Models and Observations
NOAA models storm surge to determine risk
Because there are many factors that affect surge, scientists have developed computational models that allow NOAA to simulate many different storms. Forecasters use the output as guidance for forecast products issued by the National Weather Service.
NOAA's hurricane storm surge model is called SLOSH, for "Sea, Lake and Overland Surges from Hurricanes." The National Hurricane Center (NHC) and local weather forecast offices use SLOSH output to assess coastal flooding risks and to predict storm surge heights from tropical cyclones. SLOSH is also the basis for the P-Surge probabilistic storm surge predictions generated for tropical cyclones.
The Extratropical Storm Surge (ETSS) model is also based on the SLOSH model. Four times a day, forecasters use to create storm surge forecasts for extratropical systems in the continental U.S. and Alaska. NOAA also uses the Extratropical Surge and Tide Operational Forecast System (ESTOFS) to predict the combined effects of storm surge and tides for extratropical systems on the U.S. east coast and Gulf of Mexico, as well as Puerto Rico.
The National Weather Service predicts wind waves using the model WAVEWATCH III®. This model covers the entire globe and mariners use it to assess conditions at sea. The Weather Service is coupling WAVEWATCH III® with high-resolution local wave models to increase detail along the coast.
With this suite of models, the Weather Service provides estimates of the height and extent of storm surge flooding. The National Hurricane Center and Central Pacific Hurricane Center use this information when issuing hurricane advisories. Emergency managers and other officials use this information to determine which coastal areas should evacuate due to potential storm surge threats. NOAA also continues to develop new models that will improve predictions in the future.
NOAA monitors storm surge conditions
NOAA's National Ocean Service monitors real-time water levels to assess storm surge conditions at stations throughout the United States and its territories. They use several methods to measure these water levels, with each method having its own advantages and disadvantages. In addition, the Center for Operational Oceanographic Products and Services (CO-OPS) provides the national infrastructure, science, and technical expertise to monitor, assess, and distribute tide, current, water level, and other coastal oceanographic products and services that support NOAA's mission.
NOAA uses these various methods and observations to issue website alerts on high water conditions caused by severe storms.
The importance of vertical datums
A vertical datum is an established surface that serves as a reference to measure or model heights and depths. All water level observations, including modeled storm surge heights, are referenced as height above a vertical reference datum. It is important when comparing water level observations (e.g. tide stations) with other observations, observations with models, or models to models, one MUST always use consistent vertical datums. NOAA has created a vertical datum transformation tool called VDatum that converts between different datums.
Currently, the SLOSH model utilizes the National Geodetic Vertical Datum of 1929 and the North American Vertical Datum of 1988. All SLOSH basins are being updated to the 1988 version. Other storm surge models may be referenced to different datums, such as mean sea level.