Number range CHAPTERTropical Cyclone Report

Tropical Storm Erin

(AL052007)

15-17 August 2007

Richard D. Knabb

National Hurricane Center

7 April 2008

Erin was a tropical storm that formed in the Gulf of Mexico and made
landfall along the Texas coast as a tropical depression. The tropical
cyclone directly caused nine fatalities and its remnants caused seven
more, mostly as a result of inland flooding due to heavy rainfall. Erin
will also be remembered for its unusual, brief strengthening, although
not as a tropical cyclone, over Oklahoma.

a.  Synoptic History

Erin formed in association with a tropical wave that departed the west
coast of Africa on 3 August. The wave moved uneventfully across the
tropical Atlantic and eastern Caribbean Sea during the following week or
so. Eventually a broad surface low formed in the western Caribbean in
association with the wave on 12 August. Development was limited in the
Caribbean, as the low was influenced by vertical wind shear south of an
upper-level low centered over the eastern Gulf of Mexico. The
upper-level low moved quickly westward during 13-14 August, allowing
vertical wind shear to decrease over the southeastern Gulf as the
surface low moved into that area. Thunderstorm activity associated with
the surface low increased, and Dvorak classifications were initiated at
1800 UTC 13 August. The system gradually gained some organization over
the warm waters of the Gulf, and it became a tropical depression at
about 0000 UTC 15 August while centered roughly 375 n mi east-southeast
of Brownsville, Texas. The "best track" chart of the tropical cyclone's
path is given in Fig. 1, with the wind and pressure histories shown in
Figs. 2 and 3, respectively. The best track positions and intensities
are listed in Table 1.

Moving northwestward to the south of a large deep-layer ridge over the
southern United States, the cyclone became a tropical storm with maximum
winds of 35 kt by 1800 UTC 15 August while centered about 180 n mi east
of Brownsville. Bands of heavy rain began moving ashore along nearly the
entire coast of Texas at about that time. Sprawling and not very well
organized, however, Erin did not strengthen any further over the Gulf,
and it barely maintained tropical storm status early on 16 August. The
center of Erin made landfall at about 1030 UTC that day on San Jose
Island, Texas (just north of Port Aransas and about 30 n mi
east-northeast of Corpus Christi). By that time Erin had weakened to a
tropical depression with maximum winds of 30 kt. The depression
continued northwestward and inland, and degenerated to a remnant low by
1200 UTC 17 August when it was centered about 50 n mi south of San
Angelo, Texas. The remnant low turned northward over extreme western
Texas on 18 August around the western periphery of the ridge over the
southeastern United States. Upon reaching the northwestern extent of the
ridge, the system turned northeastward and entered southwestern Oklahoma
shortly after 0000 UTC 19 August. The remnant low had occasionally
produced some heavy rainfall over Texas during the preceding 36 hours,
but the convection was not sufficiently persistent and organized to
designate the system as a tropical depression during that period.

As the surface low moved generally east-northeastward over Oklahoma
early on 19 August, the associated thunderstorm activity abruptly
increased as the low interacted with an eastward-moving upper-level
shortwave trough. During an approximately six-hour period that morning,
sustained surface winds as strong as about 50 kt were observed at
several locations in western and central Oklahoma, with isolated gusts
as strong as about 70 kt. The system's organization also became
dramatically enhanced, with an eye-like feature readily discernible in
WSR-88D radar imagery between about 0800 and 1300 UTC as the center of
the low passed just north of downtown Oklahoma City (Fig. 4 shows a
radar image at 1200 UTC). This episode was short-lived, however, and the
eye-like feature quickly dissipated after 1300 UTC. The thunderstorm
activity and strong winds had already begun to weaken by that time, as
the upper-level shortwave trough proceeded eastward and away from the
surface low. The surface circulation dissipated shortly after 1800 UTC
19 August over northeastern Oklahoma, but remnant moisture continued
northeastward into Missouri.

