Session No. 10

# Course Title: Hazard Mapping and Modeling

**Session 10: Hurricane Storm Surge Modeling and Analysis**

**Prepared by John C. Pine, Director, Disaster Science and Management,
LSU**

**Hassan Mashriqui, Assistant Professor Research, LSU Hurricane Center,
LSU**

## Time: 3 hrs

**Objectives:**

**10.1 Describe the characteristics of a hurricane and the hazards
associated with a hurricane storm surge.**

**10.2 Understand the nature and uses of the Saffir-Simpson Hurricane
Scale**

**10.3 Understand the uses, capabilities, limitations and outputs of the
SLOSH Storm Surge Modeling Program**

**Overall Goal: This course is to contribute to the reduction of the
growing toll (deaths and injuries, property loss, environmental
degradation, etc.) of disasters in the United States by providing an
understanding of the significant role of mapping and modeling in the
management of hazards.**

**Session Goal: Students in this session will understand the nature of
storm surge hazards and methods of modeling this hazard to reduce the
adverse impacts of storm surge hazards.**

**Scope:**

This session provides an introduction to the characteristics of
hurricanes and the hazards associated with hurricane storm surge.
Modeling hurricane storm surge using the National Weather Service (NWS)
SLOSH (Sea, Lake, and Overland Surges from Hurricanes) model will be
examined to identify the type of information needed to characterize the
nature and impacts of hurricane storm surge. The limitations of
hurricane storm surge modeling will be discussed and how to read output
maps and displays from the SLOSH. Finally, the session will examine the
purpose and limitations for the NWS SLOSH hurricane storm surge software
and how it is used for planning and emergency response operations.

Readings:

*Student Reading:*

Cutter, Susan L., Jerry T. Mitchell & Michael S. Scott (2000). Revealing
the Vulnerability of People and Places: A Case Study of Georgetown
County, South Carolina. *Annals of the Association of American
Geographers*. Volume 90 Issue 4. Page 713.  

## Houston, Samuel H., Wilson Shaffer, Mark Powell, Jye Chen. (1999). Comparisons of HRD and SLOSH Surface Wind Fields in Hurricanes: Implications for Storm Surge Modeling

*Weather and Forecasting:* Vol. 14, No. 5, pp. 671--686.

Mercado, Aurelio (1994). On the use of NOAA\'s storm surge model, SLOSH,
in managing coastal hazards - the experience in Puerto Rico. *Natural
Hazards.* Vol. 10 \# 3 pp. 235-246.

Natural Disaster Survey Report Hurricane Andrew September 23 - 26, 1992
(1993). U.S. Department of Commerce, NOAA. Silver Spring, MD.

*SLOSH Display Training* (2003). "Introduction," Pages 4 -- 19 and
"SLOSH Display Program pp. 29 -- 43.FEMA, RUS and the U.S. Army Corps of
Engineers.

*Additional Instructor Reading:*

[Blain, C. A.](http://adsabs.harvard.edu/cgi-bin/author_form?author=Blain,+C&fullauthor=Blain, C. A.&charset=ISO-8859-1&db_key=PHY);
[Westerink, J. J.](http://adsabs.harvard.edu/cgi-bin/author_form?author=Westerink,+J&fullauthor=Westerink, J. J.&charset=ISO-8859-1&db_key=PHY);
[Luettich, R. A.](http://adsabs.harvard.edu/cgi-bin/author_form?author=Luettich,+R&fullauthor=Luettich, R. A.&charset=ISO-8859-1&db_key=PHY)
(1994). The influence of domain size on the response characteristics of
a hurricane storm surge model. Journal of Geophysical Research, Volume
99, Issue C9, p. 18467-18480.

Mark D.
Powell[\*](http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V3M-3WSCXTY-5&_coverDate=09%2F01%2F1998&_alid=447548286&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=5734&_sort=d&view=c&_acct=C000061383&_version=1&_urlVersion=0&_userid=3787556&md5=295a3c544a4d72526229dd64c401ae67#cor*%23cor*),
Sam H. Houston, Luis R. Amat and Nirva Morisseau-Leroy (1998). The HRD
real-time hurricane wind analysis system. [*Journal of Wind Engineering
and Industrial
Aerodynamics.*](http://www.sciencedirect.com/science?_ob=PublicationURL&_cdi=5734&_pubType=J&_auth=y&_acct=C000061383&_version=1&_urlVersion=0&_userid=3787556&md5=f21e4a7d347b0a5b79e5fe82bb3c43b3)
[Volumes
77-78](http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235734%231998%23999219999%23104529%23FLA%23&_cdi=5734&_pubType=J&view=c&_auth=y&_acct=C000061383&_version=1&_urlVersion=0&_userid=3787556&md5=e0f7a318c476ae494038de338df82b35)
, 1 September 1998, Pages 53-64.

Organization of American States (1991). *Primer on Natural Hazard
Management in Integrated Regional Development Planning.* Washington,
D.C.

**General Requirements:**

Power point slides are provided for the instructor's use, if so desired.

The Natural Disaster Survey Reports from Hurricane Andrew is provided as
readings as a part of this class. Additional Storm Reports are included
in the course materials as an alternative for to students interested in
other storms impacting the United States. In addition, several Handouts
concerning technical background on hurricane storm characteristics are
included with this session as a resource for students. The instructor
may encourage students to review the session handouts prior to the
session so as to provide additional information on the nature of
tropical cyclones and their impacts on the built environment.

Objective 10.1 -- Define the characteristics of a hurricane and the
hazards associated with a hurricane storm surge.

Requirements:

A Natural Disaster Survey Report for Hurricane Andrew was prepared by
the National Oceanic and Atmospheric Administration (NOAA) and provided
for the class as an illustration of the nature and impact of a tropical
cyclone. Alternative storm reports are available for class use as an
alternative to Hurricane Andrew. Encourage students to read the
Hurricane Andrew Storm Report as background on this natural hazard.
Additional Survey Reports are included with this session so as to give
students additional hurricanes to analyze.

