Km (6.5 n. miles). 

a. Duststorm. Same as blowing dust, except visibility is reduced to 

(1/2 nautical mile) but not less than 1/2 Km (1/4 n. mile). 

b. Severe Duststorm. Same as blowing dust, except visibility is re

than 1/2 Km (1/4 n. mile). 

Blowing Sand. Sand raised by the wind to moderate heights above the 

ing horizontal visibility to less than 12 Km (6.5 n. miles). 

a. Sandstorm. Same as blowing sand, except horizontal visibility is r

than 1 Km (1/2 n. mile) but not less than 1/2 Km (1/4 n. mile). 

b. Severe Sandstorm. Same as blowing sand, except horizon

reduced to less than 1/2 Km (1/4 n. mile). 

NWSOH No. 1 2-53 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: The types of weather since the previous main synoptic hou

0600, 1200, 1800 UTC), usually different from that being reported by w

for an observation made at 1200 UTC, the past weather period began si

ago at 0600 UTC. For an observation made at an intermediate time, say 

UTC, the past weather period began three hours ago at 1800 UTC. 

Units: 

Method of Measurement: Visually or audibly determined. 

How to Code: If two or more different types of reportable weather hav

occurred, use W1 for the highest code figure, and W2 for the second hig

code figure. If the past weather has been continuous and unchanging s

last main synoptic hour, W1 and W2 are coded the same. W1 is always gr

than or equal to W2. 

Code for Past Weather, W1W2 

Code Figures 

9 Thunderstorm(s) with or without precipitation 

8 Shower(s) 

7 Snow, or rain and snow mixed 

6 Rain 

5 Drizzle 

4 Fog, ice fog, or thick haze (visibility was less than 1

⁄2 nautical 

3 Sandstorm, duststorm, or blowing snow 

2 Cloud cover more than 1

⁄2 throughout period 

1 Cloud cover more than 1

⁄2 for part of period, and 1⁄2 or less for 

another part of period 

0 Cloud cover 1

⁄2 or less throughout period 

NWSOH No. 1 2-54 
W1W2 

(2) During the past six hours thunder was heard (code figure 9), an

about one hour ago there were showers (code figure 8). Code W1W

(3) It has been cloudy since the previous main synoptic hour (code 

rained for about an hour (code figure 6). There was some fog (cod

and there were some showers (code figure 8). CodeW1W2 as 86. 

NWSOH No. 1 2-55 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Nh is the amount of all the CL cloud present or, if no CL cl

present, the amount of all the CM cloud present.


Units: Fraction of the sky in eighths.


Method of Measurement: Visual observation.


How to Code:


Code for Amount of CL or CM Cloud Present, Nh 

Code Figures 

0 No CL or CM clouds present 

1 1 eighth or less, but not zero 

2 2 eighths 

3 3 eighths 

4 4 eighths 

5 5 eighths 

6 6 eighths 

7 7 eighths or more but not totally covered 

8 8 eighths; sky totally covered 

9 Sky obscured by fog, snow, or other meteorological phenome

/ Cloud cover indiscernible for reasons other than code figure 

or observation not made 

Remarks: If the cloud can be seen through the fog, estimate cloud am

well as circumstances permit. If the sun, moon, or stars can be seen thr

fog and there is no evidence of cloud above the fog, use code figure 0 f

NWSOH No. 1 2-56 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Clouds of type Stratocumulus, Stratus, Cumulus and Cu

Stratocumulus (Sc) – Gray or whitish patch, sheet, or layer of clou

almost always has dark parts, composed of te

rounded masses, rolls, etc., which are nonfib

which may or may not be merged; most of t

arranged small elements have an apparent w

more than 5 degrees. 

Stratus (St) – Generally grey cloud layer with a fairly unifo

which may give drizzle, ice prisms, or snow g

the sun is visible through the cloud, its outli

discernible. Stratus generally does not produ

phenomena. 

Cumulus (Cu) – Detached clouds, generally dense and with s

lines, developing vertically in the form of ris

domes, or towers, of which the bulging upp

resembles a cauliflower. The sunlit parts are 

brilliant white; their base is relatively dark an

horizontal. 

Cumulonimbus (Cb) – Heavy, dense cloud, with considerable vertic

the form of a mountain, or huge towers. At 

its upper portion is usually smooth, fibrous, 

and nearly always flattened; this part often s

the shape of an anvil or vast plume. 

Units: 

Method of Measurement: Visual observation. Use the NWS cloud 

cloud brochure, or other suitable cloud atlas which relate cloud ph

to cloud definitions, descriptions, and specifications. It is best to ke

continuous watch on the development of clouds. 

NWSOH No. 1 2-57 
Code Figures 

9 Cb with a clearly fibrous top, often anvil-shaped; with or witho

other Cb, or Cu, Sc, St or ragged Cu or St of bad weather. 

3 Cb the tops of which, at least partially, lack sharp outlines, bu

clearly not fibrous or anvil-shaped; Cu, Sc or St may also be 

present. 

4 Sc formed by the spreading out of Cu; Cu may also be prese

8 Cu and Sc not formed by the spreading out of Cu; the bases 

the Cu and Sc at different levels. 

2 	Cu of moderate or strong vertical extent, generally with protu

ances in the form of domes or towers, with or without other C

Sc, all having their bases at same level. 

Codes 1, 5, 6 and 7 are of equal priority. Choose the cloud type that is predom

1 	Cu with little vertical extent and seemingly flattened, and/or r

Cu other than of bad weather. 

5 Sc not formed by the spreading out of Cu. 

6 St in a more or less continuous layer, and/or in ragged shred

no ragged St of bad weather. 

7 Ragged St and/or ragged Cu, both of bad weather, usually b

As or Ns. 

0 No Sc, St, Cu or Cb clouds present. 

/ Sc, St, Cu and Cb invisible owing to darkness, fog, blowing d

sand, or other similar phenomena. 

Remarks: If more than one type of CL is present, the order of priority 

reporting (from highest to lowest priority) is CL = 9, 3, 4, 8, 2. These ar

followed in priority by CL = 1, 5, 6, 7, all of equal priority (if two or mor

this second category are present, report the type which covers the great

part of the sky). 

NWSOH No. 1 2-58	 
vertical 

CL = 2 

Cumulu

modera

vertical 

CL = 3 

Cumulo

not fibro

not com

no anvi

NWSOH No. 1 2-59 
the spreadin

cumulus. 

CL = 5 

Stratocumul

formed from 

spreading c

CL = 6 

Stratus in a 

layer. 

NWSOH No. 1 2-60 
cumulu

bad we

CL = 8 

Cumulu

stratocu

spreadi

bases a

levels. 

CL = 9 

Cumulo

fibrous 

an anvi

NWSOH No. 1 2-61 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Clouds of type Altocumulus, Altostratus and Nimbostratus. 

Altocumulus (Ac) – White or gray patch, sheet, or layer of cloud, gene

with shading, composed of laminae, rounded mas

rolls, etc, which are sometimes partly fibrous or d

and which may or may not be merged; most of th

larly arranged small elements usually have an app

width between one and five degrees. 

Altostratus (As) – Grayish or bluish sheet or layer of striated, fibrous

form appearance, totally or partly covering the sky

having parts thin enough to reveal the sun at least 

as through ground glass. Does not show halo phen

Nimbostratus (Ns) –	 Heavy cloud layer, often dark, the appearance of 

rendered diffuse by falling rain or snow, which in 

cases reaches the ground. It is thick enough to bl

the sun or moon. 

Units: 

Method of Measurement: Visual observation. 

How to Code: Code in accordance with the table on the following pag

Remarks: If more than one code figure for CM is applicable at the sam

the priority order is CM = 9,8,7,6,5,4,3,2,1,/. 

NWSOH No. 1 2-62	 
9 Ac of a chaotic sky, generally at several levels. 

8 Ac with sproutings like small towers or battlements, or A

the appearance cumulus-shaped tufts. 

7 Either: (a) Ac in two or more layers, opaque in places, not 

(b) Opaque layer of Ac, not increasing. (c) Ac together with 

6 Ac resulting from the spreading out of Cu (or Cb). 

5 Ac, semi-transparent; in bands or Ac in one or more layer

sively invading the sky; these Ac clouds generally thicken a

4 Patches (often almond or fish-shaped) of Ac, mostly semi-

parent; clouds occur at one or more levels and continually 

in appearance. 

3 Ac, mostly semi-transparent; cloud elements change only 

and are all at a single level.. 

2 Either As, most of which is sufficiently dense to hide the s

moon; or Nimbostratus. 

1 Ac, mostly semi-transparent, through which the sun or mo

be weakly visible, as through ground glass. 

0 No Ac, As or Ns clouds present 

/ Ac, As, and Ns invisible owing to darkness, or because o

cast layer of CL cloud. 

NWSOH No. 1 2-63 
transparent, 

moon dimly 

CM = 2 

Altostratus, 

enough to h

or moon, or 

nimbostratu

CM = 3 

Altocumulus

transparent, 

elements ch

slowly, one 

NWSOH No. 1 2-64 
semitra

multilev

elemen

Also alt

lenticula

CM = 

Altocum

more ba

expand

CM = 

Altocum

spreadi

or cumu

NWSOH No. 1 2-65 
more layers

opaque, not 

expanding, o

altocumulus 

altostratus o

nimbostratu

CM = 8 

Altocumulus 

tower like sp

CM = 9 

Altocumulus 

chaotic sky, 

with heavy b

cloud sheets 

different leve

NWSOH No. 1 2-66 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Clouds of type Cirrus, Cirrocumulus, Cirrostratus. 

Cirrus (Ci) –	 Detached clouds in the form of delicate white 

white or mostly white patches or narrow band

clouds have a fibrous appearance (hairlike), o

sheen, or both. 

Cirrocumulus (Cc) –	 Thin white patch, sheet, or layer of cloud with

ing, composed of very small elements in the f

grains, ripples, etc., merged or separate, and 

regularly arranged; most of the elements have 

ent width of less than one degree. 

Cirrostratus (Cs) –	 Transparent, whitish cloud veil of fibrous (ha

smooth appearance, totally or partly covering 

generally producing halo phenomena. 

Units: 

Method of Measurement: Visual observation. 

How to Code: Code in accordance with the table on the following 

Remarks: If more than one code figure for CH is applicable at the 

the priority order is CH = 9,7,8,6,5,4,3,1,2,/. 

NWSOH No. 1 2-67	 
9 Cc alone, or Cc with Ci and/or Cs, but the Cc is predominan

7 Veil of Cs covering the whole sky. 

8 Cs not increasing and not covering the whole sky. 

6 Ci (often in converging bands) and Cs, or Cs alone; in either 

spreading over the sky and generally thickening, the continuo

veil extends more than 45° above the horizon, but does not c

the whole sky. 

5 Same as code 6 above, except that the continuous veil does no

reach 45° above the horizon. 

4 Ci in the form of hooks and/or filaments, progressively invadin

sky; they generally become thicker as a whole. 

3 Dense Ci, often anvil-shaped, being the remains of the upper 

of a Cb. 

1 Ci in the form of filaments, strands or hooks, not progressivel

invading the sky. 

2 Either: (a) Dense Ci in patches or tangled sheaves, not increa

which sometimes seem to be the remains of the upper part of 

(b) Ci with sproutings like small turrets or battlements, or Ci h

the appearance of cumulus-shaped tufts. 

0 No Ci, Cc or Cs clouds present. 

/ Ci, Cc and Cs invisible owing to darkness, or because of a co

uous layer of lower clouds. 

NWSOH No. 1 2-68 
strands

expand

CH = 

Dense 

patches 

not incr

cirrus li

tufts. 

CH = 

Dense 

the anv

from cu

NWSOH No. 1 2-69 
filaments, in

becoming d

CH = 5 

Cirrus band

and/or cirros

increasing, g

denser, veil b

CH = 6 

Cirrus band

and/or cirros

increasing, g

denser, veil 

NWSOH No. 1 2-70 
whole s

CH = 

Cirrostr

increas

coverin

CH = 

Cirrocu

and/or c

cirrostra

NWSOH No. 1 2-71 
Cloud types. 

NWSOH No. 1 2-72 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Ds is the true ship’s course made good during the thre

preceeding the time of observation. 

Units: Compass directions. 

Method of Measurement: If the ships course has been constant d

three hours preceeding the time of observation, then Ds is the actu

the time of observation. However, if the ship has altered course in t

three hours, Ds will probably differ from the course at the time of o

See the diagram on the next page. 

How to Code: 

Code for Ship’s True Course, Ds 

Code Figures True Direction 

0 Ship hove to 

1 NE 

2 E 

3 SE 

4 S 

5 SW 

6 W 

7 NW 

8 N 

9 Unknown 

/ Not reported 

Remarks: From the code table, select the true direction that is clo

course made good. 