While the system\'s structure, particularly its convective organization
as seen on radar, resembled and had some characteristics of a tropical
storm for a few hours on 19 August, the prevailing view from the
Hurricane Specialists at the National Hurricane Center (NHC) is that the
system was not a tropical cyclone[^1] over Oklahoma. The phrase
"organized deep convection" in the NHC tropical cyclone definition has
both spatial and temporal components, meaning that a tropical cyclone
must produce deep convection over some period of time.  While it is a
subjective determination, in this case the deep convection is judged to
have lasted an insufficient period of time to classify the system as a
tropical cyclone. The limited duration of the convection also appears to
be indicative of the physical mechanisms that caused the low to briefly
strengthen. It is speculated that the upper-level shortwave trough
forced the deep convection to increase via upper-level difluence, while
briefly superimposed above the surface low that provided a focus for
low-level confluence. The upper-level forcing was apparently a dominant
mechanism, which is in contrast to tropical cyclones that are maintained
primarily by extraction of heat energy from the ocean. Since the system
was clearly non-frontal, designating it as an extratropical cyclone[^2]
is also not the most appropriate solution. In addition, the prevailing
view among the NHC's Hurricane Specialists is that the system's duration
over Oklahoma on 19 August was also too short to classify it as a
subtropical cyclone[^3]. Given all of the considerations described
above, the system is simply designated as a "low" by NHC on 19 August.

b.  Meteorological Statistics

    Observations in Erin (Figs. 2 and 3) include satellite-based Dvorak
    technique intensity estimates from the Tropical Analysis and
    Forecast Branch (TAFB) and the Satellite Analysis Branch (SAB), as
    well as observations from two flights of the 53^rd^ Weather
    Reconnaissance Squadron of the U. S. Air Force Reserve Command, and
    one flight of a NOAA WP-3D aircraft. Data and imagery from NOAA
    polar-orbiting satellites, the NASA Tropical Rainfall Measuring
    Mission (TRMM), the NASA QuikSCAT, and Defense Meteorological
    Satellite Program (DMSP) satellites, among others, were also useful
    in tracking Erin. WSR-88D radar data from sites in Texas and
    Oklahoma were very useful for analyzing the system at landfall and
    thereafter, as were numerous surface observations including those
    collected by the Oklahoma Mesonet. Selected, significant surface
    observations from land stations and data buoys are given in Table 2,
    including data in Oklahoma from 19 August when Erin was no longer a
    tropical cyclone. No ship reports of winds of tropical storm force
    were received in association with Erin.

    Erin's maximum intensity of 35 kt as a tropical cyclone is supported
    by aircraft reconnaissance data and Dvorak estimates. The NOAA
    aircraft at an altitude of about 1500 ft measured a flight-level
    wind of 44 kt, corresponding to about 35 kt at the surface, at 1445
    UTC 15 August. The Air Force aircraft later measured winds of 43 kt
    at the same flight level at about 0100 UTC 16 August. Dvorak
    intensity estimates were at least 35 kt, occasionally reaching 45
    kt, between 1800 UTC 15 August and 0600 UTC the next day, which is
    the period during which Erin has been designated as a tropical storm
    in the best track.

    The maximum intensity of the low over Oklahoma is set to 50 kt at
    0600 UTC 19 August based on surface observations. An Oklahoma
    Mesonet site located seven miles west of Watonga (about 50 n mi
    northwest of Oklahoma City), reported sustained winds (5-minute
    average) of 47 kt near 0725 UTC, with sustained winds of gale force
    occurring there much of the time between 0600 and 0800 UTC. Also, at
    0725 UTC, this station measured a surface pressure estimated to be
    equivalent to 999 mb at sea level, so the minimum central pressure
    was likely lower than that observation and is set to 995 mb at 0600
    UTC in the best track. Nearby, a sustained wind of 42 kt, with a
    gust to 71 kt, was measured at Watonga Airport (an AWOS site) at
    0754 UTC, and the station stopped reporting after that time. A
    little earlier, the Oklahoma Mesonet site at Fort Cobb (about 50 n
    mi west-southwest of Oklahoma City) reported a sustained wind of 43
    kt (also a 5-minute average). Several other observing sites in the
    eastern semicircle of the circulation, within about 45 n mi of the
    center, measured sustained winds of 35-40 kt at times between about
    0500 UTC until almost 1200 UTC; the strongest winds at selected
    sites are listed in Table 2.

Erin and its remnants brought heavy rains to portions of southeastern,
south-central, and western Texas, portions of Oklahoma, and portions of
southern Missouri. Storm-total rainfall amounts of 3-7 in were common in
these areas, with some locations receiving more than 10 in (Table 2 and
Fig. 5). Erin added to the effects of the flooding that had already
occurred within the two prior weeks in the Nueces River basin south and
west of San Antonio, Texas.

Approximately three feet of storm surge occurred in the Galveston area
on the day of Erin's landfall.