**NOTE:** Appencix C provides definitions for measurement terms used in
storm surge modeling.

**Remarks:**

**I. The Hurricane Environment**

A.  A **hurricane** is a **tropical cyclone.** These storms occur in the
    Northern Hemisphere originating over warm tropical waters with
    sustained winds of at least 74 mph (64 knots) or greater for a
    duration of six to eight hours (see Slide 3).

B.  Areas in the United States vulnerable to hurricanes include the
    Atlantic and Gulf coasts from Texas to Maine, the territories in the
    Caribbean, and tropical areas of the western Pacific, including
    Hawaii, Guam, American Samoa, and Saipan. Hurricanes are seasonal in
    nature. [Handout #1 Session 10]{.underline} provides a list of the
    more powerful Tropical Cyclones impacting the United States in
    recent years. It also explains the seasonal nature of these hazards
    by geographic area (see Slide 4).

C. **Tropical cyclone hazard impacts**

> 1\. Strong Winds cause most of the structural damage

2\. Heavy rainfall creates flooding

> 3\. Storm surge causes most deaths
>
> 4\. Storm surge causes much salt contamination of agricultural land
> (see Slide 5) (Smith 2001, p. 218).
>
> D. Tropical cyclones are classified from tropical depressions to
> hurricanes. Refer to [Handout #4 Session 10]{.underline} for
> additional information.
>
> E. **Natural phenomena, which affect a hurricane include:** (*See
> [Handout #2 Session 10]{.underline} for additional information on the
> factors that affect the development and intensity of a tropical
> cyclone).*
>
> 1\. Temperature of the water,
>
> 2\. The Gulf Stream, and
>
> 3\. Steering wind currents.
>
> a\. An example would include trade winds. Trade winds are the wind
> system, occupying most of the tropics, which are northeasterly in the
> Northern Hemisphere and southeasterly in the Southern Hemisphere. The
> speed and force of the wind is measured by an **anemometer.**.
>
> *See [Handout #3 Session 10]{.underline} for additional background
> information on Hurricane Storm Dynamics*

**Question:** Describe the characteristics of Hurricane Andrew (peak
winds, path, approximate size of the storm, and approximate size of the
landfall area directly impacted by the storm, and geographic area
impacted. (See the following student reading in the course materials for
this session. Rappaport, Ed (1993). *Hurricane Andrew: August 16 -- 28,
1992.* Preliminary Report. National Hurricane Center and Natural
Disaster Survey Report Hurricane Andrew September 23 - 26, 1992 (1993).
U.S. Department of Commerce, NOAA. Silver Spring, MD.)

**III. Hurricane Storm Surge Hazard**

**Question:** Hurricane Andrew was a powerful Category 5 storm striking
Florida and causing extensive damage. What influenced the nature of the
storm surge? The Hurricane Andrew Report describes the nature of the
storm and what factors influenced this powerful storm. (See Rappaport,
Ed (1993). *Hurricane Andrew: August 16 -- 28, 1992.* Preliminary
Report. National Hurricane Center and Natural Disaster Survey Report
Hurricane Andrew September 23 - 26, 1992 (1993). U.S. Department of
Commerce, NOAA. Silver Spring, MD. Ask the class to review the Hurricane
Andrew Report and identify the following meteorological parameters:

> • Intensity of the storm as measured by the central barometric
> pressure and Maximum surface winds.

• Atmospheric Pressure

• Track of the storm

• Forward speed of the storm

• Radium of maximum winds

> A. The **elevation of the storm surge** within a coastal basin depends
> upon: the **meteorological parameters** of the hurricane and the
> **physical characteristics** existing within the basin. Storm surge
> models such as SLOSH take these parameters into consideration in
> determining the nature of a storm surge for a specific storm.
>
> 1\. The **meteorological parameters** affecting the amount of storm
> surge generated include (see Slide 5):
>
> a\. The **intensity** of the hurricane is measured by the central
> barometric pressure and maximum surface winds at the center of the
> storm. Storm surge begins to build while the hurricane is still far
> out at sea over deep water. The low pressure near the center of the
> storm causes the water to rise. In deep water, a counter current
> develops well below the surface, which counters an attempt by the wind
> to build up surges.
>
> b\. **Atmospheric Pressure** is exerted by the atmosphere at a given
> point. Its measurement can be expressed in several ways. One is in
> millibars. Another is in inches or millimeters of mercury (Hg). Also
> known as barometric pressure.
>
> c\. Path or forward **track of the storm**,
>
> d\. **Forward speed**, and
>
> e\. **Radius of maximum winds** (storm size). The radius of maximum
> winds is measured from the center of the hurricane to the location of
> the highest wind speeds within the storm. This distance can vary from
> as little as 4 miles to as much a 50 miles. Due to the
> counter-clockwise rotation of the wind field, the highest surge levels
> are generally located at the right of the forward track of the
> hurricane (see Slide 6).
>
> *Each tropical cyclone is unique. The above elements have a critical
> impact on the nature of the storm, its path and its impact on the
> built environment. The detailed reports from the National Weather
> Service explain the specific meteorological parameters of a hurricane.
> Refer the class to the NWS Hurricane Reports that are included with
> this session for a closer examination of the meteorological parameters
> of the storm.*
>
> 2\. The **physical characteristics of a basin** also influence
> potential surge heights. The SLOSH model which is discussed in greater
> detail later in this session, examines the hurricane hazard by
> geographic basin. These factors are inputs in the model.
>
> a\. The level of surge in a particular area is greatly influenced by
> the slope of the continental shelf or the **basin bathymetry**. A
> shallow slope off the coast shown in the Figure below **will allow a
> greater surge to inundate coastal communities**.
>
> 1\) Communities with a steeper continental shelf **will not see as
> much surge inundation** (see Slide 7).
>
> 2\) As the water depth decreases closer to the shore, the excess water
> that is built up by the storm is not able to dissipate. The increased
> water has no place to go except up onto the shore.
>
> 3)The surface current also induces **currents in subsurface water**.
> The surface currents are impacted by the depth of the water and by the
> intensity and forward motion of the hurricane. For example, a fast
> moving hurricane of moderate intensity may only induce currents to a
> depth of a hundred feet, whereas a slow moving hurricane of moderate
> intensity might induce currents to several hundred feet.
>
> 4\) Waves are directly affected by water depth and will break and
> dissipate their energy in **shallow water**. A steep continental shelf
> will allow large ocean waves to approach the coastline before breaking
> thus increasing wave setup. This phenomenon is primarily a concern
> near the coastline because large wave are generally not transmitted
> inland.
>
> 5\) Horizontal coastal currents also are impeded by a **sloping
> continental-shelf** and could cause be particularly conducive to the
> formation of large storm surges in a gradual sloping continental
> shelf.
>
> 6\) Waves and swells breaking at or near the coast also transport
> water shoreward. During storms when there is an increase in wave
> height and **wave steepness**, water cannot flow back to the sea as
> rapidly as it is brought shoreward. This results in a phenomenon known
> as "**wave setup**" and causes a further increase of water level along
> the coastline.
>
> b\. **Roughness** of the continental shelf,
>
> c\. **Configuration** of the coastline, and
>
> d\. The existence of significant **natural or man made barriers.**
>
> e\. In addition to the physical characteristics of the basin, another
> factor which affects the storm surge heights is the initial water
> level within the basin at the time of arrival of a hurricane. The
> water level could be either a normal high or low tide. The tide level
> when a hurricane