NWSOH No. 1 2-73 
0°


270° 90

Course made good 

1500 - 1800 is 

084° 

Position o

ship at 180

(Course 060

Position 

of ship 

at 1500Z 

(Course 130°) 

Ship’s Track 

In this example, the ship has altered course during the past three hours, so cou

good (084°) differs from the actual course at the time of observation (060°). 084

approximately eastward, so Ds is coded as 2. 

NWSOH No. 1 2-74 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Ship’s average speed made good during the three hou

ing the time of observation. 

Units: Knots. 

Method of Measurement: Find the distance in nautical miles, be

ships position at the time of observation and its position three hour

Obtain Vs by dividing this distance by three. vs is the same as the sh

observation time only if the ships course and speed have not chang

the three hour period. 

How to Code: 

Code for Ship’s Average Speed, vs 

Code Figures True Direction 

0 0 knot 

1 1 to 5 knots 

2 6 to 10 knots 

3 11 to 15 knots 

4 16 to 20 knots 

5 21 to 25 knots 

6 26 to 30 knots 

7 31 to 35 knots 

8 36 to 40 knots 

9 Over 40 knots 

/ Not reported 

Remarks: If your vessel has changed course during the three hour 

remember to determine the distance made good of the ship during th

period, and divide this by three. In this case, distance made good is 

the actual distance the ship has travelled. 

NWSOH No. 1 2-75 
0, Sea Surface Data Indicator 

SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: ss is the sign of the sea surface temperature (SST), and also 

cates how the SST was measured. 

Units: Celsius degrees. 

Method of Measurement: Engine room intake thermometer, hull mo

contact sensor thermometer, bucket thermometer. 

How to Code: 

Code for Sign and Type of Sea Surface Temperature, ss 

Code Figures 

0 positive or zero intake measurement 

1 negative intake measurement 

2 positive or zero bucket measurement 

3 negative bucket measurement 

4 positive or zero hull contact sensor 

5 negative hull contact sensor 

6 positive or zero neither intake, bucket or hull 

7 negative neither intake, bucket or hull 

Remarks: Select the appropriate code figure according to the sign of 

surface temperature and method of measurement. 

NWSOH No. 1 2-76 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1P

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Sea surface water temperature, in tenths of a degree C

sign being given by ss. The temperature to be observed is that of th

representative of conditions in the near-surface mixing layer under

ocean skin. 

Units: Celsius degrees. 

Method of Measurement: Engine room intake thermometer, hul

contact sensor thermometer, bucket thermometer. 

How to Code: In actual degrees Celsius as shown below. 

Examples: 8.4°C: TwTwTw = 084 ss = 0 (intake thermometer) 

0.4°C: TwTwTw = 004 ss = 0 (intake thermometer) 

–0.7°C: TwTwTw = 007 ss = 1 (intake thermometer) 

–1.5°C: TwTwTw = 015 ss = 1 (intake thermometer) 

Remarks: It is important to have your sea water thermometer che

calibrated regularly. The engine room intake thermometer should 

every time your vessel goes into the yard for service, and replaced w

essary. 

NWSOH No. 1 2-77 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: PwPw is the period of wind waves in seconds. Wave period i

time between the passage of two successive wave crests (or successive tro

past a fixed point. 

Units: Seconds. 

Method of Measurement: Count seconds, preferably with a watch or 

watch. Note a small object (such as a piece of wood thrown overboard)

of seaweed, patch of foam, or a bird floating on the water. Start countin

the object reaches the crest of the first well formed wave. As the crest p

object will pass into the trough, then to the next crest, etc. Divide the to

elapsed time by the number of crests passing under the object to obtain 

period. 

How to Code: Coded directly in seconds. Thus, if the sea wave period 

seconds, PwPw is coded as 08. 

Remarks: For measuring mean period of a wave system, only consider 

higher waves in the center of each group of well formed waves. Any flat

badly formed waves are omitted from the record. 

Characteristics of a Simple Wave 

NWSOH No. 1 2-78 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1P

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: The vertical distance between trough and crest for win

units of 0.5 meter. 

Units: Half meters. 

Method of Measurement: Visual estimate. It is best for the obser

on the side of the ship from which the waves are coming. On very d

or in dense fog, estimate the wave height based on the last clear sig

whether wind speed or ships motion have changed. 

How to Code: The code is in units of half meters e.g. code figure 

meters = 4 meters = 13 feet: 

Code for Height of Waves, HWHW 

Code Height Code 

figs. in ft. figs. 

(

1

⁄2 m) (

1

⁄2 m) 

Height Code 

in ft. figs. 

(

1

⁄2 m) 

00 Less than 1 10 16 or 17 20 

01 1 or 2 11 18 21 

02 3 or 4 12 19 or 20 22 

03 5 13 21 or 22 23 

04 6 or 7 14 23 24 

05 8 or 9 15 24 or 25 25 

06 10 16 26 or 27 26 

07 11 or 12 17 28 27 

08 13 18 29 or 30 // 

09 14 or 15 19 31 

To obtain the code figures for heights over 45 feet, multiply the height in f

round off the result to the nearest whole number. 

Remarks: As with wave period, consider only the larger well-forme

the center of the wave group. Estimate the average height of these 

and disregard the lesser waves. There is a tendency to underestimat

height if you are fifty feet or more above the sea surface. Your visua

may be more accurate from a lower deck. 

NWSOH No. 1 2-79 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: True direction, in tens of degrees, from which primary swe

are coming. Use swell wave height to distinguish primary from seconda

— the primary or predominant swell system is the one having the highe

waves. Swell are waves that have travelled into your area of observation 

being generated by wind in other areas. 

Units: Degrees. 

Method of Measurement: Visual estimate. Sight along the swell wave 

the primary swell. The direction the swell waves are coming from will be 

the crestline. 

NWSOH No. 1 2-80 
00

Code figure Code flgure 

01 5°-14° 21 205°-214

02 15°-24° 22 215°-224

03 25°-34° 23 225°-234

04 35°-44° 24 235°-244

05 45°-54° 25 245°-254

06 55°-64° 26 255°-264

07 65°-74° 27 265°-274

08 75°-84° 28 275°-284

09 85°-94° 29 285°-294

10 95°-104° 30 295°-304

11 105°-114° 31 305°-314

12 115°-124° 32 315°-324

13 125°-134° 33 325°-334

14 135°-144° 34 335°-344

15 145°-154° 35 345°-354

16 155°-164° 36 355°- 4

17 165°-174° 99 Variable, or a

18 175°-184° direction

19 185°-194° 

20 195°-204° 

Remarks: If there is no swell, or if the swell cannot be distinguishe

swell groups (3dW1dW1dW2dW2, 4PW1PW1HW1HW1, 5PW2PW2HW2HW2

weather message. 

NWSOH No. 1 2-81 
Limits of storm 

Average 

wind 

direction 

Fetch 

Sea 

Swell 

Direction 

of 

waveadvance 

Wave-generat

area 

To distinguish wind waves from swell, remember that wind waves are genera

the wind blowing at the time of observation, or in the recent past, in your loc

Swell waves have travelled into your area of observation, after having been g

by winds in other areas (sometimes thousands of miles away). As wind wave

out from under the wind that produces them and become swell, their charact

changes. The crests become lower and more rounded, and they move in trai

similar period and height. Swell is more symmetrical and uniform than sea, a

have a longer period. 

NWSOH No. 1 2-82 
00

SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1P

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: True direction, in tens of degrees, from which seconda

waves are coming. The secondary swell system has lower waves than 

swell and usually comes from a different direction. 

Units: Degrees. 

Method of Measurement: Visual estimate. Sight along the second

wave crests. The wave direction will be 90° to the crestline. 

How to Code: Use the same code table as for dd, wind direction 

Code for Direction of Secondary Swell, dW2dW2 

Code figure Code flgure 

01 5°-14° 21 205°-214

02 15°-24° 22 215°-224

03 25°-34° 23 225°-234

04 35°-44° 24 235°-244

05 45°-54° 25 245°-254

06 55°-64° 26 255°-264

07 65°-74° 27 265°-274

08 75°-84° 28 275°-284

09 85°-94° 29 285°-294

10 95°-104° 30 295°-304

11 105°-114° 31 305°-314

12 115°-124° 32 315°-324

13 125°-134° 33 325°-334

14 135°-144° 34 335°-344

15 145°-154° 35 345°-354

16 155°-164° 36 355°- 4

17 165°-174° 99 Variable, or a

18 175°-184° direction

19 185°-194° 

20 195°-204° 

Remarks: If only one swell system is observed, use slants (//) for 

ondary swell. 

NWSOH No. 1 2-83 
Primary Swell Waves 

SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Period of primary swell waves, in seconds. Period is the tim

takes two successive swell wave crests to pass a fixed point. 

Units: Seconds. 

Method of Measurement: Same as for wind wave period. Count the s

preferably with a watch or stopwatch. Note a small object, a peice of sea

patch of foam, even a bird floating on the water. Start counting when th

reaches the crest of the first well-formed swell wave. Note the time the o

reaches the next crest, and the crest after that. Record the average peri

several of the larger, well formed swell waves. 

How to Code: Coded directly in seconds. Thus, if the period of the pr

swell waves is 12 seconds, Pw1Pw1 is coded as 12. If the period is 7 secon

Pw1Pw1 is coded as 07. 

Remarks: When the swell wavelength is close to the width of the ship, 

can be estimated by counting the seconds it takes the ship to “ride the s

i.e., go from crest to trough and back to crest. This method is especially 

if the swell is coming from abeam the ship (port to starboard or the rev

NWSOH No. 1 2-84 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Height of primary swell waves, in units of 0.5 meter. Sw

height is the vertical distance between trough and crest. The prima

system has higher waves than the secondary swell. 

Units: Half meters. 

Method of Measurement: Visual estimate. It is best for the observer t

the side of the ship from which the waves are coming. It may help to m

down in the ship (by changing levels or deck) to obtain the best possibl

very dark nights, or in dense fog, estimate the height of the swell waves 

last clear sighting, and whether swell waves have since changed based o

speed or ship’s motion. On bright moonlit nights, swell waves can often 

How to Code: The code is in units of half meters. Thus, code figu

half meters = 5 meters = 16-17 feet. 

Code for Height of Primary Swell Waves, HW1HW1 

Code Height Code 

figs. in ft. figs. 

(

1

⁄2 m) (

1

⁄2 m) 

Height Code 

in ft. figs. 

(

1

⁄2 m) 

00 Less than 1 10 16 or 17 20 

01 1 or 2 11 18 21 

02 3 or 4 12 19 or 20 22 

03 5 13 21 or 22 23 

04 6 or 7 14 23 24 

05 8 or 9 15 24 or 25 25 

06 10 16 26 or 27 26 

07 11 or 12 17 28 27 

08 13 18 29 or 30 // 

09 14 or 15 19 31 

To obtain the code figures for heights over 45 feet, multiply the height in f

round off the result to the nearest whole number. 

Remarks: When determining swell wave characteristics, always sele

er, well formed swell waves of the wave system being observed. Thes

referred to as the “significant” swell waves. 

NWSOH No. 1 2-85 
Swell Waves 

SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Period of secondary swell waves, in seconds. 

Units: Seconds. 

Method of Measurement: Same as for wind wave period. Count the s

preferably with a watch or stopwatch. Note a small object, a peice of sea

patch of foam, even a bird floating on the water. Start counting when th

reaches the crest of the first well-formed swell wave. Note the time the o

reaches the next crest, and the crest after that. Record the average peri

several of the larger, well formed swell waves. 

How to Code: Coded directly in seconds. Thus, if the period of the pr

swell waves is 12 seconds, Pw2Pw2 is coded as 12. If the period is 7 secon

Pw2Pw2 is coded as 07. 

Remarks: When the swell wavelength is close to the width of the ship, 

can be estimated by counting the seconds it takes the ship to “ride the s

i.e., go from crest to trough and back to crest. This method is especially 

if the swell is coming from abeam the ship (port to starboard or the rev

NWSOH No. 1 2-86 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Height of secondary swell waves, in units of 0.5 meter. 

ondary swell system has lower waves than the primary swell. 

Units: Half meters. 

Method of Measurement: Visual estimate. It is best for the observe

the side of the ship from which the swell waves are coming. It may hel

or down in the ship (by changing levels or deck) to obtain the best po

On very dark nights, or in dense fog, estimate the height of the swell w

on the last clear sighting, and whether swell waves have since changed 

the wind speed or ship’s motion. On bright moonlit nights, swell wave

be observed. 

How to Code: The code is in units of half meters. Thus, code figu

half meters = 5 meters = 16-17 feet. 

Code for Height of Secondary Swell Waves, HW2HW2 

Code Height Code 

figs. in ft. figs. 

(

1

⁄2 m) (

1

⁄2 m) 

Height Code 

in ft. figs. 