A weak tornado was observed in the Houston area on 16 August. Following
Erin's tropical cyclone phase, six tornadoes were reported in Oklahoma
on 18-19 August.

c.  Casualty and Damage Statistics

    Erin directly caused nine fatalities in parts of southern and
    western Texas while the system was still a tropical cyclone.
    Thereafter, the remnants of Erin directly caused seven additional
    fatalities (six in Oklahoma, and one in Missouri). Most of the 16
    total fatalities were due to inland flooding induced by heavy rains,
    with several of these occurring when occupants drowned in
    automobiles swept away by floodwaters. On the day of landfall in the
    Houston, Texas area, several bayous reached flood stage, numerous
    roads were flooded, and more than 400 homes and 40 businesses were
    inundated. Minor beach erosion occurred in Galveston and Freeport,
    Texas. Significant damages occurred on 19 August in some communities
    northwest of Oklahoma City, where several homes were flooded, and
    strong winds damaged some mobile homes and downed several trees and
    power lines. The Property Claim Services of the Insurance Services
    Office did not provide damage cost estimates for the United States
    for Erin, since the estimates did not surpass their threshold of
    \$25 million.

d.  Forecast and Warning Critique

    The genesis of Erin was anticipated rather well. The system that
    eventually became Erin was first mentioned in the NHC Tropical
    Weather Outlook a little more than three days prior to genesis.
    During the next couple of days, while the incipient system was over
    the Caribbean Sea, the Outlooks correctly indicated that conditions
    were not favorable for development at the time but were expected to
    become more favorable over the Gulf of Mexico. The potential for the
    formation of a tropical depression was then mentioned explicitly
    beginning about 32 hours before the depression formed over the Gulf.

    A verification of official and guidance model track forecasts is
    given in Table 3. Very few forecasts can be verified since Erin was
    a tropical cyclone for only about 54 hours, with the number of
    forecasts ranging from seven at 12 h to just two at 48 h. Average
    official track errors for Erin were generally a little greater than
    the average long-term official track errors, but they were smaller
    than the errors from most of the objective models including the
    consensus guidance. The official forecasts were biased slow and at
    times slightly south of the actual track. Among the individual
    dynamical models that were available, the GFDL and HWRF had the
    smallest errors.

    As for the track forecasts, very few intensity forecasts could be
    verified. Average official intensity errors for these forecasts were
    generally smaller than the long-term average errors, but were
    noticeably larger than the errors for the intensity consensus ICON
    (Table 4). The official intensity forecasts were biased high, in
    part since the official track forecasts were biased slow and implied
    that Erin would have more time over water to strengthen.

    Table 5 summarizes the coastal watches and warnings issued for Erin.

e.  Acknowledgments

Oklahoma Mesonet data are provided courtesy of the Oklahoma Mesonet, "a
cooperative venture between Oklahoma State University and The University
of Oklahoma and supported by the taxpayers of Oklahoma." Appreciation is
also extended to Doug Speheger at the National Weather Service Forecast
Office in Norman, Oklahoma for providing radar and surface observations
and for his analysis of this event.

Number range CHAPTERTable 1. Best track for Tropical Storm Erin, 15-17
August 2007.

