The SLOSH (Sea, Lake, and Overland Surges from Hurricanes) Model computes storm surge heights from tropical cyclones. This computerized model estimates the overland tidal surge heights and winds that result from hypothetical hurricanes. SLOSH model coverage includes all of the U.S.'s East and Gulf coastline, as well as parts of Hawaii, Guam, Puerto Rico and the Virgin Islands. The East and Gulf Coastlines are broken into individual basins for study.

Graphical output from the model displays color coded storm surge heights for a particular area in feet above the model's reference level, the National Geodetic Vertical Datum (NGVD), which is the elevation reference for most maps.

The 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 from a predicted hurricane (as opposed to a hypothetical one), forecast data must be put in the model every 6 hours over a 72-hour period and updated as new forecasts become available.

Chesapeake Bay Basin

SLOSH takes several factors into account to calculate the potential height of water above the Mean Sea Level (MSL) in hurricane warning areas.

• Atmospheric pressure created by the hurricane
• Wind stress combined with elevation increases of the Continental Shelf
• Size of the hurricane
• The angle that the hurricane makes with the coastline
• The forward speed of the hurricane when it crosses the coastline
• The effect of land features such as underwater sills, channels and rivers.
• The effect of obstructions on land such as sand dunes, roads, levees, etc.

The items listed below are not included in the model simulations, but they may be combined with the model results for the final analysis of at-risk areas.

• Astronomical tides
• Rainfall amounts
• River flow
• Wind driven waves

What is the relationship between a hurricane's track and storm surge?

What is the relationship between a hurricane's size and storm surge?

What is the relationship between a hurricane's speed and storm surge?

With so many variables, SLOSH models are unable to predict the exact water height, although experience has shown that SLOSH models are fairly close. A good "rule of thumb" is that the actual water height will be within plus or minus 20 percent of the predicted. If the model calculates a storm surge of 10 feet for an event, then you should expect to see observed ranges of 8 to 12 feet (not including wave heights.) Many factors effect the storm surge from a hurricane, and no two storms are alike. If you live in a potential storm surge area, you should be prepared to evacuate if necessary. Storm surge is a very dangerous condition that causes loss of life and devastating property damage. Individuals living in storm surge areas are encouraged to consider purchasing flood insurance.

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 physical features. The model estimates open coastline heights as well as surge heights over land, thus predicting the degree of propagation or run-up of the surge into inland areas. 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. Therefore, the SLOSH model is best used for defining the potential maximum surge for a location.

What does a Surge Map tell me?