(

1

⁄2 m) 

00 Less than 1 10 16 or 17 20 

01 1 or 2 11 18 21 

02 3 or 4 12 19 or 20 22 

03 5 13 21 or 22 23 

04 6 or 7 14 23 24 

05 8 or 9 15 24 or 25 25 

06 10 16 26 or 27 26 

07 11 or 12 17 28 27 

08 13 18 29 or 30 // 

09 14 or 15 19 31 

To obtain the code figures for heights over 45 feet, multiply the height in f

round off the result to the nearest whole number. 

Remarks: When determining swell wave characteristics, always sele

well formed swell waves. These are referred to as the “significant” sw

NWSOH No. 1 2-87 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Is is the cause of ice accretion on ship. Ice accretion refers 

deposition of a coating of ice on the ships superstructure or exposed su

from freezing precipitation, ocean spray, supercooled fog, or cloud dro

Units:


Method of Measurement: Visual.


How to Code:


Code for Ice Accretion, Is 

Code Figures 

1 Icing from ocean spray 

2 Icing from fog 

3 Icing from spray and fog 

4 Icing from rain 

5 Icing from spray and rain 

Remarks: An accumulation of freezing rain, drizzle, sea spray, or fog (

ice) can be hazardous, especially to smaller vessels. Ice can cause radio 

failures, due to the icing of aerials. Ice can also cause difficulty in unloa

cargo in port if containers and their lashings are frozen to the deck. By 

ing this information, you alert the forecasters to this condition, enablin

to broadcast reliable warnings when a danger is foreseen. 

NWSOH No. 1 2-88 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Thickness of ice accretion on ships, in centimeters. Re

maximum thickness observed. 

Units: Centimeters.


Method of Measurement: Visual estimate or measured with tape 

ruler. 


How to Code: The code is direct reading in centimeters.


Code for Thickness of Ice Accretion, EsEs 

Code Code Code 

figs. figs. figs. 

(cm) Inches (cm) Inches (cm) 

00 Less than 1⁄4 08 3 or 31⁄4 16 

01 1⁄4 or 1⁄2 09 31⁄2 17 

02 3⁄4 10 33⁄4 or 4 18 

03 1 to 11⁄4 11 41⁄4 or 41⁄2 19 

04 11⁄2 or 13⁄4 12 43⁄4 20 

05 2 13 5 or 51

⁄4 21 

06 21⁄4 or 21⁄2 14 51⁄2 22 

07 23⁄4 15 53⁄4 or 6 23 

Remarks: Report the actual thickness of the ice in centimeters. If 

is 30 cm, code EsEs as 30. 

NWSOH No. 1 2-89 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Rate of ice accretion on ships.


Units:


Method of Measurement: Visual estimate.


How to Code:


Code for Rate of Ice Accretion, Rs 

Code Figures 

0 Ice not building up 

1 Ice building up slowly 

2 Ice building up rapidly 

3 Ice melting or breaking up slowly 

4 Ice melting or breaking up rapidly 

Remarks: 

NWSOH No. 1 2-90 
8, Data Indicator for Wet Bulb Temperature 

SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Arithmetic sign and how the wet bulb temperature was 

Units: Celsius degrees.


Method of Measurement: Psychrometer, either a hand-held sling 

door unit housed in a shelter.


How to Code: 

Code for Sign and Type of Wet Bulb Temperature, Sw 

Code Figures 

0 Positive or zero measured 

1 Negative measured 

2 Iced bulb measured 

3-4 Not used 

5 Positive or zero computed 

6 Negative computed 

7 Iced bulb computed 

Remarks: Psychrometers must be exposed in a stream of air, fresh 

sea, which has not been in contact with, or passed over the ship, an

adequetely shielded from radiation, precipitation, and spray. Take y

surement from the windward side of the ship. If using psychromete

an outdoor shelter, one should be installed on each side of the ship

NWSOH No. 1 2-91 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Wet Bulb temperature, in degrees Celsius and tenths. 

Units: Celsius degrees. 

Method of Measurement: Psychrometer. The thermometers must be 

soon as possible after ventilation or whirling has stopped. Moisten the w

muslin sleeve thoroughly, on all sides, with distilled water, or the purest 

available (ordinary water contains dissolved substances which deposit on 

wicking as it evaporates, causing the wet bulb to read to high). Change 

ing weekly, or more often if it becomes dirty or contaminated by salt sp

If using a sling, from the windward side of the ship, whirl the sling psych

at a rate of about 4 revolutions per second for about 1 minute. Read the 

mometers immediately, then whirl for another 10 seconds, and read aga

readings are unchanged, record these as your official temperatures. If th

ings are different at the second reading, continue the whirling and read

two successive sets of readings are the same. If using psychrometers in ou

shelters, install one on each side of the vessel, and read from the windwa

For temperatures below 0°C, the muslin wicking should be covered with 

coating of ice. After moistening the muslin with ice cold water, you shou

ate the freezing of the water by touching the muslin with a piece of ice, 

other cold object. This may need to be done up to a half hour before o

tion time, to allow enough time for the ice coating to form. Do not allo

coating of ice on the wet bulb to become too thick — this will result in 

rect reading. If ice is building up, immerse the wet bulb in a small cont

warm water to reduce the ice. 

How to Code: The code is direct reading in Celsius degrees. 

Examples: 11.6°C measured: TbTbTb = 116 and sw = 0 

3.2°C measured: TbTbTb = 032 and sw = 0 

–4.8°C computed: TbTbTb = 048 and sw = 6 

NWSOH No. 1 2-92 
The wet bulb thermometer works on the principle that water evapo

the muslin wicking absorbs (removes) heat from the thermometer 

mercury. Whirling therefore lowers the temperature of the wet bulb 

ter. The difference between the readings of the dry and wet bulb th

is called the depression of the wet bulb. 

When the air is very dry, containing little moisture, evaporation will 

and the depression of the wet bulb will be quite large. If the air is v

evaporation from the muslin will be slight, and the depression of th

will be small. At sea, the depression is seldom more than 6°C. 

MUSLIN 

WICKING 

A sling psychrometer. 

NWSOH No. 1 2-93 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Concentration or arrangement of sea ice


Units:


Method of Measurement: Visual determination.


How to Code: Code in accordance with the table on the following pag

Remarks: Choose the coding which describes the condition which is of 

navigational significance.


Lead: Any fracture or pass-way through sea ice which is navigable by surface 

Pack ice: Term used in a wide sense to include any area of sea ice, other tha

no matter what form it takes or how it is disposed.


Sea ice: Any formed ice found at sea which has originated from freezing of se

Pack Ice Coverage 

Code Figures 

Open Water <1/10 (1/8) 

Very Open 1/10 - 3/10 (1/8 < 3/8) 

Open 4/10 - 6/10 (3/8 < 6/8) 

Close 7/10 - 8/10 (6/8 < 7/8) 

Very Close 9/10 - 10/10 (7/8 < 8/8) 

Compact 10/10 (8/8) and no open water visible 

Consolidated 10/10 (8/8) and floes are frozen together 

NWSOH No. 1 2-94 
0 No sea ice in sight 

1 Ship in open lead more than 1


nautical mile wide, or ship in fast


ice with boundary beyond limit of


visibility


2 Sea ice present in concentrations


less than 3

⁄10 (

3

⁄8); open water or
 Sea ice 

-

f

ation

-

aorm in the

observ

the observ

very open pack ice concentra

3	 4

⁄10 to 6⁄10 (

3

⁄8 to less than 6⁄8); open tion is unipack ice 

4 7

⁄10 to 8⁄10 (

6

⁄8 to less than 7⁄8); close 

pack ice area 

5	 9

⁄10 or more, but not 10⁄10 (

7

⁄8 to less 

than 8

⁄8); very close pack ice 

6	 Strips and patches of pack ice 

with open water between 

7	 Strips and patches of close or Sea ice 

very close pack ice with areas of concentra

lesser concentration between tion is not 

8	 Fast ice with open water, very uniform in 

open or open pack ice to seaward


of the ice boundary
 tion area 

9	 Fast ice with close or very close 

pack ice to seaward of the ice 

boundary 

/	 Unable to report, because of 

darkness, lack of visibility, or 

because ship is more than 

1

⁄2 nautical mile away from the 

ice edge. 

NWSOH No. 1 2-95	 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: Stage of Development of Sea ice 

Units: 

Method of Measurement: Visual determination 

How to Code: 

Code for Stage of Development of Sea Ice, Si 

Code Figures 

0 New ice only (frazil ice, grease ice, slush ice, shuga) 

1 Nilas or ice rind, less than 10 cm thick 

2 Young ice (grey ice, grey-white ice), 10-30 cm thick 

3 Predominantly new and/or young ice with some first year ice 

4 Predominantly thin first-year ice with some new and/or young 

5 All thin first-year ice (30-70 cm thick) 

6 Predominantly medium first-year ice (70-120 cm thick) and th

first-year ice (more than 120 cm thick) with some thinner (yo

first-year ice 

7 All medium and thick first-year ice 

8 Predominantly medium and thick first-year ice with some old 

(usually more than 2 meters thick) 

9 Predominantly old ice 

/ Unable to report, because of darkness, lack of visibility, or be

only ice of land origin is visible, or because ship is more tha

1

⁄2 nautical mile away from ice edge 

Remarks: The code figures represent a series of increasing navigation

culties for any concentration of sea ice. 

NWSOH No. 1 2-96 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Ice of land origin


Units:


Method of Measurement: Visual determination.


How to Code:


Code for Ice of Land Origin, bi 

Code Figures 

0 No ice of land origin 

1 1-5 icebergs, no growlers or bergy bits 

2 6-10 icebergs, no growlers or bergy bits 

3 11-20 icebergs, no growlers or bergy bits 

4 Up to and including 10 growlers and bergy bits - no iceb

5 More than 10 growlers and bergy bits - no icebergs 

6 1-5 icebergs with growlers and bergy bits 

7 6-10 icebergs with growlers and bergy bits 

8 11-20 icebergs with growlers and bergy bits 

9 More than 20 icebergs with growlers and bergy bits - a m

to navigation 

/ Unable to report, because of darkness, lack of visibility, o

only sea ice is visible 

Remarks: If only ice of land origin is present, the ice group is cod

e.g. 0/2/0 would mean 6-10 icebergs in sight, but no sea ice. 

NWSOH No. 1 2-97 
SECTION 0  IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiDizi 

Definition: True bearing of principal sea ice edge.


Units:


Method of Measurement: Visual determination


How to Code: 


Code for True Bearing of Principal Ice Edge, Di 

Code Figures 

0 Ship in shore or flaw lead 

1 Principal ice edge towards NE 

2 Principal ice edge towards E 

3 Principal ice edge towards SE 

4 Principal ice edge towards S 

5 Principal ice edge towards SW 

6 Principal ice edge towards W 

7 Principal ice edge towards NW 

8 Principal ice edge towards N 

9 Not determined (ship in ice) 

/ Unable to report, because of darkness, lack of visibility, or be

only ice of land origin is visible 

Remarks: The bearing of the principal ice edge reported should be to 

closest part of that edge. 

NWSOH No. 1 2-98 
SECTION 0 — IDENTIFICATION DATA 

BBXX D . . . . D YYGGiw 99LaLaLa QcLoLoLoLo 

SECTION 1 — METEOROLOGICAL DATA 

iRixhVV Nddff 00fff 1snTTT 2snTdTdTd 

4PPPP 5appp 7wwW1W2 8NhCLCMCH 

SECTION 2 — OCEANOGRAPHIC DATA 

222Dsvs 0ssTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw

5Pw2Pw2Hw2Hw2 6IsEsEsRs 8swTbTbTb ICE ciSibiD

Definition: Present sea ice situation and trend of conditions ove

three hours 

Units:


Method of Measurement: Visual determination. 


How to Code:


Code for Present Ice Situation and Three Hour Trend, z

Code Figures 

0 Ship in open water with floating ice in sight 

1 Ship in easily penetrable ice; conditions improving 

2 Ship in easily penetrable ice; conditions not changing 

3 Ship in easily penetrable ice; conditions worsening 

4 Ship in ice difficult to penetrate; conditions improving 

5 

Ship in 

7 Ice under slight pressure 

8 Ice under moderate or severe pressure 

6	 Ice forming and floes freezing together 

conditions 9	 Ship beset worsening /	 Unable to report, because of darkness, 

lack of visibility 

Ship in ice difficult to penetrate; conditions not changing 

ice difficult to 

penetrate an

Remarks: Code figures 6-9 represents worsening ice conditions di

ship to penetrate. 

NWSOH No. 1 2-99	 
nature of its formation. 

Bergy Bit: A large piece of floating glacier ice, generally showing less than 5 

2

sea level but more than 1 m and normally about 100-300 m in area. 

Beset: Situation of a vessel surrounded by ice and unable to move. 

Brash ice: Accumulations of floating ice made up of fragments not more than 

across, the wreckage of other forms of ice. 

Calving: The breaking away of a mass of ice from an ice wall, ice front, or ice

Close pack ice: Pack ice in which the concentration is 7/10 to 8/10 (6/8 to les

7/8), composed of floes mostly in contact. 