+-----------+--------+---------+---------+-----------+----------------+
| Date/Time | La     | Lo      | P       | Wind      | Stage          |
|           | titude | ngitude | ressure | Speed     |                |
| (UTC)     |        |         |         |           |                |
|           | (°N)   | (°W)    | (mb)    | (kt)      |                |
+-----------+--------+---------+---------+-----------+----------------+
| 15 / 0000 | 23.7   | 90.7    | 1006    | 25        | tropical       |
|           |        |         |         |           | depression     |
+-----------+--------+---------+---------+-----------+----------------+
| 15 / 0600 | 24.5   | 91.8    | 1006    | 25        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 15 / 1200 | 25.2   | 92.9    | 1005    | 30        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 15 / 1800 | 25.8   | 94.0    | 1004    | 35        | tropical storm |
+-----------+--------+---------+---------+-----------+----------------+
| 16 / 0000 | 26.3   | 95.2    | 1003    | 35        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 16 / 0600 | 27.2   | 96.2    | 1005    | 35        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 16 / 1200 | 28.1   | 97.1    | 1006    | 30        | tropical       |
|           |        |         |         |           | depression     |
+-----------+--------+---------+---------+-----------+----------------+
| 16 / 1800 | 28.8   | 97.8    | 1006    | 25        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 17 / 0000 | 29.4   | 98.6    | 1006    | 25        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 17 / 0600 | 30.0   | 99.5    | 1007    | 25        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 17 / 1200 | 30.5   | 100.6   | 1008    | 20        | remnant low    |
+-----------+--------+---------+---------+-----------+----------------+
| 17 / 1800 | 31.1   | 101.4   | 1008    | 20        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 18 / 0000 | 31.8   | 101.8   | 1008    | 20        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 18 / 0600 | 32.5   | 101.8   | 1008    | 20        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 18 / 1200 | 33.2   | 101.5   | 1008    | 20        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 18 / 1800 | 34.0   | 101.0   | 1007    | 20        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 19 / 0000 | 34.8   | 100.1   | 1004    | 25        | low            |
+-----------+--------+---------+---------+-----------+----------------+
| 19 / 0600 | 35.6   | 98.8    | 995     | 50        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 19 / 1200 | 35.6   | 97.7    | 1002    | 35        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 19 / 1800 | 35.9   | 96.5    | 1007    | 20        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 20 / 0000 |        |         |         |           | dissipated     |
+-----------+--------+---------+---------+-----------+----------------+
| 16 / 0000 | 26.3   | 95.2    | 1003    | 35        | minimum        |
|           |        |         |         |           | pressure and   |
|           |        |         |         |           | maximum winds  |
|           |        |         |         |           | as a tropical  |
|           |        |         |         |           | cyclone        |
+-----------+--------+---------+---------+-----------+----------------+
| 16 / 1030 | 28.0   | 96.9    | 1006    | 30        | landfall at    |
|           |        |         |         |           | San Jose       |
|           |        |         |         |           | Island, Texas  |
+-----------+--------+---------+---------+-----------+----------------+

Number range CHAPTERNumber range CHAPTERTable 2. Selected surface
observations for Tropical Storm Erin, 15-17 August 2007. Observations in
Oklahoma are included for 19 August when Erin was no longer a tropical
cyclone.

