Subject: F7) How is storm surge forecast at NHC?
The Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model is the computer model utilized by the National Oceanic and Atmospheric Administration (NOAA) for coastal inundation risk assessment and the operational prediction of storm surge.
The eastern seaboard and Gulf Coast of the United States, Puerto Rico, the Bahamas, the Virgin Islands, and Hawai’i, are subdivided into 39 regions or “basins.” These areas represent sections of the coastline that are centered upon particularly susceptible features: inlets, large coastal centers of population, low-lying topography, and ports. The SLOSH model computes the maximum potential impact of the storm in these “computational domains” based on storm intensity, track, and estimates of storm size provided by hurricane specialists at NHC.
Currently, SLOSH basins are being updated at an averate rate of 6 basins per year. SLOSH basin updates are ultimately governed by the Interagency Coordinating Committee on Hurricanes (ICCOH). ICCOH manages hazard and post-storm analysis for the Hurricane Evacuation Studies under FEMA’s Hurricane Program. Updates are driven by a number of different factors such as: changes to a basin’s topography/bathymetry due to a hurricane event, degree of vulnerability to storm surge, availability of new data, changes to the coast, and addition of engineered flood protection devices (e.g. levees).
Sometimes these updates include higher grid size resolution to improve surge representation, increasing area covered by hypothetical tracks for improved accuracy, conversion to updated vertical reference datums, and including the latest topography or bathymetric data for better representation of barrier, gaps, passes, and other local features.