Compacted ice edge: Close, clear-cut ice edge compacted by wind or curren

on the windward side of an area of pack ice. 

Compact pack ice: Pack ice in which the concentration is 10/10 (8/8) and no 

visible. 

Concentration: The ratio expressed in tenths or oktas describing the mean ar

ty of ice in a given area. 

Consolidated pack ice: Pack ice in which the concentration is 10/10 (8/8) and 

floes are frozen together. 

Dark nilas: Nilas which is under 5 cm in thickness and is very dark in color. 

Diffuse ice edge: Poorly defined ice edge limiting an area of dispersed ice; us

the leeward side of an area of pack ice. 

Fast ice: Sea ice which forms and remains fast along the coast, where it is att

the shore, to an ice wall, to an ice front, between shoals or grounded iceberg

fluctuation may be observed during changes of sea level. Fast ice may be form

from sea water or by freezing of pack ice of any age to the shore, and it may ex

few meters or several hundred kilometers from the coast. Fast ice may be more 

year old and may then be prefixed with the appropriate age category (old, seco

or multi-year). If it is thicker than about 2 m above sea level it is called ice shel

Finger rafting: Type of rafting whereby interlocking thrusts are formed, each f

thrusting ‘fingers’ alternately over and under the other. Common in nilas and gr

First-year ice: Sea ice of not more than one winter’s growth, developing from 

ice: thickness 30 cm- 2 m. May be subdivided into thin first-year ice/white ice

um first-year ice, and thick first-year ice. 

Flaw Lead: A passage-way between pack ice and fast ice which is navigable 

face vessels. 

Floating ice: Any form of ice found floating in water. The principal kinds of floa

are lake ice, river ice, and sea ice, which forms by the freezing of water at the 

and glacier ice (ice of land origin) formed on land or in an ice shelf. The con

includes ice that is stranded or grounded. 

NWSOH No. 1 2-100 
Vast: 1.1-5.4 n. mile across 

Big: 500-2000 m across 

Medium: 100-500 m across 

Small: 20-100 m across 

Floeberg: A massive piece of sea ice composed of a hummock, or a grou

mocks, frozen together and separated from any ice surroundings. It may flo

above sea level. 

Fracture: Any break or rupture through very close pack ice, compact pa

consolidated pack ice, fast ice, or a single floe resulting from deformatio

Fractures may contain brash ice and/or be covered with nilas and/or youn

Length may vary from a few meters to many nautical miles. 

Frazil ice: Fine spicules or plates of ice, suspended in water. 

Glacier: A mass of snow and ice continuously moving from higher to lowe

afloat, continuously spreading. The principal forms of glaciers are: inland ic

shelves, ice streams, ice caps, ice piedmonts, cirque glaciers and various 

mountain (valley) glaciers. 

Glacier berg: An irregularly shaped iceberg. 

Glacier ice: Ice in, or originating from, a glacier, whether on land or floati

as icebergs, bergy bits, or growlers. 

Grease ice: A later stage of freezing than frazil ice when the crystals hav

to form a soupy layer on the surface. Grease ice reflects little light, giving th

appearance. 

Grey ice: Young ice 10-15 cm thick. Less elastic than nilas and breaks o

Usually rafts under pressure. 

Grey-white ice: Young ice 15-30 cm thick. Under pressure likely to ridge 

Growler: Smaller piece of ice than a bergy bit or floeberg, often transpa

appearing green or almost black in color, extending less than 1 m above th

and normally occupying an area of about 20m2

. 

Hummock: A hillock of broken ice which has been forced upwards by pre

fresh or weathered. The submerged volume of broken ice under the humm

downwards, is termed a bummock. 

Iceberg: A massive piece of ice greatly varying in shape, more than 5 m a

level, which has broken away from a glacier, and which may be afloat or a

Icebergs may be described as tabular, domed-shaped, sloping, pinnacled, 

glacier bergs. 

Ice boundary: The demarcation at any given time between fast ice and p

between areas of pack ice of different concentrations (cf. ice edge). 

Ice edge: The demarcation at any given time between the open sea and se

kind, whether fast or drifting. It may be termed compacted or diffused (cf. 

Ice front: The vertical cliff forming the seaward face of an ice shelf or oth

glacier varying in height from 2 to 50 m or more above sea level (cf. ice wa

NWSOH No. 1 2-101 
pp

Ice rind: A brittle shiny crust of ice formed on a quiet surface by direct freezing 

grease ice, usually in water or low salinity. Thickness to about 5 cm. Easily bro

wind or swell, commonly breaking in rectangular pieces. 

Ice shelf: A floating ice sheet of considerable thickness showing 2-50 m or mo

sea level, attached to the coast. Usually of great horizontal extent and with a lev

gently undulating surface. Nourished by annual snow accumulation and often a

seaward extension of land glaciers. Limited areas may be ground. The seaward 

termed an ice front. 

Ice stream: Part of an inland ice sheet in which the ice flows more rapidly and 

essarily in the same direction as the surrounding ice. The margins are sometim

marked by a change in direction of the surface slope but may be indistinct. 

Ice under pressure: Ice in which deformation processes are actively occurring 

hence a potential impediment or danger to shipping. 

Ice wall: An ice cliff forming the seaward margin of a glacier which is not afloa

wall is aground, the rock basement being at or below sea level (cf. ice front). 

Lake ice: Ice formed on a lake, regardless of observed location. 

Lead: Any fracture or pass-way through sea ice which is navigable by surface 

Light nilas: Nilas which is more than 5 cm in thickness and rather lighter in co

dark nilas. 

Medium first-year ice: First-year ice 70-120 cm thick. 

Multi-year ice: Old ice up to 3 m or more thick which has survived at least two 

mer’s melt. Hummocks even smoother than in second-year ice, and the ice is 

salt-free. Color, where bare, is usually blue. Melt pattern consists of large inter-c

ing irregular puddles and a well-developed drainage system. 

New ice: A general term for recently formed ice which includes frazil ice, grea

slush, and shuga. These types of ice are composed of ice crystals which are o

weakly frozen together (if at all) and have a definite form only while they are afl

Nilas: A thin elastic crust of ice, easily bending on waves and swell and under 

thrusting in a pattern of interlocking ‘fingers’ (fingers rafting). Has a matt surfac

up to 10 cm in thickness. May be subdivided into dark nilas and light nilas. 

Old ice: Sea ice which has survived at least one summer’s melt. Most topogra

tures are smoother than first-year ice. May be subdivided into second-year an

year ice. 

Open pack ice: Pack ice in which the ice concentration is 4/10 to 6/10 (3/8 to 

6/8), with many leads and polynyas, and the floes are generally not in contact 

another. 

Open water: A large area freely navigable water in which sea ice is present in 

trations less than 1/10 (1/8). There may be ice of land origin present, although 

concentration of all ice shall not exceed 1/10 (1/8). 

NWSOH No. 1 2-102 
yyy ppg yyy 

be covered with new ice, nilas or young ice; submariners refer to these a

Sometimes the polynya is limited on one side by the coast and is called a 

or by fast ice and is called a flaw polynya. If it recurs in the same position e

called a recurring polynya. 

Puddle: An accumulation on ice of melt-water, mainly due to melting snow

more advanced stages also to the melting of ice. Initial stage consists of pa

ed snow. 

Rafting: Pressure process whereby one piece of ice overrides another. M

new and young ice. (cf. finger rafting). 

Ridging: The pressure process in which sea ice is forced into ridges, i.e. a 

broken ice forced up by pressure. 

River ice: Ice formed on a river, regardless of observed location. 

Sea ice: Any formed ice found at sea which has originated from freezing o

Second-year ice: Old ice which has survived only one summer’s melt. Be

er and less dense than first-year ice, it stands higher out of the water. In c

multi-year ice, summer melting produces a regular pattern of numerous s

Bare patches and puddles are usually greenish-blue. 

Shuga: An accumulation of spongy white ice lumps, a few centimeters ac

formed from grease ice or slush and sometimes from anchor-ice rising to 

Slush: Snow which is saturated and mixed with water on land or ice surfa

viscous floating mass in water after a heavy snowfall. 

Strip: Long narrow area of pack ice about 0.5 n. mile or less in width, usu

posed of small fragments detached from the main mass of ice, and run tog

the influence of wind, swell, or current. 

Tabular berg: A flat-topped iceberg. Most tabular bergs form by calving f

shelf and snow horizontal banding. 

Thick first-year ice: First-year ice over 120 cm thick. 

Thin first-year ice/white ice: First-year ice 30-70 cm thick. 

Very close pack ice: Pack ice in which the concentration is 9/10 to less t

to less than 8/8). 

Very open pack ice: Pack ice in which the concentration is 1/10 to 3/10 (1

than 3/8) and water preponderates over ice. 

Young ice: Ice in the transition stage between nilas and first-year ice, 10

thickness. May be subdivided into grey ice and grey-white ice. 

NWSOH No. 1 2-103 
NWSOH No. 1 2-104 
IMPORTANCE OF TIMELY TRANSMISSION 

Your weather observations are used by meteorologists preparing we

casts for coastal, offshore, and high seas areas. They are essential to 

tion of weather charts and analyses for marine areas. It is very impo

observations be transmitted quickly. It is best to transmit reports wit

moments after the observation has been taken — on or within a ver

after the reporting hour. This generally ensures that the report will 

time for use by the marine forecaster. If ship operations prevent tra

or near the reporting hour, send the report as soon as you can, but 

than 3 hours after the time of observation. 

STATIONS ACCEPTING VOS WEATHER OBSERVATIONS 

Weather observations sent by ships participating in the VOS progra

no cost to the ship except as noted. 

The stations listed accept weather observations which enter an auto

tem at National Weather Service headquarters. This system is not in

other types of messages. To communicate with NWS personnel, see 

bers and e-mail addresses at the beginning of this manual. 

NWSOH No. 1 3-1 
Follow the instructions with your INMARSAT terminal for sending a tel

sage. Use the Special Access Code 41 (except when using the AMVER/S

software in compressed binary format with Inmarsat “C” units), and do 

request a confirmation when sending. No cost is involved with this trans

Below is a typical procedure for using an INMARSAT “A” and “B” termin

1. Select appropriate Land Earth Station Identity (LES-ID).


See table below.


2. Select routine priority. 

3. Select duplex telex channel. 

4. Initiate the call. Wait for the GA+ signal. 

5. Select the dial code for meteorological reports, 41+. 

6. Upon receipt of our answerback, NWS OBS MHTS, transmit the w

message starting with BBXX and the ship’s call sign. The message 

ended with 5 periods. Do not send any preamble. 

GA+


41+


NWS OBS MHTS


BBXX WLXX 29003 99131 70808 41998 60909 10250 2021/ 401

71611 85264 22234 00261 20201 31100 40803..... 

The 5 periods indicate the end of the message, and must be includ

each report. Do not request a confirmation. 

INMARSAT “C” 

All major Inmarsat “C” terminals have the ability to transmit the encode

er observation (BBXX) with the Special Access Code 41. No cost is invo

with this transmission. Do not request a confirmation when sending. Th

detailed instructions necessary to setup and address the Code 41 messa

transmission instruction according to the different manufactures are lis

our Website at WWW.VOS.NOAA.GOV under VOS Ship Resource Page

Land-Earth Station Identity (LES-ID) of U.S. Inmarsat Stations Acc

Ships Weather (BBXX) and Oceanographic (JJYY) Reports 

Operator Service Station ID 

AOR-W AOR-E IOR 

TELENOR A 01 01 01 

TELENOR B 01 01 01 

TELENOR C 001 101 304 

TELENOR C (AMVER/SEAS) 001 101 304 

STRATOS/IDB A (octal ID) 13-1 13-1 13-1 

STRATOS/IDB A (decimal ID) 11-1 11-1 11-1 

STRATOS/IDB B 013 013 013 

NWSOH No. 1 3-2 
rant of the globe, (4) requesting a confirmation (which increases co

Using The AMVER/SEAS Software 

The National Oceanic and Atmospheric Administration (NOAA) an

Coast Guard (USCG) have created software to assist Volunteer Obs

(VOS) in submitting weather reports to worldwide weather network

participate in the Automated Mutual (assistance) Vessel Rescue (AM

tem. The VOS program allows commercial ships around the world 

marine weather observations to the National Weather Service. The 

tem allows ships to report their intended track so in the event of an 

all available resources can be focused on aiding ship(s) in distress. 

The U.S. Coast Guard and NOAA pay all transmission costs, provid

are sent to the Inmarsat C address specified in this user’s guide. 

Weather observations should be reported at 0000, 0600, 1200, and 

Ships are also encouraged to submit reports at 0300, 0900, 1500 an

Each weather observation is also processed as a position report then 

Coast Guard AMVER Center. 

A typical voyage when using AMVER/SEAS~MET program would r

submission of an AMVER Sail Plan before departure, submission of 

Observations four times per day and the submission of an Arrival R

U. S. Coast Guard updates their database with the position informa

these reports, which allows them to identify vessels in the vicinity of 

distress. 