+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Location        | M   |     | M   |       |     | St  | St  | To  |
|                 | ini |     | axi |       |     | orm | orm | tal |
|                 | mum |     | mum |       |     | su  |     |     |
|                 | Sea |     | S   |       |     | rge | t   | r   |
|                 | Le  |     | urf |       |     |     | ide | ain |
|                 | vel |     | ace |       |     | (   |     |     |
|                 | Pr  |     |     |       |     | ft) | (   | (   |
|                 | ess |     | W   |       |     | ^c^ | ft) | in) |
|                 | ure |     | ind |       |     |     | ^d^ |     |
|                 |     |     | Sp  |       |     |     |     |     |
|                 |     |     | eed |       |     |     |     |     |
+=================+=====+=====+=====+=======+=====+=====+=====+=====+
|                 | Da  | Pre | Da  | Sust  | G   |     |     |     |
|                 | te/ | ss. | te/ | ained | ust |     |     |     |
|                 |     |     |     |       |     |     |     |     |
|                 | t   | (   | t   | (k    | (   |     |     |     |
|                 | ime | mb) | ime | t)^b^ | kt) |     |     |     |
|                 |     |     |     |       |     |     |     |     |
|                 | (U  |     | (U  |       |     |     |     |     |
|                 | TC) |     | TC) |       |     |     |     |     |
|                 |     |     | ^a^ |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **              |     |     |     |       |     |     |     |     |
| Buoys/C-MAN/NOS |     |     |     |       |     |     |     |     |
| Sites**         |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Buoy 42019 (60  | 1   | 100 | 1   | 27    | 37  |     |     |     |
| n mi S of       | 6/0 | 6.9 | 6/0 |       |     |     |     |     |
| Freeport, TX at | 850 |     | 450 |       |     |     |     |     |
| 27.91°N         |     |     |     |       |     |     |     |     |
| 95.36°W)        |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Port O'Connor   |     |     | 1   | 28    | 34  |     |     |     |
| TCOON (PCNT2)   |     |     | 6/1 |       |     |     |     |     |
|                 |     |     | 000 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Port Aransas    |     |     | u   |       | 40  |     |     | 2   |
| NWR RAWS        |     |     | nkn |       |     |     |     | .81 |
|                 |     |     | own |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
|                 |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Texas**       |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Official**    |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Bush-I          |     |     |     |       |     |     |     | 2   |
| ntercontinental |     |     |     |       |     |     |     | .59 |
| Airport (KIAH)  |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Palacios (KPSX) |     |     |     |       |     |     |     | 3   |
|                 |     |     |     |       |     |     |     | .88 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Pearland (KLVJ) |     |     |     |       |     |     |     | 3   |
|                 |     |     |     |       |     |     |     | .18 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Wharton (KARM)  |     |     |     |       |     |     |     | 2   |
|                 |     |     |     |       |     |     |     | .78 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Unofficial**  |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Jamaica Beach   | 1   | 100 | 1   | 26    | 34  | 3   |     |     |
| (western        | 6/0 | 9.7 | 6/1 |       |     | .10 |     |     |
| Galveston       | 859 |     | 523 |       |     |     |     |     |
| Island)         |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| USCG Freeport   |     |     | 1   | 30    | 35  |     |     |     |
|                 |     |     | 6/2 |       |     |     |     |     |
|                 |     |     | 136 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Hunting Bayou @ |     |     |     |       |     |     |     | 9   |
| Lockwood        |     |     |     |       |     |     |     | .65 |
| (Houston area)  |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| FO1 @ Sens Road |     |     |     |       |     |     |     | 9   |
| (Houston area)  |     |     |     |       |     |     |     | .25 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Little Cedar    |     |     |     |       |     |     |     | 8   |
| Bayou @ 8^th^   |     |     |     |       |     |     |     | .35 |
| St (Houston     |     |     |     |       |     |     |     |     |
| area)           |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Buffalo Bayou @ |     |     |     |       |     |     |     | 7   |
| Turning Basin   |     |     |     |       |     |     |     | .99 |
| (Houston area)  |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Beltway 8 @     |     |     |     |       |     |     |     | 7   |
| I-45 (Houston   |     |     |     |       |     |     |     | .01 |
| area)           |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Beamer Ditch @  |     |     |     |       |     |     |     | 6   |
| Hughes (Houston |     |     |     |       |     |     |     | .02 |
| area)           |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Mary's Creek @  |     |     |     |       |     |     |     | 5   |
| Melodywood      |     |     |     |       |     |     |     | .00 |
| (Houston)       |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Houston Heights |     |     |     |       |     |     |     | 5   |
|                 |     |     |     |       |     |     |     | .02 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Matagorda       |     |     |     |       |     |     |     | 4   |
|                 |     |     |     |       |     |     |     | .14 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Columbus        |     |     |     |       |     |     |     | 3   |
|                 |     |     |     |       |     |     |     | .85 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Wharton         |     |     |     |       |     |     |     | 3   |
|                 |     |     |     |       |     |     |     | .51 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Houston         |     |     |     |       |     |     |     | 3   |
| Westbury        |     |     |     |       |     |     |     | .44 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Alvin           |     |     |     |       |     |     |     | 3   |
|                 |     |     |     |       |     |     |     | .40 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Katy            |     |     |     |       |     |     |     | 3   |