*See Handout \# 4 Session for additional background information on Storm
Surge-Structure Interaction. Hurricane Andrew's impact on the built
environment was directly related to the characteristics of the storm as
well as the basin.*

**IV. Storm Uncertainty and anticipating stronger storms**

> A. Hurricanes present two problems to the emergency management
> community. First there is always the uncertainty about how **intense**
> the storm will be when it finally makes landfall. Emergency managers
> and local officials balance that uncertainty with the human and
> economic risks to their community. This is why a rule of thumb for
> emergency managers is to plan for a storm one category higher than
> what is forecasted. This is a reasonable precaution to help minimize
> the loss of life from hurricanes (see Slide 8).
>
> B. The second uncertainty is associated with the hurricane storm
> track. The path and direction of the storm can change at any point
> making the actual area impacted by the storm as it makes landfall
> difficult to predict. A review of past hurricanes illustrates the
> difficulty in precisely predicting the actual impact area for the
> landfall of the storm and its intensity.

Objective 10.2 - Explain the Saffir-Simpson Hurricane Scale

**Requirements:**

Students will be asked to apply the Saffir-Simpson Scale to Hurricane
Andrew.

**Remarks**

I. The **Saffir-Simpson Damage Potential Scale** (see Slide 9) provides
a means of quantifying the potential storm surge generated by a
hurricane. It was developed in the early 1970s by Herbert Saffir a
consulting engineer, and Robert Simpson, then Director of the National
Hurricane Center, to measure the intensity of a hurricane. Handout #5
Session 10 provides a summary of the Saffir Simpson Damage Potential
Scale.

> A. It is a descriptive scale that categorizes a storm and its
> potential damage based on a storm's barometric pressure, wind speeds,
> and storm surge. The scale provides a range of wind speeds and normal
> surge heights associated with each of the five categories of
> hurricanes.
>
> B. Scale numbers are available to public safety officials when a
> hurricane is within 72 hours of landfall.

C. Scale assessments are revised regularly as new observations are made.

> D. The Saffir Simpsn Hurricane Scale was intended for use as a general
> guide by public safety officials during hurricane emergencies. It does
> not reflect the effects of varying localized bathymetry, coastline
> configuration, barriers, or other factors that could influence the
> surge heights that occur at differing locations during a single
> hurricane event.
>
> E. Public safety organizations are kept informed of new estimates of
> the hurricane\'s disaster potential. In practice, sustained surface
> wind speed (1-minute average) is the parameter that determines the
> category since storm surge is strongly dependent on the slope of the
> continental shelf (National Hurricane Center).

II\. Hurricane **Watches and Warnings**

> A hurricane watch is issued when there is a threat of hurricane
> conditions within 24-36 hours. A hurricane warning is issued when
> hurricane conditions (winds of 74 miles per hour or greater, or
> dangerously high water and rough seas) are expected in 24 hours or
> less.

**Question:** Using the Saffir-Simpson Damage Potential Scale identify
and justify the classification of Hurricane Andrew. Identify and justify
the classification of the hurricane for each of the hurricanes assigned
to the groups in the class.

Objective 10.3. Clarify the uses, capabilities, limitations and outputs
of the SLOSH Hurricane Storm Surge Model

Requirements:

A PowerPoint presentation is provided for the discussion of the SLOSH
Storm Surge Model.

A copy of the SLOSH Display Training Manual along with a program to
display SLOSH Model outputs from U.S. applications of the model. The
SLOSH Model display program is provided as an option for use in the
class or by students who wish to examine SLOSH model outputs for their
region.

**Remarks:**

I. The **National Hurricane Center** (NHC) in Miami, Florida (National
Weather Service) tracks tropical cyclones from the tropical depression
stage through the hurricane stage over the North Atlantic Ocean,
Caribbean Sea, Gulf of Mexico and Eastern Pacific Ocean. NHC forecasts
the future position and intensity of the cyclones using mathematical
computer models.

**Question:** What is the mission of the National Hurricane Center? How
does the SLOSH Model fit within the NHC's responsibilities and
organizational mission?

> *The NHC's mission is to save lives, mitigate property loss, and
> improve economic efficiency by issuing the best watches, warnings,
> forecasts and analyses of hazardous tropical weather, and by
> increasing understanding of these hazards. The TPC vision is to be
> America\'s calm, clear and trusted voice in the eye of the storm and,
> with its partners, enable communities to be safe from tropical weather
> threats. Modeling of hurricanes is critical in supporting federal,
> state and local efforts for the development of emergency response
> plans to hurricanes and in emergency operations to a specific storm.*
>
> *The NHC collaborates with universities, government research
> laboratories, international tropical weather centers, the private
> sector and other National Weather Service components to maintain its
> leading edge in tropical meteorology through coordinated operations,
> research, training and forecast development techniques.*

II\. The **SLOSH Model** (Sea, Lake, and Overland Surges from
Hurricanes) is one of the sophisticated mathematical models used by NHC
to calculate potential surge heights from hurricanes for storm surge
warnings and hurricane evacuation studies all over the eastern seaboard
of the U.S.

