Hurricanes: Their Nature and Impacts on Society - Climate Science ...

HURRICANE IMPACTS
5.2.2 Storm surge analysis
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A storm surge can be deadly. In 1900, up to 12000 deaths occurred in
Galveston, Texas, primarily as a result of the storm surge that was associated
with a Gulf of Mexico hurricane (Chapter 1). In 1957, a storm surge, which
was associated with Hurricane Audrey <strong>and</strong> which was over 12 feet (3.5
meters) <strong>and</strong> extended as far inl<strong>and</strong> as 25 miles (40 kilometers) in this
particularly low-lying region, was the major cause of the death of 390 people
in Louisiana. In September 1928, the waters of Lake Okeechobee, driven by
hurricane winds, overflowed the banks of the lake <strong>and</strong> were the main cause of
more than 1800 deaths (Chapter 1).
Areas to be evacuated due to storm surge in the case of hurricane l<strong>and</strong>fall
are determined through a model developed by the National Weather Service
(NWS) called SLOSH (Sea, Lake, <strong>and</strong> Overl<strong>and</strong> Surges from <strong>Hurricanes</strong>;
Jarvinen <strong>and</strong> Lawrence 1985). The SLOSH model is used to define floodprone
areas in 31 "SLOSH basins" along the US Gulf of Mexico <strong>and</strong> Atlantic
coasts (Figure 5.2). Figure 5.3a shows Charleston, South Carolina, as a closeup
example of a SLOSH basin. Determination of storm surge vulnerabilities is
the result of an interagency <strong>and</strong> intergovernmental process funded by NOAA,
FEMA, Army Corps of Engineers, <strong>and</strong> various state <strong>and</strong> local governments
(BTFFDR 1995). From development through application the SLOSH process
takes about two years. Because coastlines are constantly changing due to
human <strong>and</strong> natural forces, the SLOSH process is never completed.
A SLOSH model is developed through a number of steps for each basin.
First, the Techniques Development Laboratory (TI])L) of the US National
Weather Service (NWS) obtains water depth <strong>and</strong> I l<strong>and</strong> height data for a
particular basin to input to the model. Second, the model is tested against
historical analogues in the basin, with model runs compared against empirical
data from past storms. Third, TDL, the National Hurricane Center (NHC),
<strong>and</strong> local officials refine the water depth <strong>and</strong> l<strong>and</strong> height data through
reconnaissance of the basin. They check for barriers such as highways in order
to improve the accuracy of the input data. Mter final testing for accuracy,
each SLOSH model is declared "operational" <strong>and</strong> is turned over to the NHC
for applications. I
Evacuation strategies based on the SLOSH model output are generally
developed in three phases. First, the NHC simulates between 250 <strong>and</strong> 500
hypothetical storms in each basin to develop a composite map of potential
storm surge inundation for various families of storms (based on strength,
movement, <strong>and</strong> point of l<strong>and</strong>fall). A composite map (called a Maximum
Envelope Of Water, or MEOW) is developed to compensate for errors <strong>and</strong>
uncertainties in the forecast track. Because the MEOW represents maximum
storm surge from several hundred storms, it compensates for any small
forecast error in the track of a particular approaching storm. In the second
phase. local NWS, state <strong>and</strong> local government, FEMA, <strong>and</strong> Army Corps of