|                 |     |     |     |       |     |     |     | .35 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Aransas         |     |     |     |       |     |     |     | 2   |
| Wildlife Refuge |     |     |     |       |     |     |     | .91 |
| (ARNT2)         |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Victoria        |     |     |     |       |     |     |     | 2   |
| (VICT2)         |     |     |     |       |     |     |     | .81 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Port Lavaca     |     |     |     |       |     |     |     | 3   |
| (PVAT2)         |     |     |     |       |     |     |     | .25 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Matagorda       |     |     |     |       |     |     |     | 4   |
| Island RAWS     |     |     |     |       |     |     |     | .19 |
| (MIRT2)         |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Port O'Connor   |     |     |     |       |     |     |     | 3   |
|                 |     |     |     |       |     |     |     | .26 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
|                 |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Oklahoma**    |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Official**    |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Watonga         |     |     | 1   | 42    | 71  |     |     |     |
| Regional        |     |     | 9/0 |       |     |     |     |     |
| Airport (KJWG)  |     |     | 754 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 7 mi W of       | 1   | 99  | 1   | 47    | 63  |     |     |     |
| Watonga         | 9/0 | 9.1 | 9/0 |       |     |     |     |     |
| (Mesonet WATO)  | 725 |     | 725 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 4 mi NNW of     | 1   | 100 | 1   | 43    | 65  |     |     | 9   |
| Fort Cobb       | 9/0 | 3.9 | 9/0 |       |     |     |     | .30 |
| (Mesonet FTCB)  | 525 |     | 525 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Wiley Post      | 1   | 100 | 1   | 39    | 49  |     |     |     |
| Airport         | 9/1 | 4.2 | 9/0 |       |     |     |     |     |
| (Oklahoma       | 153 |     | 919 |       |     |     |     |     |
| City/Bethany)   |     |     |     |       |     |     |     |     |
| (KPWA)          |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 2 mi NE of      | 1   | 100 | 1   | 38    | 52  |     |     | 5   |
| Kingfisher      | 9/1 | 4.2 | 9/0 |       |     |     |     | .68 |
| (Mesonet KING)  | 140 |     | 925 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Will Rogers     | 1   | 1   | 1   | 38    | 49  |     |     | 5   |
| World Airport,  | 9/1 | 006 | 9/0 |       |     |     |     | .38 |
| Oklahoma City   | 152 |     | 925 |       |     |     |     |     |
| (KOKC)          |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Guthrie-Edmond  | 1   | 100 | 1   | 37    | 48  |     |     |     |
| Regional        | 9/1 | 6.6 | 9/0 |       |     |     |     |     |
| Airport (KGOK)  | 253 |     | 829 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| El Reno         |     |     | 1   | 37    | 48  |     |     |     |
| Regional        |     |     | 9/0 |       |     |     |     |     |
| Airport (KRQO)  |     |     | 741 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 2 mi SSW of     | 1   | 100 | 1   | 37    | 50  |     |     | 6   |
| Minco (Mesonet  | 9/0 | 4.7 | 9/0 |       |     |     |     | .80 |
| MINC)           | 720 |     | 815 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 7 mi W of       | 1   | 100 | 1   | 37    | 56  |     |     |     |
| Hinton (Mesonet | 9/0 | 2.3 | 9/0 |       |     |     |     |     |
| HINT)           | 800 |     | 625 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 5 mi WNW of El  | 1   | 100 | 1   | 37    | 47  |     |     | 8   |
| Reno (Mesonet   | 9/1 | 3.6 | 9/0 |       |     |     |     | .45 |
| ELRE)           | 050 |     | 745 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 3 mi W of       | 1   | 100 | 1   | 36    | 46  |     |     |     |
| Medicine Park   | 9/0 | 2.4 | 9/0 |       |     |     |     |     |
| (Mesonet MEDI)  | 435 |     | 420 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 4 mi WSW of     | 1   | 100 | 1   | 36    | 48  |     |     | 6   |
| Weatherford     | 9/0 | 0.9 | 9/0 |       |     |     |     | .53 |
| (Mesonet WEAT)  | 630 |     | 505 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Norman NWS      |     |     |     |       |     |     |     | 7   |
|                 |     |     |     |       |     |     |     | .67 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 4 mi WNW of     | 1   | 100 | 1   | 27    | 40  |     |     | 6   |
| Rush Springs    | 9/0 | 5.4 | 9/0 |       |     |     |     | .44 |
| (Mesonet ACME)  | 740 |     | 710 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Shawnee         | 1   | 100 | 1   | 27    | 38  |     |     | 5   |
| (Mesonet SHAW)  | 9/1 | 7.7 | 9/1 |       |     |     |     | .14 |
|                 | 335 |     | 220 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Unofficial**  |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 9.8 mi NNW of   |     |     |     |       |     |     |     | 11  |
| Geary           |     |     |     |       |     |     |     | .03 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Watonga         |     |     |     |       |     |     |     | 9   |
|                 |     |     |     |       |     |     |     | .11 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Sedan           |     |     |     |       |     |     |     | 8   |
|                 |     |     |     |       |     |     |     | .84 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 7.9 mi ESE of   |     |     |     |       |     |     |     | 8   |
| Norman          |     |     |     |       |     |     |     | .68 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Walters         |     |     |     |       |     |     |     | 8   |
|                 |     |     |     |       |     |     |     | .50 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Lookeba         |     |     |     |       |     |     |     | 8   |
|                 |     |     |     |       |     |     |     | .15 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Shawnee         |     |     |     |       |     |     |     | 7   |
|                 |     |     |     |       |     |     |     | .11 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Chickasha       |     |     |     |       |     |     |     | 6   |
|                 |     |     |     |       |     |     |     | .18 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 2 mi W of       |     |     |     |       |     |     |     | 5   |
| Lindsay         |     |     |     |       |     |     |     | .12 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+

