The role of the SLOSH model in National Weather Service storm surge forecasting

The storm surge model, Sea, Lake, and Overland Surges from Hurricanes (SLOSH), is used by the National Weather Service (NWS) in producing storm surge guidance in several ways. SLOSH is run by the National Hurricane Center (NHC) to forecast storm surge in realtime when a hurricane is threatening. The model is applied to 38 specific coastal areas, called basins, along the Atlantic and Gulf of Mexico coasts of the U.S.; Oahu, Hawaii; Puerto Rico; and the Virgin Islands. SLOSH is also used to create simulation studies to assist in the "hazards analysis" portion of hurricane evacuation planning by the Federal Emergency Management Administration (FEMA), the U.S. Army Corps of Engineers, and state and local emergency managers. Two composite products, Maximum Envelopes of Water (MEOW) and Maximum of the MEOWs (MOM), are created to provide manageable datasets for planning. The Probabilistic Storm Surge model (P-surge) overcomes the limitations of a single deterministic SLOSH storm surge forecast by being comprised of an ensemble of SLOSH forecasts. The members of the ensemble vary in speed, direction, intensity, and size, based on NHC's forecast and past errors associated with NHC's forecasts. P-surge is prompted to run when NHC issues a hurricane watch for the Atlantic or Gulf coasts. The Extratropical storm surge (ET surge) model uses SLOSH to forecast storm surge from extratropcial cyclones. The ET surge model uses surface wind and pressures that are generated by NWS's Global Forecast System (GFS) model as driving forces.