Ships that follow the same routes repeatedly have an additional ben

Sail Plans can be stored in the computer system, recalled later to ch

date and time of departure, rather than creating a new plan each ti

Note: To obtain the AMVER/SEAS~Met software program contact a 

or AMVER representative listed at the beginning of this handbook. 

Website at WWW.VOS.NOAA.GOV under Amver/Seas software for 

information. 

Common errors when using the AMVER/SEAS~Met software 

•	 Sending the compressed binary message via the Special Acces

•	 Sending a plain text message via the Amver/Seas address. 

•	 Only TELENOR can accept the Amver/Seas messages in bina

•	 Do not attempt to view the file with the Text Editor. (This wil

unwanted characters to the message and corrupt the file) 

•	 Do not send form the Text Editor. 

•	 Send with the CONFIRMATION request turned OFF. 

NWSOH No. 1 3-3	 
Please note that the vessel will be responsible for the cost of the call. 

GLOBE WIRELESS 650-726-6588


WLO 334-666-5110


Reporting Through United States Coast Guard Stations 

U.S. Coast Guard stations accept SITOR (preferred) or voice radiotelep

weather reports. Begin with the BBXX indicator, followed by the ships c

and the weather message. 

U.S. Coast Guard High Seas Communication Stations 

Ship Ship 

SEL ITU Xmit Rec 

Location (CALL) Mode CAL MMSI # CH# Freq Freq 

Boston (NMF) Voice 003669991 424 4134 4426 

Boston (NMF) Voice 003669991 601 6200 6501 

Boston (NMF) Voice 003669991 816 8240 8764 

Boston (NMF) Voice 003669991 1205 12242 13089 

Chesapeake (NMN) SITOR 1097 604 6264.5 6316 

Chesapeake (NMN) SITOR 1097 824 8388 8428 

Chesapeake (NMN) SITOR 1097 1227 12490 12592.5 

Chesapeake (NMN) SITOR 1097 1627 16696.5 16819.5 

Chesapeake (NMN) SITOR 1097 2227 22297.5 22389.5 

Chesapeake (NMN) Voice 003669995 424 4134 4426 

Chesapeake (NMN) Voice 003669995 601 6200 6501 

Chesapeake (NMN) Voice 003669995 816 8240 8764 

Chesapeake (NMN) Voice 003669995 1205 12242 13089 

Miami (NMA) Voice 003669997 601 6200 6501 

Miami (NMA) Voice 003669997 1205 12242 13089 

Miami (NMA) Voice 003669997 1625 16432 17314 

New Orleans (NMG) Voice 003669998 424 4134 4426 

New Orleans (NMG) Voice 003669998 601 6200 6501 

New Orleans (NMG) Voice 003669998 816 8240 8764 

New Orleans (NMG) Voice 003669998 1205 12242 13089 

Kodiak (NOJ) SITOR 1106 407 4175.5 4213.5 

Kodiak (NOJ) SITOR 1106 607 6266 6317.5 

Kodiak (NOJ) SITOR 1106 807 8379.5 8419.5 

Kodiak (NOJ) Voice 0036698991 *** 4125 4125 

Kodiak (NOJ) Voice 0036698991 601 6200 6501 

Pt. Reyes (NMC) SITOR 1096 620 6272.5 6323.5 

Pt. Reyes (NMC) SITOR 1096 820 8386 8426 

Pt. Reyes (NMC) SITOR 1096 1620 16693 16816.5 

Pt. Reyes (NMC) Voice 003669990 424 4134 4426 

Pt. Reyes (NMC) Voice 003669990 601 6200 6501 

Pt. Reyes (NMC) Voice 003669990 816 8240 8764 

Pt. Reyes (NMC) Voice 003669990 1205 12242 13089 

Honolulu (NMO) SITOR 1099 827 8389.5 8429.5 

NWSOH No. 1 3-4 
Honolulu (NMO) Voice 0036699931 601 6200 65

Honolulu (NMO) Voice 0036699931 816 8240 87

Honolulu (NMO) Voice 0036699931 1205 12242 13

Guam (NRV) SITOR 1100 812 8382 84

Guam (NRV) SITOR 1100 1212 12482.5 12

Guam (NRV) SITOR 1100 1612 16689 16

Guam (NRV) SITOR 1100 2212 22290 22

Guam (NRV) Voice 0036699941 601 6200 65

Guam (NRV) Voice 0036699941 1205 12242 13

Stations also maintain an MF/HF DSC watch on the following frequ

2187.5 kHz, 4207.5 kHz, 6312 khz, 8414.5 Khz, 12577 kHz and 1680

1 MF/HF DSC has not yet been implemented at thes

2 2300-1100 UTC Nights, 1100-2300 UTC Days 

3 2230-1030 UTC Nights, 1030-2230 UTC Days 

4 0600-1800 UTC Nights, 1800-0600 UTC Days 

5 0900-2100 UTC Nights, 2100-0900 UTC Days 

Voice frequencies are carrier (dial) frequencies. SITOR and DSC fr

are assigned frequencies. 

Note that some stations share common frequencies. 

An automated watch is kept on SITOR. Type “HELP+” for the of in

“OBS+” to send the weather report. 

For the latest information on Coast Guard frequencies, visit their w

www.navcen.uscg.gov/marcomms 

U.S. Coast Guard Group Communication Stations 

U.S. Coast Guard Group communication stations monitor VHF mar

16 and 22A and/or MF radiotelephone frequency 2182 kHz (USB)

stations do not have MF installations. 

The following stations have MF DSC installations and also monitor 

DSC. Additional stations are planned. Note that although a station 

as having DSC installed, that installation may not have yet been dec

tional. The U.S. Coast Guard is not expected to have the MF DSC n

installed and declared operational until 2004 or thereafter. 

The U.S. Coast Guard is not expected to have an VHF DSC network 

and declared operational until 2005 or thereafter. 

NWSOH No. 1 3-5 
CAMSLANT Chesapeake VA MF/HF  003

COMMSTA Boston MA MF/HF Remoted to CAMSLANT 003

COMMSTA Miami FL MF/HF Remoted to CAMSLANT 003

COMMSTA New Orleans LA MF/HF Remoted to CAMSLANT 003

CAMSPAC Pt Reyes CA MF/HF — 003

COMMSTA Honolulu HI MF/HF Remoted to CAMSPAC 003

COMMSTA Kodiak AK MF/HF — 003

Group Atlantic City NJ MF 003

Group Cape Hatteras NC MF 003

Group Southwest Harbor MF 003

Group Eastern Shore VA MF 003

Group Mayport FL MF 003

Group Long Island Snd MF 003

Act New York NY MF 003

Group Ft Macon GA MF 003

Group Astoria OR MF 003

Reporting Through Specified U.S. Commercial Radio Stations 

If a U.S. Coast Guard station cannot be communicated with, and your s

is not INMARSAT equipped, U.S. commercial radio stations can be use

your weather observations to the NWS. When using SITOR, use the com

“OBS +”, followed by the BBXX indicator and the weather message. Exa

OBS +	 BBXX WLXX 29003 99131 70808 41998 60909 10250 

40110 52003 71611 85264 22234 00261 20201 31100 

Commercial Stations affiliated with ShipCom LLC (Formally Mobile Ma

Radio, Inc) WLO and KLB accept weather messages via SITOR, with 

Radiotelephone 24 Hours/7 Days Week. 

MARITEL Marine Communication System accepts weather messages via 

marine radiotelephone from near shore (out 50-60 miles), and from th

Great Lakes. 

Globe Wireless 

This company no longer provides a SITOR service. However, the Globe 

HF worldwide Email network does accept OBS weather observations fre

charge to the ship. For information about how to take advantage of this 

contact Globe Wireless at CustomerSupport@Globewireless.com 

Stations located in Argentina, Australia, Bahrain, Barbados, Bolivia, Cal

Canada, China, Guam, Hawaii, Korea, Louisiana, Malaysia, Malta, New 

Norway, South Africa, Sweden and Switzerland will accept OBS weather 

tions from any of the more than 4000 vessels registered Globe Wireless. 

NWSOH No. 1 3-6	 
described in this Handbook. 

ShipCom LLC (Formally Mobile Marine Radio Inc) 

Callsign: Mode SelCal MMSI ITU Ch ShipTx 

WLO SITOR 1090 003660003 406 4175 

WLO SITOR 1090 003660003 606 6265.5 

WLO SITOR 1090 003660003 806 8379 

WLO SITOR 1090 003660003 810 8381 

WLO SITOR 1090 003660003 815 8383.5 

WLO SITOR 1090 003660003 1205 12479 

WLO SITOR 1090 003660003 1211 12482 

WLO SITOR 1090 003660003 1605 16685.5 

WLO SITOR 1090 003660003 1615 16690.5 

WLO SITOR 1090 003660003 1810 18875 

WLO SITOR 1090 003660003 2215 22291.5 

WLO VOICE 003660003 MF/calling 2182 

WLO VOICE 003660003 405 4077 

WLO VOICE 003660003 414 4104 

WLO VOICE 003660003 607 6218 

WLO VOICE 003660003 824 8264 

WLO VOICE 003660003 830 8282 

WLO VOICE 003660003 1212 12263 

WLO VOICE 003660003 1226 12305 

WLO VOICE 003660003 1607 16378 

WLO VOICE 003660003 1641 16480 

WLO VOICE 003660003 1807 18798 

WLO VOICE 003660003 2237 22108 

WLO VOICE 25 VHF 

WLO VOICE 84 VHF 

WLO VOICE 87 VHF 

WLO VOICE 28 VHF 

WLO DSC 003660003 70 VHF 

WLO DSC 003660003 HF 4207.5 

WLO DSC 003660003 HF 8414.5 

WLO DSC 003660003 HF 12577 

WLO DSC 003660003 HF 16804.5 

KLB VOICE 417 4113 

KLB VOICE 805 8207 

KLB VOICE 1209 12254 

KLB VOICE 1624 16429 

KLB SITOR 1113 003660003 408 4176 

KLB SITOR 1113 003660003 608 6266.5 

KLB SITOR 1113 003660003 818 8385 

KLB SITOR 1113 003660003 1223 12488 

KLB SITOR 1113 003660003 1604 16685 

HOURS OF OPERATION ARE 24/7 CONTINUOUS FOR ALL MODES 

NWSOH No. 1 3-7 
Operators are on duty 24 hour per day 7 day per week for assistance. 

Vessels participating in the OBS program may download weather produ

SITOR ARQ on demand at no charge. 

—The command is WX+ for a list of products available. 

—The command OPR+ alerts our operator. 

For the latest information on ShipCom LLC, visit their Website page at: 

www.shipcom.com 

Ship Telex Automatic System Computer Commands and 

Guidelines for Contacting Mobile Marine Radio stations. 

Ship Station Response Land Station Response 

1) INITIATE ARQ CALL 

4) SHIP’S ANSWERBACK IDENTITY 

6) Send Command 

OBS+ (Weather Observations) 

OPR+ (Operator Assistance) 

HELP+ (Operator Procedure) 

9) SEND MESSAGE 

10) KKKK (End of Message Indicator, 

WAIT for System Response 

DO NOT DISCONNECT) 

12) SHIP’S ANSWERBACK 

15) GO TO STEP 6, or 

16) BRK+? Clear Radio Circuit) 

2) RTTY CHANNEL 

3) “WHO ARE YOU” 

(Requests Ship’ Answerback) 

5) GA+? 

7) MOM 

8) MSG+? 

11) RTTY CHANNEL 

13) SYSTEM REFERENCE, 

INFORMATION, TIME,DUR

14) GA+? 

Stations listed as being 24hr may not be operational during periods of p

pogation. 

For the latest information on Mobile Marine Radio frequencies, visit th

page at: http://www.wloradio.com 

NWSOH No. 1 3-8 
program may do so by sending unclassified weather observations in 

code (BBXX format) to the following Plain Language ADdress (PL

SHIP OBS NWS SILVER SPRING MD 

As weather observations received by NWS are public data, vessels sh

with their local command before participating in the VOS Program

WHEN TO USE U.S. RELAY STATIONS 

Transmit your weather observations using a U.S. relay station (U.S. 

INMARSAT, or specified commercial) when you are operating with

forecast and warning areas, shown below: 

Pacific Ocean: 160° east eastward to the coast, and north of 25° so

Atlantic Ocean: 35° west westward to the coast, including the Gulf O

and Carribean Sea, and north of 3° north 

Guam Area: Between 5° north and 25° north, and from 135° eas

When outside these areas, send your observations to the nearest for

that appears on this Internet Website. 

— www.wmo.ch/web/aom/marprog/Operational-Information/i

code41-stations.htm 

— www.bom.gov.au/jcomm/vos 

– Go to Links and Resources/Operational Information/LE

Ship Reports. 