> A. The SLOSH model is a critical tool in accomplishing the NHC
> mission. SLOSH is used to support **NWS hurricane warnings and
> regional evacuation plans**. SLOSH was developed by Chester P.
> Jelesnianski and Jye Chen of the National Weather Service in 1978.
>
> B. The SLOSH model is used to represent a tropical cyclone and to
> forecast the future motion and intensity of a cyclone. NHC forecasters
> interpret model results to arrive at a final track and intensity
> forecast, distributing it to the public in the form of advisories (see
> Slide 10).
>
> 1\. The SLOSH model **simulates inland flooding** from storm surge and
> permits the overtopping of barriers and flow through barrier gaps. The
> results from SLOSH cane be used in a hazards analysis and help
> estimate the extent and timing of an evacuation (see Slide 11)
> (Allenstein 1985).
>
> 2\. SLOSH analysis can help the decision-maker in a crisis situation
> answer the following questions (see Slide 12) (Allenstein 1985):

a\. What is the nature of the approaching natural threat?

b\. Who is at risk and to what extent?

c\. Where should these people go for safety?

> d\. How much time is there to evacuate?
>
> C. The **model output** contains information concerning the range of
> expected **peak surge heights** within the hurricane warning area
> (basin) (Jarvinen 1985; Mercado 1994).
>
> D. **SLOSH is not a prediction model.** Prediction models step forward
> in time from a set of initial conditions (Allenstein 1985). SLOSH
> requires time varying hurricane forces be provided as boundary
> conditions.
>
> 1\. Boundary conditions are provided through a separate NWS
> atmospheric model (see Slide 13). The conditions include:
>
> a\. **hurricane track**,
>
> b\. **central sea level** **pressure,** and
>
> c\. **radius of maximum wind** into a distribution of sea surface wind
> stress and pressure forces.
>
> 2\. These conditions are combined with basin characteristics to
> generate the abnormal storm surge water levels.
>
> E. The mathematical models used at NHC are of three basic types:
> Statistical, Dynamical or Combination (Statistical and Dynamical
> together) (see Slide 14).
>
> 1\. **Statistical models** forecast the future by using current
> information about the hurricane and comparing it to historical
> knowledge about the behavior of similar tropical cyclones. The
> historical record for storms over the north Atlantic begins in 1871,
> while the record for storms for the east Pacific extends back to 1945.
> Statistical models rely on what has happened such as the climatology
> of past storms.
>
> 2\. **Dynamical models** work differently. They are designed to use
> the results of global atmospheric model forecasts in different ways to
> forecast tropical cyclone motion and intensity. Global models take
> current wind, temperature, pressure and humidity observations and make
> forecasts of the actual atmosphere in which the cyclone exists.
>
> 3\. **Combination models** such as SLOSH use both dynamical and
> statistical approaches to capitalize on the strengths of each. Because
> of their simplicity, statistical models were designed first for
> tropical cyclone forecasting in the late 1960\'s. In the early
> seventies, combination models were developed as global models began
> making forecasts in tropical regions. As computers have become more
> powerful, global models have improved and pure dynamic models are
> beginning to dominate the accuracy race.
>
> 4\. It should be noted that a model is a representation of a complex
> set of elements. It is thus a guide to understanding a hazard and its
> impacts and not a perfect prediction.

**III.** **Uses of SLOSH**

> A. SLOSH was developed for **real time forecasting** of surges from
> hurricanes within selected Gulf and Atlantic coastal basins and for
> evacuation planning (see Slide 15).
>
> 1\. It furnishes **surge heights for open coast**, **bays, estuaries,
> coastal river basins** as well as over inland locations.
>
> 2\. Significant natural and man-made barriers are represented in the
> model and their effects taken into consideration in the calculations
> of surge heights within a basin.
>
> B. SLOSH is used to define flood-prone areas for **evacuation
> planning**. It is a tool in preparing an evacuation plan for coastal
> communities. Regional evacuation studies utilize SLOSH.
>
> 1\. The flood areas in regional evacuation studies are determined by
> compositing peak model surge values from **200 to 300 hypothetical
> hurricanes**. Separate composite flood maps are produced for each of
> the five levels of hurricane intensity.
>
> 2\. SLOSH is also able to estimate the overland tidal surge heights
> and winds that result from **hypothetical hurricanes.** The resultant
> **tidal surge** is then applied to a **specific locale\'s shoreline**,
> incorporating the unique bay and river configurations, water depths,
> bridges, roads and other features (Jelesnianski and Taylor 1973).
>
> C. SLOSH is also designed for use in an **operational mode**; that is,
> for forecast or hind-cast runs. The SLOSH model contains a storm model
> into which simple, time-dependent meteorological data are input and
> from which the driving forces of a simulated storm are calculated.
>
> D. If a local jurisdiction has a Hurricane Evacuation Study (which
> combines SLOSH model results with traffic flow information), the
> jurisdiction does not need information about storm surge heights in a
> real hurricane situation. Local officials only need to know the
> forecast of the storm\'s intensity at landfall and the tide at that
> time to be able to make an appropriate evacuation decision (see Slide
> 16).