^a^ Date/time is for sustained wind when both sustained and gust are
listed.

^b^ Except as noted, sustained wind averaging periods for C-MAN and
land-based ASOS reports are 2 min; buoy averaging periods are 8 min;
wind averaging period for Oklahoma Mesonet sites is 5 min.

^c^ Storm surge is water height above normal astronomical tide level.

^d^ Storm tide is water height above National Geodetic Vertical Datum
(1929 mean sea level).

Number range CHAPTERTable 3. Preliminary track forecast evaluation
(heterogeneous sample) for Tropical Storm Erin, 15-17 August 2007.
Forecast errors (n mi) are followed by the number of forecasts in
parentheses. Errors smaller than the NHC official forecast are shown in
bold-face type. Verification includes the depression stage.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Number    | For   |       |       |       |       |       |       |
| range     | ecast |       |       |       |       |       |       |
| CHAPTE    | P     |       |       |       |       |       |       |
| RForecast | eriod |       |       |       |       |       |       |
| Technique | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 55 (  | 112 ( | 182 ( | 323 ( |       |       |       |
|           | 7)    | 6)    | 4)    | 2)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | 69 (  | 123 ( |       |       |       |       |       |
|           | 3)    | 2)    |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | **36  | **66  | 99 (  | 161 ( |       |       |       |
|           | (     | (     | 4)    | 2)    |       |       |       |
|           | 7)**  | 6)**  |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| HWFI      | **38  | **63  | 99 (  | 128 ( |       |       |       |
|           | (     | (     | 4)    | 2)    |       |       |       |
|           | 7)**  | 6)**  |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | 54 (  | 102 ( | 170 ( | 312 ( |       |       |       |
|           | 6)    | 5)    | 3)    | 1)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | 73 (  | 127 ( | 177 ( | 208 ( |       |       |       |
|           | 7)    | 5)    | 4)    | 2)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | 51 (  | 81 (  | 128 ( | 168 ( |       |       |       |
|           | 6)    | 5)    | 3)    | 2)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 43 (  | 76 (  | **94  | **106 |       |       |       |
|           | 7)    | 6)    | (     | (     |       |       |       |
|           |       |       | 4)**  | 2)**  |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | 44 (  | 78 (  | **92  | **95  |       |       |       |
|           | 7)    | 6)    | (     | (     |       |       |       |
|           |       |       | 4)**  | 2)**  |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 49 (  | 85 (  | 103 ( | **106 |       |       |       |
|           | 7)    | 6)    | 4)    | (     |       |       |       |
|           |       |       |       | 2)**  |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | 43 (  | 79 (  | 121 ( | 177 ( |       |       |       |
|           | 7)    | 6)    | 4)    | 2)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | **41  | 70 (  |       |       |       |       |       |
|           | (     | 2)    |       |       |       |       |       |
|           | 3)**  |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | 57 (  | 85 (  | 105 ( |       |       |       |       |
|           | 3)    | 3)    | 1)    |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 42 (  | 70 (  | 97 (  | 110 ( |       |       |       |
|           | 7)    | 6)    | 4)    | 2)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 35    | 61    | 86    | 112   | 162   | 221   | 290   |
| Official  | (     | (     | (     | (     | (     | (885) | (723) |
|           | 1852) | 1686) | 1519) | 1362) | 1100) |       |       |
| (         |       |       |       |       |       |       |       |
| 2002-2006 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Table 4. Preliminary intensity forecast evaluation (heterogeneous
sample) for Tropical Storm Erin, 15-17 August 2007. Forecast errors (kt)
are followed by the number of forecasts in parentheses. Errors smaller
than the NHC official forecast are shown in bold-face type. Verification
includes the depression stage.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Number    | For   |       |       |       |       |       |       |
| range     | ecast |       |       |       |       |       |       |
| CHAPTE    | P     |       |       |       |       |       |       |
| RForecast | eriod |       |       |       |       |       |       |
| Technique | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| SHF5      | 7.9 ( | 14.3  | 22.8  | 23.5  |       |       |       |
|           | 7)    | ( 6)  | ( 4)  | ( 2)  |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GHMI      | **4.3 | **3.2 | **1.8 | **1.5 |       |       |       |
|           | (     | (     | (     | (     |       |       |       |
|           | 7)**  | 6)**  | 4)**  | 2)**  |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| HWFI      | **5.3 | 6.5 ( | **3.5 | 6.5 ( |       |       |       |
|           | (     | 6)    | (     | 2)    |       |       |       |
|           | 7)**  |       | 4)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| SHIP      | 8.1 ( | 13.3  | 20.8  | 24.5  |       |       |       |
|           | 7)    | ( 6)  | ( 4)  | ( 2)  |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| DSHP      | 6.7 ( | 5.7 ( | **6.3 | 4.5 ( |       |       |       |
|           | 7)    | 6)    | (     | 2)    |       |       |       |
|           |       |       | 4)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | 6.7 ( | 8.0 ( | **2.0 |       |       |       |       |
|           | 3)    | 3)    | (     |       |       |       |       |
|           |       |       | 1)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| ICON      | **4.1 | **3.7 | **2.5 | **1.0 |       |       |       |
|           | (     | (     | (     | (     |       |       |       |
|           | 7)**  | 6)**  | 4)**  | 2)**  |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 5.7 ( | 5.0 ( | 7.5 ( | 2.5 ( |       |       |       |
|           | 7)    | 6)    | 4)    | 2)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 6.4   | 9.8   | 12.0  | 14.1  | 18.3  | 19.8  | 21.8  |
| Official  |       |       |       |       |       |       |       |
|           | \(1   | \(1   | \(1   | \(1   | \(1   | \(    | \(    |
| (         | 852\) | 686\) | 519\) | 362\) | 100\) | 885\) | 723\) |
| 2002-2006 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Number range CHAPTERTable 5. Coastal watch and warning summary for
Tropical Storm Erin, 15-17 August 2007.