Note:	 When using stations listed on this Website, according to the 

your vessel will not have to pay transmission costs. The hos

ments pick up costs. 

NWSOH No. 1 3-9	 
NWSOH No. 1 3-10 
A man who is not afraid of the sea will soon be drowned, for he’ll be g

out on a day he shouldn’t. But we do be afraid of the sea, and we do 

drowned now and again. 

From The Arran Islands by J. M

Nothing affects the mariner as completely as does the weather. Ant

changes to both weather and sea conditions can be of critical impo

forecast what lies ahead you should capitalize on every available lea

weather. This includes (1) understanding your own observations, an

interprete them, (2) heeding professionally prepared weather forec

storm warnings, (3) studying marine weather and climatological sum

atlases, and (4) making use of weather charts and analyses available 

simile. 

SHIPBOARD OBSERVATIONS AS A GUIDE TO 

FUTURE WEATHER CONDITIONS 

Your observations are dependable guides in determining future wea

tions. The following factors should be considered when making a fo

Pressure and pressure changes 

Pressure changes, or a lack thereof, are very significant weather ind

approach of a low pressure or frontal system, tropical depression, st

ricane is heralded by falling pressure. A steady, persistent drop in p

mally indicates that foul weather is on the way. Be particularly wary 

sudden pressure fall of considerable magnitude. A steady and persi

pressure is indicative of a period of settled or stable weather. Steep 

rises and falls are often accompanied by strong wind. The passage o

often marked by a fall and subsequent steadying of pressure, or a fa

by a rise in pressure. High pressures accompanied by slow pressure 

ally indicate a location within or near the center of a large high pre

Wind 

Wind shifts are very meaningful, and usually foretell a change in th

during stormy conditions, the wind shifts from the east, southeast, o

to the west, northwest, or north (in the northern hemisphere), the 

should soon begin to clear. During fair weather, if the wind shifts fr

southwest, or northwest, to the east, northeast, or southeast, (in nor

sphere middle latitudes), a deterioration in weather conditions is li

cially with a falling barometer). In general (but not always), fair we

with a wind from the southwest, west, or northwest, and unsettled w

usually associated with wind from the east, southeast, or northeast (

directions are reversed for the southern hemisphere). 

NWSOH No. 1 4-1 
sequence or progression of cloud formations observed over several hou

more. In advance of storms (including mid latitude cyclones or low pre

areas, tropical depressions, storms, or hurricanes), a typical cloud progr

would be (1) high cirrus clouds several hundred miles or more in advan

the storm center, (2) if the storm is moving closer, cirrus will thicken to 

cirrostratus, and then, when the storm is only a few hundred miles away

darker altostratus, (3) If the altostratus develop into stratocumulus, or e

nimbostratus, the storm is getting closer, rain will begin to fall and wind 

should increase. The duration and intensity of storms can vary greatly; b

cloud sequences together with other indicators such as pressure and wi

tion, you will obtain a good idea of what conditions to expect. 

Vertical section of clouds ahead of a low. If a warm front is prese

it will lie along the dashed lines. 

cirrus 35,000 ft 

cirrostratus 

altostratus 

altostratus 

Cold air 

10,000 ft nimbostratus 

stratus or stratocumulus rain stratus 

stratocumulus cu

200-400 miles 

Warm air

Cumiliform clouds should also be closely watched. Cumulus with sharp 

edged cauliflower-like tops are still growing and rising vertically. Cumul

indistinct or fluffy tops have probably stopped rising and should not po

threat. Sometimes cumulus is seen to develop strongly to start with, the

out into a layer. This indicates the cloud has advanced into a temperatu

sion asociated with a high pressure area. 

If cumulus is observed to extend vertically and grow into cumulonimbu

thunderstorm with possible lightning and strong, gusty winds may be ne

When a thunderstorm enters your area, pressure may rise. This results f

downdraft of air just ahead of heavy precipitation. The downdraft may a

cause the air temperature to drop. 

Fair weather cumulus with little vertical extent are good weather clouds

indicate some instablilty close to the surface, but stable, dry conditions 

levels. High icy cirrus clouds are also indicative of fair weather (if precip

or storms are near, these clouds would not be visible). 

It has been found that halos around the sun or moon are followed by r

about 65% of the time. Halos occur as a result of refraction of light thr

NWSOH No. 1 4-2 
barometer, can be a fairly reliable indicator of inclement weather to 

Temperature and humidity 

There is a good possibility of fog formation whenever the wet bulb 

slight, or when dew point temperature is close to the wet bulb temp

fall in night-time temperature should be watched — if the wet bulb 

narrows, there is a greater likelihood of fog formation. 

Also, an increasing dew point temperature or a narrowing of the we

depression may indicate the approach of a front or storm system wi

weather. On the other hand, a low dew point temperature and larg

depression indicate very dry conditions associated with high pressu

good visibility, and generally settled weather conditions. 

Sea and swell 

The arrival or absence of swell provides a clear distinction between 

of a local thunderstorm and an approaching well developed storm 

threatening sky with increasing and thickening clouds, but without 

cannot be part of a large storm system, so any bad weather will prob

short lived. However, increasing swell from the direction of advance 

storm clouds would suggest an approaching storm with a large area 

winds. The appearance of a heavy, rolling swell often indicates the a

a tropical storm. Such swell are the remains of huge, decayed waves 

by the storm, but which travel faster than the storm. 

The presence of swell for a long time without any significant chang

conditions is difficult to interprete. A storm system may be approac

very slowly, or it may have already passed by. 

WEATHER FORECASTS AND STORM WARNINGS 

Always take advantage of professionally prepared weather forecasts 

warnings, either from the NWS or from privately operated compan

Professional forecasters obtain vast amounts of data from worldwide 

which allows them to locate and closely follow the movement of we

tems. Forecasters use numerical models which provide detailed fore

ance out 72 hours or more from run time, and which also provide u

out 144 hours (6 days) or more. 

MARINE CLIMATOLOGICAL SUMMARIES OR ATLASES 

Climatological atlases generally provide information based on cond

aged over long periods of time, and provide an indication of the ra

weather and sea conditions to be expected in a particular area. The 

Imaging and Mapping Agency (1-800-638-8972) prepares marine cl

atlases for the worlds oceans, which contain much meteorological a

graphic information. Included is information about prevailing wind

atmospheric pressure, the movement of ice, etc. See http://www.ni

NWSOH No. 1 4-3 
allowing you to do your own forecasting. Perhaps the most useful chart i

face analysis, which indicates the locations of Highs, lows, fronts, tropica

and also contains plotted surface reports, including ship reports. Your P

answer questions about using the surface and upper air weather analyses

WEATHER LORE, JINGLES AND PROVERBS 

Weather forecasting and supporting data acquisition programs (such as 

program) are a recent human advancement. Until the development of 

meteorology within the last hundred years, people relied on their own o

tions and experience to make weather predictions. It was known that ce

atmospheric conditions were likely to produce certain kinds of weather

knowledge was often put into verses or proverbs. Some of the more acc

the old sayings are shown below. All wind and compass directions are fo

northern hemisphere (especially middle latitudes), and would reverse f

southern hemisphere. 

Beware the bolts from north or west


In south or east the bolts be best


Fairly reliable in the northern hemisphere middle latitudes, where weat

erally moves from west to east. Lightning to the north or west could me

thunderstorm coming towards you. 

Rainbow to windward foul fall the day 

Rainbow to leeward, rain runs away 

A windward rainbow indicates rain upwind, so it may begin raining soon

bow behind the wind or to leeward implies the rain has probably past. 

If wooly fleece deck the heavenly way 

Be sure no rain will mar the day 

or 

If fleecy white clouds cover the heavenly way 

no rain should mar your plans that day 

Wooly fleece or fleecy white clouds refer to cumulus clouds with little ve

development (fair weather cumulus). This is sound folklore (as long as 

clouds remain flat and do not grow vertically later on). 

Mountains in the morning 

Fountains in the evening 

The mountains refer to high, billowing cumulus clouds, indicative of in

and possible development of cumulonimbus clouds and a late afternoo

evening thunderstorm. 

NWSOH No. 1 4-4 
As already indicated, a halo around the sun or moon is followed by 

weather about 65% of the time. 

Short notice, soon to pass 

Long notice, long will last 

or 

Long foretold—long last 

Short notice—soon past 

The approach of a major storm system with bad weather lasting sev

more is revealed well in advance — by cloud formations, changing 

tion, falling atmospheric pressure, the arrival of swell, etc. However

lived bad weather event, such as a local thunderstorm, might only b

short while ahead of time, such as from cumulus growing into cumu

This is, therefore, a fairly accurate jingle. 

Seagull, seagull, get out on T’sand 

We’ll never have good weather with thee on the land 

During fair weather, gulls scavenge at the waters edge or offshore. D

stormy weather, they often fly inland and scavenge at waste dumps. 

they usually don’t do this until after the storm has arrived! 

When the glass falls low 

Look out for a blow 

or 

When the wind backs, and the weather glass falls, 

Then be on your guard against gales and squalls 

Sound advice, because as already indicated, a steady, persistent fall 

pheric pressure is often a good indication of foul weather to come. 

particularly true with a windshift from the west to the east, northeas

east. 

Red sky at night, sailors delight 

Red sky in the morning, sailors take warning 

This is probably the most famous of all weather sayings, and is true 

than not. A red sky at sunset or early evening indicates clouds to th

clearing on the western horizon allowing the setting sun to be seen

weather or stormyness may have passed or be moving out. A red sky 

morning indicates clouds to the west as the sun is rising, which may 

eastward and bring bad weather with them. 

NWSOH No. 1 4-5 
Topsail sheets and halyards mind


A small, weak, frontal system will have a narrow band of associated rain

wind may be more conspicuous than rain. Stronger fronts and intense d

sions are surrounded by bad weather for considerable distances, and pr

tion should preceed the strongest wind. 

Mackeral skys and mares tails 

Make lofty ships carry low sails 

The mackeral sky is composed of cirrus and cirrocumulus clouds (which 

ble scale patterns on a mackerals back). The mares tails refer to trails o

tals blown in streaks from cirrus clouds. These clouds may appear ahead 

approaching storm or frontal system, and can indicate strong winds alo

cirrus and/or cirrocumulus thicken to cirrostratus, altostratus, and then 

stratus, stormy conditions may be on the way. Strong winds require less 

navigation in a rough sea. 

Sound traveling far and wide 

A stormy day will betide 

Low, dense, rainy, stratus and nimbostratus clouds trap sounds by preve

them from escaping into the atmosphere above. Voices or noise may ap

louder and travel further when these clouds are present. 

Frost or dew in the morning light 

Shows no rain before the night 

The formation of frost or dew requires night time cooling which usually 

only on very clear, calm nights. Such a night is usually followed by fair, s

daytime weather, so inclement weather would be unlikely. However, a w

system moving very rapidly could arrive during the day, thus interfering 

this proverb. 

First rise after low


Portends a stronger blow


The strongest, gustiest wind often does not occur until the barometer r

it’s lowest value and begins to rise. This is especially true in intense, wel

oped storm systems. Pressure gradients behind the low center can be ve

strong, giving rise to dangerous, unpredictable gales. 

NWSOH No. 1 4-6 
3-hour observation Observations taken at 3-hourly intervals, such as 0300, 

UTC, etc. 

6-hour observation Observations taken a 6-hourly intervals, such as 0000, 

UTC. These are also known as the main synoptic times

Alto- Cloud prefix meaning middle level. 

Altocumulus White or gray patch, sheet, or layer of cloud, generally w

composed of rounded masses, rolls, etc., sometimes pa

which may or may not be merged. Mainly composed of 

Altostratus Grayish or bluish sheet or layer of striated, fibrous, or u

ance, having parts thin enough to see the sun, as throu

Anemometer An instrument for measuring wind speed and direction. 

rotating cups measure speed and a vane indicates direc

Atmospheric pressure The pressure exerted by the atmosphere at a given poin

pressure at sea level. 

Bar Unit of pressure equal to 1,000,000 dynes per square c

millibars. 

Barogram A record of pressure produced by a barograph. 

Barograph A recording barometer. 

Barometer An instrument that measures atmospheric pressure. The 

meter is the standard instrument aboard ship. 

Barometric pressure The atmospheric pressure value indicated by the barom

Barometric tendency See pressure tendency. 

Beaufort wind scale A numerical scale of wind force originally designed by 

Beaufort in the early 19th century. Today, it consists of 

speed with appropriate descriptions of sea state. 

Bergy bit A piece of ice which has broken away from an iceberg, 

meters above the sea surface and 100-300 square mete

also be the remains of a melting iceberg. 

Celsius temperature Same as Centigrade temperature scale where the boilin

degrees and the freezing point is 0 degrees. 

Cirro- Cloud prefix meaning high level. 

Cirrocumulus Thin white patch, sheet, or layer of cloud without shadi

very small elements in the form of ripples, grains, etc. 