**IV. Data requirements** for SLOSH include (see Slide 17).

A. **Storm positions** (Latitude and Longitude) at six-hour intervals
for a 72-hour track.

> B. The lowest atmospheric sea level **pressure** in the eye of the
> hurricane at six-hour intervals.
>
> C. The **storm size** measured from the center to the region of
> maximum winds; commonly referred to as the "radius of maximum winds."
>
> D. The **initial height of the water surface** (well before the storm
> directly affects the area of interest). This initial height is the
> observed still water level occurring about two days before storm
> arrival and includes an existing anomalous rise in the water surface.
>
> 1\. **Tidal fluctuations** immediately prior to landfall have not been
> accounted for because a small error in predicting the phasing of storm
> track and astronomical tide would likely invalidate the model results.
>
> E. The **characteristics of a particular basin** including:

1\. The **topography** of inland areas;

2\. **River basins and waterways**;

3\. **Bathymetry** of near shore areas, bays and large inland water
bodies;

> 4\. Significant natural and man-made **barriers** such as barrier
> islands, dunes, roadbeds, floodwalls, levees, etc.; and
>
> 5\. The nature of the continental shelf.

**V. SLOSH Model Outputs**

> A. SLOSH produces a **Grid** representing a natural basin or large
> geographical area. The smallest grids usually represent an area of
> about 0.01 square miles (see Slide 18). This permits inclusion of
> topographic details such as highway and railroad embankments,
> causeways, levees, etc.

**Question:** Ask students to determine how local officials would use
the SLOSH GRID output? What type of decision would this output support?

> *The SLOSH model provides four major types of information on the
> effects of the simulated hurricanes in an operational mode.*
>
> *1. Surface envelope of the highest surges above mean sea level. The
> surge elevation is determined for each grid cell. The surge height is
> compared to the ground surface elevation which is the average of the
> ground surface elevations found in that grid (see Slide 19).*
>
> *2. Time histories of surges at selected grid points;*
>
> *3. Computed wind speeds at selected grid points;*
>
> *4. Computed wind directions at selected grid points.*
>
> *In addition to the graphic display of model results, SLOSH model
> output for a modeled storm consists of a **tabulated storm history**
> containing hourly values of storm position, speed, direction of
> motion, pressure, and radius of maximum winds; a surface envelope of
> highest surges; and for pre-selected grid points, time-history
> tabulations of values for surge heights, wind speeds, and wind
> directions. If desired, the model can also furnish two-dimensional
> snapshot displays of surges at specified times during a simulation.*
>
> *For decisions made in a planning mode, the major output of the model
> is a vulnerability analysis to identify the areas, populations, and
> facilities which are potentially vulnerable to flooding associated
> with hurricanes. The storm surge data provided by SLOSH is used:*
>
> *1. To develop inundation maps;*
>
> *2. To determine evacuation zones and evacuation scenarios for local
> areas;*
>
> *3. To quantify the population at risk under a range of hurricane
> intensities; and*
>
> *4. To identify major medical institutional and other facilities that
> are potentially vulnerable to storm surge.*
>
> *Graphical output from the SLOSH model displays color-coded storm
> surge heights for a particular area in feet.*

.

> *The storm surge height calculations are applied to a specific
> locale\'s shoreline, incorporating the unique bay and river
> configurations, water depths, bridges, roads and other physical
> features. If the model is being used to estimate storm surge for an
> actual hurricane (as opposed to a hypothetical one), forecast data is
> put in the model every 6 hours and updated as new forecasts become
> available.*
>
> *The time-history data of surge heights, wind speeds, and wind
> directions are tabulated for each pre-selected grid point in the
> model. These data are listed for each grid point at ten-minute
> intervals for a 72-hour segment of a simulated storm track, starting
> 48 hours prior to landfall and continuing for 24 hours after landfall
> or closest approach.*

**VI.** **Potential peak surges for a regional hurricane study**

*One of the most useful outputs from the SLOSH Model are GRID files
representing multiple model runs for a hurricane evacuation study. The
Maximum Envelope of Water "MEOW" represents multiple SLOSH runs. It is
one of the most useful tools for evacuation planning and land use
planning by local government officials.*

> A. The MEOW output may be used in a hazards analysis to determine
> potential **peak surges** in a coastal area. These peak surges or the
> highest surge reached at all locations within an area are included in
> the model application. The highest surge is called the **maximum
> envelope of water** (MEOW) (see Slide 20).
>
> B. The **Maximum Envelopes of Water (MEOWs**) are developed from many
> **peak surges** calculated for individual hurricanes that differ only
> in the point of landfall. Multiple storms are modeled for a study area
> because it is not possible to precisely forecast the ultimate landfall
> location, forward speed, approach direction, and other characteristics
> of a threatening hurricane (see Slide 21).
>
> C. The displays from the MEOW's in a hurricane study **do not predict
> the limits of inundation from a single storm,** but rather delineate
> the areas that are threatened by storm surge **from all hurricane
> scenarios modeled in the study**.
>
> D. The maximum surge calculations (MEOW) determined in a hurricane
> study along a coastline **do not necessarily occur at the same time**.
> The time of the maximum surge for one location may differ by several
> hours from the maximum surge that occurs at another location. A plot
> of the maximum water surface elevation attained at each grid cell over
> the duration of the simulated storm does not represent a "snapshot" of
> the storm surge at a given instant of time. Instead, it represents the
> highest water level at each grid cell during a hurricane irrespective
> of the actual time of occurrence.

**Question:** Ask the class to explain the difference between the MEOW
and the output from a single SLOSH model run.

> *For a single storm, SLOSH represents only the characteristics of one
> storm. The MEOW represents the model outputs from many storms. The
> GRID file from a MEOW, thus represents the highest storm surge for a
> study area from many storms rather than a single one. Local officials
> can use the MEOW to identify potential evacuation routes and
> shelters.*
>
> E. Each MEOW represents the highest maximum surge in a study area
> (**peak surge**). The location of the peak surge depends on:
>
> 1\. Where the eye of a hurricane crosses the coastline,
>
> 2\. Hurricane intensity,
>
> 3\. The bathymetry of the basin,
>
> 4\. Configuration of the line,
>
> 5\. The approach direction of the storm, and
>
> 6\. The radius of maximum winds.
>
> F. There are only 5 MEOW's per basin, one per storm category.