  ----------------------- ----------------------- -----------------------
  Date/Time (UTC)         Action                  Location

  15 / 0300               Tropical Storm Watch    Brownsville to Freeport
                          issued                  

  15 / 0300               Tropical Storm Watch    Rio San Fernando to
                          issued                  Texas/Mexico Border

  15 / 1500               Tropical Storm Watch    Brownsville to Freeport
                          changed to Tropical     
                          Storm Warning           

  15 / 2100               Tropical Storm Watch    All
                          discontinued            

  15 / 2100               Tropical Storm Warning  Brownsville to San Luis
                          modified to             Pass

  16 / 0900               Tropical Storm Warning  Port Mansfield to San
                          modified to             Luis Pass

  16 / 1200               Tropical Storm Warning  All
                          discontinued            
  ----------------------- ----------------------- -----------------------

![](media/image1.wmf){width="7.747222222222222in"
height="6.036111111111111in"}

Number range CHAPTERFigure 1. Best track positions for Tropical Storm
Erin, 15-17 August 2007.

![](media/image2.wmf){width="7.501388888888889in"
height="5.147916666666666in"}

Number range CHAPTERFigure 2. Selected wind observations and best track
maximum sustained surface wind speed curve for Tropical Storm Erin,
15-17 August 2007. Solid vertical line indicates time of landfall of the
center on the Texas coast. Aircraft observations have been adjusted for
elevation using 90%, 80%, and 80% reduction factors for observations
from 700 mb, 850 mb, and 1500 ft, respectively.

![](media/image3.png){width="7.872916666666667in"
height="5.405555555555556in"}

Number range CHAPTERFigure 3. Selected pressure observations and best
track minimum central pressure curve for Tropical Storm Erin, 15-17
August 2007. Solid vertical line indicates time of landfall of the
center on the Texas coast.

![](media/image4.jpeg){width="7.120138888888889in"
height="5.841666666666667in"}

Figure 4. WSR-88D radar reflectivity image over Oklahoma at 1200 UTC 19
August 2007. Graphic courtesy of the National Weather Service Forecast
Office in Norman, Oklahoma.

![](media/image5.png){width="7.666666666666667in" height="5.5625in"}

Figure 5. Storm-total rainfall accumulations (inches) from Tropical
Storm Erin and its remnantsNumber range CHAPTER. Graphic courtesy of the
Hydrometeorological Prediction Center.

[^1]: A tropical cyclone is defined by NHC as "a warm-core, non-frontal,
    synoptic-scale cyclone, originating over tropical or subtropical
    waters, with organized deep convection and a closed surface wind
    circulation about a well-defined center."

[^2]: An extratropical cyclone is defined by NHC as "a synoptic-scale
    low pressure system whose primary energy source is baroclinic."

[^3]: A subtropical cyclone is defined by NHC as "a non-frontal low
    pressure system that has characteristics of both tropical and
    extratropical cyclones."