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This nowCOAST™ map service provides maps depicting the latest official NWS Potential Storm Surge Flooding Map for any significant landfalling tropical cyclone expected to impact the Atlantic or Gulf of Mexico Coasts of the Contiguous United States. The map layers depict the risk associated with coastal flooding from storm surge associated with tropical cyclones.
The Potential Storm Surge Flooding Map depicts the geographical areas where inundation from storm surge could occur along with the heights, above ground, that water could reach in those areas. These potential heights are represented with different colors based on water level: 1) Greater than 1 foot above ground (blue), 2) Greater than 3 feet above ground (yellow), 3) Greater than 6 feet above ground (orange), and 4) Greater than 9 feet above ground (red). Two versions of this graphic are provided in this map--one with a mask (depicted in gray) identifying Intertidal Zone/Estuarine Wetland areas, and another version without the mask where Intertidal Zone/Estuarine Wetland areas are symbolized with the same colors as other areas.
Two additional layers are provided to depict 1) the full geographic extent for which the Potential Storm Surge Flooding Map is presently valid (the "map boundary"), and 2) Levee Areas, if any, within the affected area (symbolized with a black-and-white diagonal hatch pattern).
If the Potential Storm Surge Flooding Map is not presently active, all layers will be blank except for the Map Boundary layer, which will display a shaded region indicating the coverage area for any potential future graphics along with a text label indicating that the map is not presently available.
This map service is updated approximately every 10 minutes on nowCOAST™ to ensure the latest information is provided to the user as soon as it becomes available. Once issued, the Potential Storm Surge Flooding Map will be updated by NHC every six hours alongside each new Forecast Advisory for the associated tropical cyclone. However, due to processing requirements during the creation of this product, the flooding map becomes available approximately 60 to 90 minutes following the release of the associated NHC Forecast Advisory, at which point nowCOAST™ will acquire it and update this map service within the next 10 to 20 minutes (i.e., this product will be updated on nowCOAST™ within approximately 70 to 110 minutes after the associated Forecast Advisory is released). For more detailed information about layer update frequency and timing, please reference the nowCOAST™ Dataset Update Schedule.
Developed by National Hurricane Center (NHC) over the course of several years in consultation with social scientists, emergency managers, broadcast meteorologists, and others, the Potential Storm Surge Flooding Map is intended to depict the risk associated with coastal flooding from storm surge associated with tropical cyclones. On June 1, 2016 it became an operational product, issued on demand for certain tropical cyclones that are expected to affect the Atlantic and Gulf Coasts of the United States. The product is not available for tropical cyclones that may affect coastal areas in the Eastern or Central Pacific regions.
From the NHC Website:
"What the Map Takes into Account
The Potential Storm Surge Flooding Map is based on the NWS Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model and takes into account forecast uncertainty in the tropical cyclone track, intensity, and wind field. The map is based on probabilistic storm surge guidance developed by the NWS Meteorological Development Laboratory (MDL), in cooperation with NHC, called Probabilistic Hurricane Storm Surge (P-Surge 2.5).
P-Surge 2.5 derives storm surge probabilities by statistically evaluating a large set of SLOSH model simulations based on the current NHC official forecast, and takes into account historical errors in the official NHC track and intensity forecasts. P-Surge 2.5 combines the results of hundreds of individual SLOSH simulations to calculate the statistical distribution, or probabilities of possible storm surge heights at locations along the coast. All major factors that influence the amount of storm surge generated by a storm at a given location are accounted for, including the hurricane's landfall location, forward speed, and angle of approach to the coast; the storm intensity and wind field; the shape of the coastline; the slope of the ocean bottom; and local features such as barrier islands, bays, and rivers. The Potential Storm Surge Flooding Map is created by processing the resulting 10 percent exceedance levels from P-Surge 2.5, or storm surge values that have a 1-in-10 chance of being exceeded at each location.
The Potential Storm Surge Flooding Map takes into account:
- Flooding due to storm surge from the ocean, including adjoining tidal rivers, sounds, and bays
- Normal astronomical tides
- Land elevation
- Uncertainties in the landfall location, forward speed, angle of approach to the coast, intensity, and wind field of the cyclone
The Potential Storm Surge Flooding Map does not take into account:
- Wave action
- Freshwater flooding from rainfall
- Flooding resulting from levee failures
- For mapped leveed areas - flooding inside levees, overtopping of levees
Potential storm surge flooding is not depicted within certain levee areas, such as the Hurricane & Storm Damage Risk Reduction System in Louisiana. These areas are highly complex and water levels resulting from overtopping are difficult to predict. Users are urged to consult local officials for flood risk inside these leveed areas. If applicable to the region displayed by the map, these leveed areas will be depicted with a black and white diagonal hatch pattern.
The intertidal zone, or generally speaking, the area that is above water at low tide and under water at high tide, will be displayed with a user selectable mask layer on the Potential Storm Surge Flooding Map. Locations of estuarine wetlands, or lands that are saturated with water, either permanently or seasonally, are also used to help define this mask layer. This mask layer will allow users to differentiate between areas that could experience consequential flooding of normally dry ground and areas that routinely flood during typical high tides. The intertidal mask will be depicted as gray on the Potential Storm Surge Flooding Map.
What the Map Represents
The Potential Storm Surge Flooding Map represents the storm surge heights that a person should prepare for before a storm, given the uncertainties in the meteorological forecast. The map shows a reasonable worst-case scenario (i.e., a reasonable upper bound) of the flooding of normally dry land at particular locations due to storm surge. There is approximately a 1-in-10 chance that storm surge flooding at any particular location could be higher than the values shown on the map. Roadways are included in the basemap layer for aiding in geographical referencing only. The map will not indicate which roadways may flood from fresh or salt water in a hurricane situation."
This nowCOAST™ map service is not time-enabled.