***An Example of the Application of SLOSH:** In the Southeast Louisiana
Hurricane Preparedness Study (Corps 1994), a total of 1,640 simulated
hurricanes (164 storm tracks) were modeled using the SLOSH model. The
characteristics of the simulated hurricanes were determined from an
analysis of historical hurricanes which occurred within the study area.
These tracks had combinations of parameters representing five categories
of hurricane intensity, as described by the Saffir-Simpson Hurricane
Scale; nine approaches directions for landfall (west, west-northwest,
northwest, north northwest, north, north northeast, northeast, east
northeast, and east), two forward speeds of 5 and 15 miles per hour; and
numerous landfall or closest approach locations separated by 20 miles or
less along the coastline. For the Southeast Louisiana Hurricane
Evacuation study prepared by the Corps of Engineers (1994), the SLOSH
Model formed the basis of the study.*

**VII. SLOSH Model Accuracy** (see Slide 22)

> A. The SLOSH model is generally accurate within plus or minus 20
> percent. For example, if the model calculates a peak 10 foot storm
> surge for the event, you can expect the observed peak to range from 8
> to 12 feet.
>
> 1\. An analysis of hurricane forecasts made by the National Hurricane
> Center indicates the magnitude of error that can be expected in
> forecasting the track of approaching hurricanes. The average error in
> the official hurricane track forecast between 1970 and 1079 was 51
> miles for the 12-hour forecast, 109 miles for the 24-hour forecast,
> 247 miles for the 48-hour forecast, and 377 miles for the 72-hour
> forecast (Jarvinen 1985).
>
> 2\. The error range from a study reported in 1985 notes that the error
> range is from --2.16 meters to + 2.68 meters. The mean absolute error
> is 0.43 meters with a standard deviation of 0.61 meters. Seventy-nine
> percent of the errors are within one standard deviation of the mean
> error; 97 percent are within two standard deviations; and 99 percent
> are within three standard deviations (Jarvinen 1985).
>
> 3\. Thus if a storm were forecast to make landfall due south of New
> Orleans in 24 hours, and if, in fact, it made landfall anywhere
> between Dauphin Island, Alabama and Marsh Island, Louisiana, the error
> in the forecast landfall position would be no worse than average.
>
> 4\. There has been a small, but statistically significant, longer
> downward trend in the forecast errors in the Atlantic basin over the
> period 1970-1991. The downward trend is found not only in the 24-hour
> forecast, but also in the 48- and 72- hour forecasts.
>
> B. Errors also occur in forecasting the maximum sustained wind-speed
> of an approaching hurricane. During the period 1970-1979, the average
> error in the official 24-hour wind speed forecast was 15 miles per
> hour (mph), and the average error in the official 24-hour wind speed
> forecast was 15 mph, and the average in the 12 hour forecast was 10
> mph.
>
> C. Hurricane evacuation decision makers should note that an increase
> in wind speed of 10 to 15 mph can easily raise the intensity category
> of the approaching hurricane on category on the Saffir/Simpson
> Hurricane Scale.
>
> D. To account for inaccuracies in forecasting the behavior of
> approaching hurricanes, the National Hurricane Center recommends that
> public officials faced with an eminent evacuation prepare for the
> evacuation as if the approaching hurricane will intensify one category
> above the strength forecast for landfall (Mercado 1994).
>
> E. The model accounts for astronomical tides (which can add
> significantly to the water height) by specifying an initial tide
> level, but does not include **rainfall amounts, river-flow, or
> wind-driven waves**. This information is however, combined with the
> model results in the final analysis of at-risk-areas (see Slide 23).
>
> F. The point of a hurricane\'s landfall is crucial to determining
> which areas will be inundated by the storm surge. Where the hurricane
> forecast track is inaccurate, SLOSH model results will be inaccurate.
> The SLOSH model, therefore, is best used for defining the **potential
> maximum surge** for a location.

#### 

#  G. The SLOSH Model has been calibrated and verified.

> 1\. After a SLOSH model has been constructed for a coastal basin,
> **verification experiments** are conducted (see Slide24). The
> verification experiments are performed in a "hind-cast" mode, using
> the real-time operational model code and storm parameters and an
> initial observed sea surface height occurring approximately 48 hours
> before the storm landfalls or affects the basin.
>
> 2\. The computed surge heights are compared with those measured from
> historical storms and, if necessary, adjustments are made to the input
> or basin data. In
>
> 3\. In instances where the model has given realistic results in one
> area of a basin, but not in another, closer examination has often
> revealed inaccuracies in the representation of barrier heights or
> missing values in bathymetric or topographic data.
>
> 4\. Ideally there would be a large number of actual storm events with
> well documented meteorology and storm surge histories which could be
> compared to the storm surge histories hind-cast by the SLOSH model for
> the same storms (see Slide 25).
>
> 5\. In reality, hurricanes are rare for any given region, and it is
> even rarer to find adequate, reliable measurement of storm surge
> elevations over a representative number of sites within a region due
> to the difficulty in making such measurement during hurricane
> conditions.
>
> 6\. The computed surge heights are compared with those measured from
> historic storms and, if necessary, adjustments are made to the SLOSH
> input or basin data .
>
> 7\. Adjustments are not made to force agreement between computed and
> measured surge heights from historical storms but to more accurately
> represent the basin characteristics or historic storm parameters.
>
> 8\. In the case of historic storms, most of the data has been coarse;
> with parameters prescribed invariant with time and with an
> unrealistically smooth storm track.
>
> 9\. When necessary, further analysis and subjective decisions are
> employed to amend the track or other parameters of the historic storms
> used in the verification process.
>
> 10\. Brian Jarvinen from the National Weather Service conducted a
> verification of the SLOSH Model with data collected during Hurricane
> Lili.
>
> 13\. Slide 26 shows a diagram of the extent of maximum and secondary
> winds for Hurricane Lili.
>
> 14\. Slide 27 shows the storm's path, maximum and secondary wind bands
> as well as the observed tide gage, high water marks, and SLOSH model
> outputs along the coast. The slide also provides a comparison of the
> observed and SLOSH model outputs for Hurricane Lili.