Cirrostratus Transparent, whitish cloud veil of fibrous (hairlike) or s

ance, often producing a halo. 

Cirrus Clouds of ice crystals in the form of delicate white filam

mostly white patches or narrow bands, with a fibrous ap

sheen. 

Cloud A visible aggregate of minute water droplets or ice crys

atmosphere. 

NWSOH No. 1 5-1 
Meteorological Organization International Cloud Atlas. 

Condensation	 The physical process by which a vapor becomes a liquid or a 

Crest	 The highest part of a wave. 

Cumulonimbus	 Heavy, dense cloud, with considerable vertical extent, in the f

mountain or huge tower. Part of upper portion usually, but no

smooth or fibrous. 

Cumulus	 Detached clouds, generally dense and with sharp outlines, de

vertically in the form of rising mounds, domes, or towers, of 

bulging upper part often resembles a cauliflower. The sunlit p

brilliant white; bases can be dark and nearly horizontal. 

Dew point	 The temperature to which the air must be cooled in order for 

to occur. 

Drizzle	 Fairly uniform precipitation composed exclusively of fine dro

close together. Diameter less than 0.02 inch or 0.5 millimeter

Evaporation	 The process of change from liquid water to water vapor. 

Fog	 A suspension of very small water droplets in the air, reducing 

visibility. 

Fracto- Cloud prefix meaning torn, ragged, or scattered appearance d

winds. 

Freak Wave	 A wave of great height and steepness, much higher than othe

the prevailing sea or swell system. 

Freezing Rain	 Rain that freezes on impact and forms a glaze on the ground 

objects. 

Growler	 Similiar to a bergy bit, but smaller, extending less than 1 met

sea surface and occupying an area of 20 square meters or les

Gust	 Sudden brief wind speed increase followed by lull or slacken

Hail	 Precipitation in the form of small balls or irregular pieces of 

Haze	 A suspension of very small, dry (non-liquid) particles in the a

dust, sea salt, or soot. Results in diminished visibility. Distin

from fog by its dryness. 

Hectopascal	 A unit of measure of atmospheric pressure equal to 100 newt

square meter. It is the numerical equivalant of a millibar. 

Horizon	 The distant line along which the sea surface, or the earth, and 

appear to meet. It is the actual lower boundary of the observe

upper outline of terrestrial objects. 

Hygrometer	 Instrument to measure humidity. The wet- and dry-bulb sling 

ter is a type of hygrometer. 

Iceberg	 A piece of a glacier which has broken off and is floating in th

Ice pellets	 Pellets or small pieces of ice, with a diameter of 5 millimeters 

which bounce on impact. 

NWSOH No. 1 5-2	 
Knot One nautical mile per hour or approximately .5 meters p

Land Ice Any ice of land origin, from the freezing of fresh water o

of snow, such as an iceberg. 

Lenticular A type of cloud formed in the ascending portion of an a

remains stationary while the air blows through it. 

Main synoptic times The times of 0000, 0600, 1200, and 1800 UTC. Also kn

dard synoptic times. 

Millibar One one-thousandth of a bar. Numerically the same as 

weight of an average column of air at sea level is 1016 

Nautical mile 1852 meters, or 6080.2 feet. 

Nimbostratus Gray cloud layer, often dark, thick enough to block out t

appears diffuse by falling precipitation. 

Obscured sky The condition when the entire sky is hidden by surface-

phenomena. 

Okta Used for the measurement of total cloud cover. One okt

the equivalent of 1/8 of the sky covered with cloud. 

Period See wave period. 

PMO Port meteorological officer. 

Precipitation All types of condensed water vapor, whether liquid, free

which fall out of the atmosphere to the earth’s surface. 

Pressure See atmospheric pressure. 

Pressure change The net difference between the pressure at the beginnin

specified interval of time. 

Pressure characteristic The indication of how the pressure has been changing 

period preceding an observation; i.e. decreasing then in

pressure, or lower than 3-hours ago. 

Pressure tendency The character and amount of atmospheric pressure cha

hour period preceding an observation. 

Psychrometer An instrument for measuring the moisture content of th

wet- “and” dry- bulb thermometer; a type of hygromete

Rain Liquid precipitation that remains in the liquid state upo

ground or other exposed objects. 

Remarks Plain language data added after the last group of the we

report significant information not provided for in the ma

report. 

Ripple A small wavelet which forms at wind speeds of 1-3 kno

Saturation The stage where the water content of the atmosphere re

mum possible under the existing environmental conditi

Sea Locally generated waves produced by the wind, and des

period and height. 

Sea ice Ice formed from the freezing of the sea surface. 

NWSOH No. 1 5-3 
partially frozen. Same as ice pellets. 

Sling psychrometer A type of hygrometer with two thermometers, which is whirle

mine air and wet bulb temperatures. The bulb of one is kept m

piece of wet muslin. 

Snow Precipitation of ice crystals, mostly branched in star shapes. 

Snow grains Very small, white, opaque grains of ice, with a diameter of les

millimeter. Frozen drizzle. 

Snow pellets White, opaque grains of ice, with a diameter of 2-5 millimete

Special observation An unscheduled or special observation taken to report signifi

changes in one or more of the observed elements since the la

observation. 

Squall A sudden increase in wind speed of at least 15 knots which i

at 20 knots or more for at least 1 minute. 

Standard barometer A barometer of very high accuracy used to calibrate other bar

NWS PMOs use hand- held standard digital barometers to ca

board barometers. 

Standard synoptic times The times of 0000, 0600, 1200, and 1800 UTC. Also known a

synoptic times. 

Station pressure The atmospheric pressure at barometer height, normally on t

Barometers aboard NWS Voluntary Observing Ships are calib

possible, to read sea-level pressure. 

Storm Sustained wind of 48-55 knots (defined by the WMO as Beau

Force 10). 

Strato- Cloud prefix referring to cloud sheets or layers. 

Stratocumulus Gray or whitish patch, sheet, or layer of cloud, almost always 

parts, with non- fibrous rounded masses or rolls, which may 

be merged. 

Stratus Generally gray cloud layer with a fairly uniform base, which m

drizzle or snow grains. 

Surface observation Surface weather observations taken in accordance with World 

Meteorological Organization regulations, containing those we

ments most important for forecasting and later use. 

Swell Ocean waves which have travelled beyond the generating area

longer periods and are more regular than seas. 

Synoptic code Rules and procedures established by the World Meteorologic

Organization for encoding weather observations. 

Temperature A measure of the hotness or coldness of the air as measured 

able instrument, using a defined temperature scale. 

Trough The lowest part of a wave. 

True direction Direction measured in degrees clockwise from true north, wh

0 degrees. 

NWSOH No. 1 5-4 
and identified. 

Visibility reference Selected objects at known distances used to determine 

Voluntary Observing Program of the WMO and NWS to manage weather repo

Ship (VOS) program by ships at sea and on the Great Lakes. 

Water vapor The gaseous form of water. 

Wave height Distance from trough to crest, averaged for the better fo

center of the wave group. 

Wave length Distance from trough to trough or crest to crest for adja

Wave period Time, in seconds, for the passage of successive wave c

computed as an average value for several waves. 

Weather The individual and combined atmospheric phenomena 

the local atmospheric conditions at the time of observat

Whitecap The breaking crest of a wave, usually white and frothy. 

Wind The horizontal motion of the air past a given point. 

Wind character The measure of the variability of the wind speed in term

squalls. 

Wind direction The true direction from which the wind is blowing at a g

Wind shift A change in the average wind direction of 45 ̊ or more w

in less than 15 minutes with wind speeds greater than 1

Wind speed The rate at which the air is moving horizontally past a g

Vessels usually estimate wind speed by relating the stat

Beaufort Scale of wind force. 

NWSOH No. 1 5-5 
NWSOH No. 1 5-6 
WEATHER MAP BASES

N. Atlantic–U.S. Intercoastal

N. Pacific–U.S. Intercoastal

S. Atlantic–U.S. Intercoastal

S. Pacific–Indian Ocean

WALL CHARTS

Sea State Poster

Cloud Poster 

Explanation of the Daily Weather Map

BROCHURE

PMO/VOS Program

Guide to Sea State, Wind and Clouds

Observing Forms and Supplies 

BOOKLETS AND MANUALS 

NWS Observing Handbook No. 1 

World Wide Marine Radiofacsimile Broadcast Schedules 

Guide to Sea State, Wind and Clouds 

OBSERVING FORMS 

Ship’s Weather Observations 

Barogram 

Pre-Addressed Envelopes 

Pre-Addressed Diskette Mailers & Archive Diskettes 

NWSOH No. 1 A-1 
NWSOH No. 1 A-2 
Conversion Factors and Equivalents 

LENGTH 

1 foot = .3048 meters 

1 centimeter = 10 millimeters = .394 inches = .01 meters 

1 meter = 100 centimeters = 3.2808 feet = 39.37 inches = 1.09 yards = .5

1 kilometer = 1000 meters = 3280.8 feet = .54 nautical miles = .621 statu

1 degree latitude = 111.1 kilometers 

1 statute mile = 1.6093 kilometers 

SPEED 

1 knot (nautical mile/hour) = 1.15 statute miles/hour = .51 meters/sec 

1 meter/sec = 2.24 statute miles/hour = 1.94 knots 

1 centimeter/second = 1.97 feet per minute 

TEMPERATURE 

Degrees Celsius = Degrees Centigrade 

Celsius = 5/9(Fahrenheit - 32) 

or 

Celsius = (Fahrenheit - 32)/1.8 

Fahrenheit = 1.8(Celsius) + 32 

or 

Fahrenheit = 1.8(Celsius + 40) - 40 

PRESSURE 

1 millimeter mercury = .03937 inches = 1.3332 millibars 

1 inch mercury = 25.4 millimeters = 33.8640 millibars 

1 millibar = .02953 inches = .75006 millimeters 

millibars = inches x 33.865 

inches = millibars/33.864 

Standard Atmosphere: vertical pressure change is .037 millibars/foot 

(.1214 millibars/meter) 

AREA 

1 square centimeter = .155 square inches 

1 square meter = 10.8 square feet 

1 square kilometer = .386 square statute miles = .292 square nautical m

NWSOH No. 1 B-1 
°F. 0.0 

°C. 

0.1 

°C. 

0.2 

°C. 

0.3 

°C. 

0.4 

°C. 

0.5 

°C. 

0.6 

°C. 

0.7 

°C. 

0.8 

°C. 