**Question:** A review of the recorded observations and SLOSH model
outputs from the National Weather Service shows that in some locations
there is from 1 to 4.5 feet difference in the height of the water. Do
you consider this to be a significant difference? Why? Should we be
concerned about the validity of the SLOSH model as run for Hurricane
Lili?

> *The SLOSH Model was designed to provide information to help public
> officials, private businesses and citizens make emergency planning and
> response decisions for hurricane wind and storm surge threats. For
> both emergency planning and response considerations, the SLOSH Model
> provided highly accurate estimates of the hurricane wind and storm
> surge hazards. Public officials could examine the threats associated
> with a hurricane and provide citizens with an assessment of the
> dangers posed by the storm. Accurate warning of the storm was possible
> with the model outputs; public officials could issue geographic
> specific evacuation orders well in advance of the storm.*
>
> *For Hurricane Lili, the greatest difference between the observed and
> modeled outputs occurred well outside the danger area for the storm.
> The error observed in Grand Isle, LA is significantly different from
> any other observation point in the study area and likely explained by
> the data inputs rather than the performance of the SLOSH model. NWS
> staff use the data recorded at Grand Isle to determine why the model
> outputs did not more closely describe the actual storm. For all other
> data points in the study, the results provided an accurate basis for
> emergency planning and response decisions. Decision makers are
> concerned about the validity of a model to accurately characterize the
> nature and extent of a hazard. The assessment of Hurricane Lili shows
> that the SLOSH Model provides extremely accurate model results for
> hurricane planning and response decisions.*
>
> 16\. The values or functions for the coefficients within the SLOSH
> model **are generalized** to serve for modeling **all storms** within
> **all basins** and are set empirically through comparisons of computed
> and observed meteorological and surge height data from numerous
> historical hurricanes (PowerPoint 10-6 Slide 9).
>
> H. Possible **sources of error** for SLOSH include (Mercado 1994):
>
> 1\. Noise in surge observations often exceeding = or -- 20%.
>
> 2\. The bathymetry given to SLOSH is not accurate.
>
> 3\. The topography given to SLOSH is not accurate.
>
> 4\. Errors in the initial water height.
>
> 5\. Wind wave effects, astronomical tidal effects, storm rainfall, and
> riverine flooding. These effects are often included in observed high
> water mark data used for verification.
>
> 6\. Noise in observed meteorological parameters. Sometimes it is the
> storm track which is a source of error.

I. Future uses of SLOSH

#### 

#### 1. Updates to the FEMA HAZUS-MH modeling and mapping tool will include a hurricane storm surge capability in the future. FEMA intents to provide a SLOSH like model that will allow emergency managers to model storm surge and estimate building losses. No date has been provided for the release of this utility for HAZUS-MH.

#### 

#### 2. Following Hurricane Katrina and Rita in 2005, FEMA worked with their flood modeling contractors to adapt HAZUS-MH to estimate building losses from flooding in New Orleans and Lake Charles, LA. Initial use of HAZUS revealed that the damage curves needed to be adapted because of the duration of the flooding in New Orleans. The latest release of HAZUS-MH in June 2006 allows the user to edit the damage curves so that estimated losses are a reflection of the actual damage from the storms.

#### 

J. Other Storm Surge Models

> Appendix A and B provide a summary of two additional storm surge
> models available to the emergency management community. Have the
> students review the two models and compare these models to SLOSH. The
> National Hurricane Center utilizes the ADCIRC model for internal
> purposes but provides the SLOSH model outputs to state and local
> agencies.

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Appendix A

HURREVAC

HURREVAC uses NWS forecast storm data and displays the track of a storm.
Using Hurricane Evacuation Study (HES) data, it derives the potential
for storm surge and calculates evacuation times based on storm speed and
intensity. It can also be used as a \"what-if\" tool to help emergency
managers determine courses of action for different storm
characteristics.

HURREVAC tracks hurricanes on computer plot maps using information from
the National Hurricane Center (National Weather Service, NOAA). Marine
advisories on tropical storms are normally issued by the National
Hurricane Center every six hours: 0500EDT, 1100EDT, 1700EDT, and
2300EDT. At times, intermediate advisories are also issued. These
advisories contain information on present and forecast position,
intensity, size, and movement that is displayed by HURREVAC. HURREVAC
estimates when various evacuation decisions should be made, using data
from the federal hurricane evacuation study for the areas. The process
is as follows:

1.  The arrival of tropical storm (34 knots or 39 mph) winds in your
    area is computed using the NHC projects with adjustment for a
    direct-hit or worst-case approach to your community.

2.  Clearance times are computed using Saffir-Simpson scale category of
    storm, response of the public, and occupancy readings for the area.
    The basic data for the clearance times is produced by a local
    Hurricane Evacuation Study, usually performed by the Corps of
    Engineers, National Weather Service and FEMA.. The clearance time is
    subtracted from the arrival of tropical storm force winds to reach a
    suggested evacuation decision time. This approach is based on the
    need to have the at-risk population out of vulnerable areas before
    tropical storms force winds reach the coast.

The HURRicane EVACuation program (HURREVAC) was developed by Sea Island
Software, Inc. was developed in response to a need for data to prepare
hurricane evacuation decisions.

These studies were produced for regions of the United States to assist
government emergency managers in making decisions for their
states/communities when under a hurricane threat.  

First major use of the program came with Hurricane Hugo (1989) in South
Carolina and Georgia.  Subsequently, the program was developed for 13
states, the US Virgin Islands and Puerto Rico.

HURREVAC tracks hurricanes using information from the National Hurricane
Center (National Weather Service, NOAA) and provides estimates of when
various evacuation decisions should be made, using data from the federal
hurricane evacuation study for the area.  

It is a **tool** that you may be used to help in the hurricane
decision-making process.

Hurrevac outputs may be exported in several GIS formats.