+110 +43.3 +43.4 +43.4 +43.6 +43.6 +43.6 +43.7 +43.7 +43.8 +

109 42.8 42.8 42.9 42.9 43.0 43.1 43.1 43.2 43.2 

108 42.2 42.3 42.3 42.4 42.4 42.5 42.6 42.6 42.7 

107 41.7 41.7 41.8 41.8 41.9 41.9 42.0 42.1 42.1 

106 41.1 41.2 41.2 41.3 41.3 41.4 41.4 41.5 41.6 

+105 +40.6 +40.6 +40.7 +40.7 +40.8 +40.8 +40.9 +40.9 +41.0 +

104 40.0 40.1 40.1 40.2 40.2 40.3 40.3 40.4 40.4 

103 39.4 39.5 39.6 39.6 39.7 39.7 39.8 39.8 39.9 

102 38.9 38.9 39.0 39.1 39.1 39.2 39.2 39.3 39.3 

101 38.3 38.4 38.4 38.5 38.6 38.6 38.7 38.7 38.8 

+100 +37.8 +37.8 +37.9 +37.9 +38.0 +38.1 +38.1 +38.2 +38.2 +

99 37.2 37.3 37.3 37.4 37.4 37.5 37.6 37.6 37.7 

98 36.7 36.7 36.8 36.8 36.9 36.9 37.0 37.1 37.1 

97 36.1 36.2 36.2 36.3 36.3 36.4 36.4 36.5 36.6 

96 35.6 35.6 35.7 35.7 35.8 35.8 35.9 35.9 36.0 

+95 +35.0 +35.1 +35.1 +35.2 +35.2 +35.3 +35.3 +35.4 +35.4 +

94 34.4 34.5 34.6 34.6 34.7 34.7 34.8 34.8 34.9 

93 33.9 33.9 34.0 34.1 34.1 34.2 34.2 34.3 34.3 

92 33.3 33.4 33.4 33.5 33.6 33.6 33.7 33.7 33.8 

91 32.8 32.8 32.9 32.9 33.0 33.1 33.1 33.2 33.2 

+90 +32.2 +32.3 +32.3 +32.4 +32.4 +32.5 +32.6 +32.6 +32.7 +

89 31.7 31.7 31.8 31.8 31.9 31.9 32.0 32.1 32.1 

88 31.1 31.2 31.2 31.3 31.3 31.4 31.4 31.5 31.6 

87 30.6 30.6 30.7 30.7 30.8 30.8 30.9 30.9 31.0 

86 30.0 30.1 30.1 30.2 30.2 30.3 30.3 30.4 30.4 

+85 +29.4 +29.5 +29.6 +29.6 +29.7 +29.7 +29.8 +29.8 +29.9 +

84 28.9 28.9 29.0 29.1 29.1 29.2 29.2 29.3 29.3 

83 28.3 28.4 28.4 28.5 28.6 28.6 28.7 28.7 28.8 

82 27.8 27.8 27.9 27.9 28.0 28.1 28.1 28.2 28.2 

81 27.2 27.3 27.3 27.4 27.4 27.5 27.6 27.6 27.7 

+80 +26.7 +26.7 +26.8 +26.8 +26.9 +26.9 +27.0 +27.1 +27.1 +

79 26.1 26.2 26.2 26.3 26.3 26.4 26.4 26.5 26.6 

78 25.6 25.6 25.7 25.7 25.8 25.8 25.9 25.9 26.0 

77 25.0 25.1 25.1 25.2 25.2 25.3 25.3 25.4 25.4 

76 24.4 24.5 24.6 24.6 24.7 24.7 24.8 24.8 24.9 

+75 +23.9 +23.9 +24.0 +24.1 +24.1 +24.2 +24.2 +24.3 +24.3 +

74 23.3 23.4 23.4 23.5 23.6 23.6 23.7 23.7 23.8 

73 22.8 22.8 22.9 22.9 23.0 23.1 23.1 23.2 23.3 

72 22.2 22.3 22.3 22.4 22.4 22.5 22.6 22.6 22.7 

71 21.7 21.7 21.8 21.8 21.9 21.9 22.0 22.1 22.1 

+70 +21.1 +21.2 +21.2 +21.3 +21.3 +21.4 +21.4 +21.5 +21.6 +

69 20.6 20.6 20.7 20.7 20.8 20.8 20.9 20.9 21.0 

68 20.0 20.1 20.1 20.2 20.2 20.3 20.3 20.4 20.4 

67 19.4 19.5 19.6 19.6 19.7 19.7 19.8 19.8 19.8 

66 18.9 18.9 19.0 19.1 19.1 19.2 19.2 19.3 19.3 

+65 +18.3 +18.4 +18.4 +18.5 +18.6 +18.6 +18.7 +18.7 +18.8 +

64 17.8 17.8 17.9 17.9 18.0 18.1 18.1 18.2 18.2 

63 17.2 17.3 17.3 17.4 17.4 17.5 17.6 17.6 17.7 

62 16.7 16.7 16.8 16.8 16.9 16.9 17.0 17.1 17.1 

61 16.1 16.2 16.2 16.3 16.3 16.4 16.4 16.5 16.6 

NWSOH No. 1 B-2 
°F. 0.0 

°C. 

0.1 

°C. 

0.2 

°C. 

0.3 

°C. 

0.4 

°C. 

0.5 

°C. 

0.6 

°C. 

0.7 

°C. 

0

°C

+60 +15.6 +15.6 +15.7 +15.7 +15.8 +15.8 +15.8 +15.9 +16

59 15.0 15.1 15.1 15.2 15.2 15.3 15.3 15.4 15

58 14.4 14.5 14.6 14.6 14.7 14.7 14.8 14.8 14

57 13.9 13.9 14.0 14.1 14.1 14.2 14.2 14.3 14

56 13.3 13.4 13.4 13.5 13.6 13.6 13.7 13.7 13

+55 +12.8 +12.8 +12.9 +12.9 +13.0 +13.1 +13.1 +13.2 +13

54 12.2 12.3 12.3 12.4 12.4 12.5 12.6 12.6 12

53 11.7 11.7 11.8 11.8 11.9 11.9 12.0 12.1 12

52 11.1 11.2 11.2 11.3 11.3 11.4 11.4 11.5 11

51 10.6 10.6 10.7 10.7 10.8 10.8 10.9 10.9 11

+50 +10.0 +10.1 +10.1 +10.2 +10.2 +10.3 +10.3 +10.4 +10

49 9.4 9.5 9.6 9.6 9.7 9.7 9.8 9.8 9

48 8.9 8.9 9.0 9.1 9.1 9.2 9.2 9.3 9

47 8.3 8.4 8.4 8.5 8.6 8.6 8.7 8.7 8

46 7.8 7.8 7.9 7.9 8.0 8.1 8.1 8.2 8

+45 +7.2 +7.3 +7.3 +7.4 +7.4 +7.5 +7.6 +7.6 +7

44 6.7 6.7 6.8 6.8 6.9 6.9 7.0 7.1 7

43 6.1 6.2 6.2 6.3 6.3 6.4 6.4 6.5 6

42 5.6 5.6 5.7 5.7 5.8 5.8 5.9 5.9 6

41 5.0 5.1 5.1 5.2 5.2 5.3 5.3 5.4 5

+40 +4.4 +4.5 +4.6 +4.6 +4.7 +4.7 +4.8 +4.8 +4

39 3.9 3.9 4.0 4.1 4.1 4.2 4.2 4.3 4

38 3.3 3.4 3.4 3.5 3.6 3.6 3.7 3.7 3

37 2.8 2.8 2.9 2.9 3.0 3.1 3.1 3.2 3

36. 2.2 2.3 2.3 2.4 2.4 2.5 2.6 21.6 2

+35 +1.7 +1.7 +1.8 +1.8 +1.9 +1.9 +2.0 +2.1 +2

34 +1.1 +1.2 +1.2 +1.3 +1.3 +1.4 +1.4 +1.5 +1

33 +0.6 +0.6 +0.7 +0.7 +0.8 +0.8 +0.9 +0.9 +1

32 0.0 +0.1 +0.1 +0.2 +0.2 +0.3 +0.3 +0.4 +0

31 -0.6 -0.5 -0.4 -0.4 -0.3 -0.3 -0.2 -0.2 -0

+30 -1.1 -1.1 -1.0 -0.9 -0.9 -0.8 -0.8 -0.7 -0

29 -1.7 -1.6 -1.6 -1.5 -1.4 -1.4 -1.3 -1.3 -1

28 -2.2 -2.2 -2.1 -2.1 -2.0 -1.9 -1.9 -1.8 -1

27 -2.8 -2.7 -2.7 -2.6 -2.6 -2.5 -2.4 -2.4 -2

26 -3.3 -3.3 -3.2 -3.2 -3.1 -3.1 -3.0 -2.9 -2

+25 -3.9 -3.8 -3.8 -3.7 -3.7 -3.6 -3.6 -3.5 -3

24 -4.4 -4.4 -4.3 -4.3 -4.2 -4.2 -4.1 -4.1 -4

23 -5.0 -4.9 -4.9 -4.8 -4.8 -4.7 -4.7 -4.6 -4

22 -5.6 -5.5 -5.4 -5.4 -5.3 -5.3 -5.2 -5.2 -5

21 -6.1 -6.1 -6.0 -5.9 -5.9 -5.8 -5.8 -5.7 -5

+20 -6.7 -6.6 -6.6 -6.5 -6.4 -6.4 -6.3 -6.3 -6

19 -7.2 -7.2 -7.1 -7.1 -7.0 -6.9 6.9 -6.8 -6

18 -7.8 -7.7 -7.7 -7.6 -7.6 -7.5 -7.4 -7.4 -7

17 -8.3 -8.3 -8.2 -8.2 -8.1 -8.1 -8.0 -7.9 -7

16 -8.9 -8.8 -8.8 -8.7 -8.7 -8.6 -8.6 -8.5 -8

+15 -9.4 -9.4 -9.3 -9.3 -9.2 -9.2 -9.1 -9.1 -9

14 -10.0 -9.9 -9.9 -9.8 -9.8 -9.7 -9.7 -9.6 -9

13 -10.6 -10.5 -10.4 -10.4 -10.3 -10.3 -10.2 -10.2 -10

12 -11.1 -11.1 -11.0 -10.9 -10.9 -10.8 -10.8 -10.7 -10

11 -11.7 -11.6 -11.6 -11.5 -11.4 -11.4 -11.3 -11.3 -11

NWSOH No. 1 B-3 

Interpretation of Weather Map Symbols 

CODE FIGURES AND SYMBOLS 

Present Weather ww, Cloud Types CLCMCH, Past Weather W1W2, Sky Cover N, Pressure Ch

SYMBOLS FOR FRONTS, ISOBARS, ETC. 

SAMPLE WIND PLOT 

NWSOH No. 1 C-1 
27 96 24

CALL

21 

1372020604181008241504

2 

MIDDLE AND HIGH CLOUD TYPE (Cm, Ch)

SHIP’S COURSE AND AVERAGE SPEED (Dsvs) (N) TOTAL AMOUNT OF CLOUDS


(TTT) TEMPERATURE (Celsius)
 BAROMETRIC PRESSURE (Millibars and tenths) (PPP)

(VV) VISIBILITY AND (WW) PRESENT WEATHER 3 HOUR PRESSURE TENDENCY AND PRESSURE CHANGE (appp) 

(TdTdTd) DEW POINT TEMPERATURE SEA WAVES INDICATOR, PERIOD (Secs.), HEIGHT (Half Meters)

VESSEL CALL SIGN (2PwPwHwHw) 

(TwTwTw) SEA SURFACE TEMPERATURE PRIMARY SWELL (Direction, Period, Height) (dw1dw1Pw1Pw1Hw1Hw1

(ddff) WIND DIRECTION AND SPEED SECONDARY SWELL (Direction, Period, Height) (dw2dw2Pw2Pw2Hw2H

Low Cloud Type (CL) 

SAMPLE MESSAGE DECODED:Visibility 2 miles; Wind from 230°, 25 knots; 27°C, Dew Point Temperature 24°C, Sea Level Pressure1013.7 millibars, Pressure falling, then rising. Net 3 Hour pressure change minus 2 millibars, Present Weather—rain showers, Past Weather—showers and drizzle, Fraction of sky cover by CL cloud 3 

eighths, CL cloud cumulus, CW cloud altocumulus, CH cloud cirrus, Ships course South, average speed 

8 knots, Sea Surface Temperature 21°C, Sea Waves Period 6 seconds, height 2 meters (1 half meters),Primary Swell from 180° (South), period 10 seconds, height 4 meters, Secondary Swell running from240°

period 15 seconds

height 2 meters

total cloud amount 4 eighths

NWSOH No. 1 C-2 
High Seas Responsibility


MPC 

HNL 

TPC 

MPC 

TPC 

HNL 

— National Meteorologica

Camp Springs, MD 

— National Hurricane Cen

— Weather Service Forec

Honolulu, HI 

20° 

0° 

20° 

40° 

60° 

180° 160° 140° 

120° 

60° 

100° 80° 

NWSOH No. 1 D-1 
LEGEND 

MFL — Miami, Fl 

ILM 

HFO — Honolulu, HI 

EKA — Eureka, Ca 

DLH — Duluth, Mn 

DTX — Detroit, Mi 

BRO — Brownsville, Tx 

CRP — Corpus Christi, Tx 

HGX — Houston/Galveston, Tx 

LCH — Lake Charles, LA 

LIX — New Orleans/Slidell, LA 

MOB — Mobile, Al 

TAE — Tallahassee, Fl 

TBW — Tampa Bay, Fl 

MLB — Melbourne, Fl 

JAX — Jacksonville, Fl 

CHS — Charleston, Sc 

— Wilmington, Nc 

MHX — Morehead City, Nc 

AKQ — Wakefield, Va 

LWX — Baltimore/Washington DC 

PHI — Philadelphia/Mt. Holly 

OKX — New York City 

BOX — Boston, Ma 

PTA — Portland, Me 

AFG — Fairbanks, Ak 

AFC — Anchorage, Ak 

AJK — Juneau, Ak 

MPC — Marine Prediction Center 

SGX — San Diego, Ca 

LOX — Los Angeles/Oxnard, Ca 

MTR — Monterey, Ca 

MFR — Medford, Or 

PQR — Portland, Or 

SEW — Seattle, Wa 

Great Lakes Offices: 

MQT — Marquette, Mi 

APX — Gaylord, Mi 

GRB — Green Bay, Wi 

MKX — Milwaukee, Wi 

LOT — Chicago, Il 

GRR — Grand Rapids, Mi 

CLE — Cleveland, Oh 

BUF — Buffalo, NY 

NWSOH No. 1 D-2 
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This completely redesigned handbook has bee

possible. 

Ship Program. 

U.S. DEPARTME N T OF COMMERCE 

NAT O I NAL OCEANIC AND AT M OSPHERIC ADMINISTRA T OI N 

treasured by meteorologists as invaluable in th

preparation of marine weather forecasts an

storm warnings. They are also of critical impo

tance in identifying and tracking weather sy

tems in their worldwide movement. 

prepared to help you observe, code, and repo

weather — as easily, quickly, and accurately a

The National Weather Service thanks ship

officers for their enormous effort and dedicatio

as weather observers in the Voluntary Observin

Only YOU know the weather at your positio

Please report it at 00, 06, 12, and 18 UTC to th

National Weather Service.