# 

1.  **A storm track *as points and lines*** -- Separate files are
    created for the two shape types and are differentiated by "\_p" and
    "\_l" tacked on to the end of the filenames. An exported storm track
    may include either the forecasted track from the current advisory,
    the past (actual) track derived from old advisories, or both the
    past and forecasted track. Nodes (in the line file) and points (in
    the points file) represent the initial positions of each advisory
    for the past track and the 0,12, 24, 36, 48, 72, 96, and 120-hour
    forecasted positions for the current advisory. The past and
    forecasted tracks are exported as 2 separate lines and attributed
    with "0" and "120" to represent their respective values. Points are
    attributed with a date/time field and a maximum wind speed field.

2.  **Wind ranges from any forecast hour (0-72) *as polygons*** -- Up to
    three rings with values of 39, 58, and 74 mph may be output.

3.  **Wind swath through hour 72 of current advisory *as polygons*** --
    Up to three polygons with values of 39, 58, and 74 mph may be
    output.

4.  **Error swath or error swath plus winds *as polygons* \--** Up to
    three polygons with a single attribute field indicating 72-hour
    average error (72), extended forecast average error (120), and
    average error plus winds (0).

5.  **Error ellipse (with or without winds) from any forecast hour
    (0-120) *as polygons*** -- One polygon (attribute value of 72
    or 120) for the error ellipse and a larger wind ellipse (attribute
    value of 0).

6.  **MEOW (Max Envelope of Wind) for specified region and storm
    conditions *as polygons*** -- Polygons are attributed with 39, 58,
    74, 92, 109, and 127 mph to indicate the maximum wind possible for
    the region.

7.  **HPC rainfall isopleths for specified day (1-3) *as polygons*** --
    Polygons have attribute values to indicate a region's expected
    rainfall in 100^th^ of inches.

8.  **NWS river flood outlook *as polygons*** -- Polygons have attribute
    values to indicate whether the likelihood of flooding in a region is
    possible (1), likely (2), or imminent or occurring (3).

**Appendix B**

## Advanced Circulation Model for Coastal Ocean Hydrodynamics (ADCIRC)

![](media/image1.png){width="2.6354166666666665in"
height="2.25in"}![](media/image2.png){width="2.6354166666666665in"
height="2.25in"}

#### ADCIRC is a natural hazard numerical model developed for the specific purpose of generating long time periods of hurricane storms along shelves, coasts, and within estuaries. The intent of the model is to produce long numerical simulations for very large computational domains in a unified and systematic manner.  Computational models of flow and transport in continental margin waters are used to predict free surface elevation and currents for applications ranging from evaluating coastal inundation, defining navigable depths and currents in near shore regions, to assessing pollutant and/or sediment movement on the continental shelf. 

#### 

The ability of these computer models to accurately represent the actual
waterbody physics depends on the flow processes and phenomena considered
in the calculation, the validity of the governing equations, the body
and boundary forcing functions, the scope of the computational domain,
the accuracy and robustness of the numerical algorithms, and finally the
temporal and spatial discretization applied in the calculation.\
\
It is certain that high spatial and temporal grid resolution is one of
the key factors in improving the accuracy of flow calculations in the
coastal ocean.\
\
ADCIRC has been extensively applied by both the U.S. Army and Navy for
tidal and hurricane storm surge predictions in regions including the
western North Atlantic, Gulf of Mexico and Caribbean Sea, the Eastern
Pacific Ocean, the North Sea, the Mediterranean Sea, the Persian Gulf
and the South China Sea. Other users of ADCIRC include governmental
agencies, consulting firms and university researchers for applications
ranging from real time hurricane storm surge predictions to impact
studies of sewage outfall placement.\
\
**ADCIRC** can be run either as a two-dimensional depth integrated
(2DDI) model or as a three-dimensional (3D) model. In either case,
elevation and velocity of the storm is calculated.

**Appendix C**

**Measurement Units**

NAUTICAL MILE: A unit of length used in marine navigation that is equal
to a minute of arc of a great circle on a sphere. One international
nautical mile is equivalent to 1,852 meters or 1.151 statue miles. Refer
to a sea mile.

MILLIBAR (MB): A metric measurement of atmospheric pressure used by the
National Weather Service.. Standard surface pressure is 1,013.2
millibars.

STANDARD SURFACE PRESSURE: The measurement of one atmosphere of pressure
under standard conditions. It is equivalent to 1,013.25 millibars, 29.92
inches of mercury, 760 millimeters of mercury, 14.7 pounds per square
inch, or 1.033 grams per square centimeter.

KNOT: A unit for the measurement of speed in the nautical system. It is
the nautical miles per hour.

STATUTE MILE: Commonly known as a ground mile.

PRESSURE: The force per unit area exerted by the weight of the
atmosphere above a point on or above the earth\'s surface. Also known as
atmospheric pressure or barometric pressure.

RAIN: Precipitation in the form of liquid water droplets greater than
0.5 mm. If widely scattered, the drop size may be smaller. It is
reported as \"R\" in an observation and on the METAR. The intensity of
rain is based on rate of fall. \"Very light\" (R\--) means that the
scattered drops do not completely wet a surface. \"Light\" (R-) means it
is greater than a trace and up to 0.10 inch an hour. \"Moderate\" (R)
means the rate of fall is between 0.11 to 0.30 inch per hour. \"Heavy\"
(R+) means over 0.30 inch per hour.

MEAN SEA LEVEL: The heights of the sea surface midway between its
average high and low water positions.

HURRICANE PATH OR TRACK: Line of movement (propagation) of the eye
through an area.

STORM TRACKS: The path or tracks generally followed by a cyclonic
disturbance.

SWATH: The width of the path of the hurricane. Usually this path area is
about 125 miles wide with 75 miles to the right of the eye and 50 miles
to the left of the eye.

## FEEDER BANDS: In tropical parlance, the lines or bands of thunderstorms that spiral into and around the center of a tropical system. Also known as outer convective bands, a typical hurricane may have three or more of these bands. They occur in advance of the main rain shield and are usually 40 to 80 miles apart. In thunderstorm development, they are the lines or bands of low-level clouds that move or feed into the updraft region of a thunderstorm.