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The National Storm Surge Hazard Map is a risk analysis tool authorized by the National Hurricane Program (NHP) under the Stafford Act for the purposes of developing Hurricane Evacuation Studies and other hurricane planning and mitigation activities. This mapping dataset provides a more user friendly, seamless national map of near worst case storm surge flooding scenarios using the National Weather Service (NWS) SLOSH model Maximum of MEOWs (MOMs) product for Category 2 hurricanes at a HIGH tide scenario. The map adopts the GIS/Mapping process used for the National Hurricane Centers (NHC) real-time Potential Storm Surge Flooding map. However, this is not the real-time Potential Storm Surge Flooding map product.
Storm Surge Hazard Maps: https://www.nhc.noaa.gov/surge/nationalsurge/ SLOSH Model: https://www.nhc.noaa.gov/surge/slosh.php Potential Storm Surge Flooding Map: https://www.nhc.noaa.gov/surge/inundation/ National Hurricane Program, Hurricane Planning and Response: https://www.fema.gov/emergency-managers/risk-management/hurricanes/ |
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The National Storm Surge Hazard Map is a risk analysis tool authorized by the National Hurricane Program (NHP) under the Stafford Act for the purposes of developing Hurricane Evacuation Studies and other hurricane planning and mitigation activities. This mapping dataset provides a more user friendly, seamless national map of near worst case storm surge flooding scenarios using the National Weather Service (NWS) SLOSH model Maximum of MEOWs (MOMs) product for Category 2 hurricanes at a HIGH tide scenario. The map adopts the GIS/Mapping process used for the National Hurricane Centers (NHC) real-time Potential Storm Surge Flooding map. However, this is not the real-time Potential Storm Surge Flooding map product.
Storm Surge Hazard Maps: https://www.nhc.noaa.gov/surge/nationalsurge/ SLOSH Model: https://www.nhc.noaa.gov/surge/slosh.php Potential Storm Surge Flooding Map: https://www.nhc.noaa.gov/surge/inundation/ National Hurricane Program, Hurricane Planning and Response: https://www.fema.gov/emergency-managers/risk-management/hurricanes/ |
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Data processed by the National Hurricane Center (NHC) Storm Surge Unit. The primary elevation data used to compute inundation is provided by the NOAA Office for Coastal Management (OCM) and the USGS 3D Elevation Program (3DEP) is used outside the extent of OCM data. |
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The Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model is a numerical model used by NWS to compute storm surge. Storm surge is defined as the abnormal rise of water generated by a storm, over and above the predicted astronomical tides. Flooding from storm surge depends on many factors, such as the track, intensity, size, and forward speed of the hurricane and the characteristics of the coastline where it comes ashore or passes nearby. For planning purposes, the NHC uses a representative sample of hypothetical storms to estimate the near worst-case scenario of flooding for each hurricane category.
SLOSH employs curvilinear polar, elliptical, and hyperbolic telescoping mesh grids to simulate the storm surge hazard. The spatial coverage for each SLOSH grid ranges from an area the size of a few counties to a few states. The resolution of individual grid cells within each basin ranges from tens to hundreds of meters to a kilometer or more. Sub-grid scale water features and topographic obstructions such as channels, rivers, and cuts and levees, barriers, and roads, respectively, are parameterized to improve the modeled water levels.
NHC provides two near worst case scenario planning products based on hypothetical storm tracks: Maximum Envelopes of Water (MEOWs) and Maximum of Maximums (MOMs). MEOWs are created by computing the maximum storm surge resulting from up to 100,000 hypothetical storms simulated through each SLOSH grid of varying forward speed, radius of maximum wind, intensity (Categories 1-5), landfall location, initial water level, and storm direction. A MEOW product is created for each combination of category, forward speed, storm direction, and initial water level. SLOSH products do not include Category 5 storms north of the NC/VA border. For each storm combination, parallel storms make landfall in 5 to 10 mile increments along the coast within the SLOSH grid, and the maximum storm surge footprint from each simulation is composited, retaining the maximum height of storm surge in a given basin grid cell. No single hurricane will produce the regional flooding depicted in the MEOWs. SLOSH model MOMs are an ensemble product of maximum storm surge heights. MOMs are created for each SLOSH basin by compositing all the MEOWs, separated by category and initial water level, and selecting maximum storm surge value for each grid cell regardless of the forward speed, storm trajectory, or landfall location. The MOMs represent the worst case scenario for a given category of storm and initial water level under ideal storm conditions. A high tide initial water level was used for the storm surge hazard maps. This product uses the expertise of the NHC Storm Surge Unit to merge the operational SLOSH grids to build a seamless map of storm surge hazard scenarios using the MOM product. Each individual SLOSH grid for the Category 1-5 MOMs are merged into a single, seamless grid. The seamless grid is then resampled, interpolated, and processed with a Digital Elevation Model (DEM, i.e. topography) to compute the storm surge hazard above ground for each hurricane category. It should be noted that the SLOSH MOM storm surge hazard data used to create these maps are constrained by the extent of the SLOSH grids users should be aware that risk due to storm surge flooding could extend beyond the areas depicted in these maps. The resulting dataset is then reclassified into the bins described in the entity overview. The areas marked with a value of "99" represent certain levee areas, such as the Hurricane and Storm Damage Risk Reduction System in Louisiana. These areas are highly complex and this product should not be used to assess the storm surge hazard within these areas. Users are urged to consult local officials for flood risk inside these levee areas. Not all levee areas are included in this analysis - in particular, local features such as construction walls, levees, berms, pumping systems, or other mitigation systems found at the local level may not be included in this analysis. |
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The data and maps in this tool illustrate the scale of potential flooding, not the exact location, and do not account for erosion, subsidence, sea-level change, or future construction. Water levels are based on storm surge and high tide scenarios. The data, maps, and information provided should only be used as a tool for general education/awareness of the storm surge hazard at a city/community level (not for a parcel level or grid cell assessment) or should be used for analyses specified by the National Hurricane Program (NHP). The SLOSH MOM storm surge hazard data used to create these maps are constrained by the extent of the SLOSH grids and users should be aware that risk due to storm surge flooding could extend beyond the areas depicted in these maps. The data and maps in this tool are provided "as is", without warranty to their performance, merchantable state, or fitness for any particular purpose. The entire risk associated with the results and performance of these data is assumed by the user. This tool should be used strictly as a planning reference and storm surge risk awareness tool and not for navigation, permitting, or legal purposes. Consult local officials for evacuation decision making. |
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Va_Category2_MOM_Inundation_HighTide_v3_polys_wm |
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["storm surge","storm surge flooding","storm surge risk","National Hurricane Center","SLOSH","SLOSH MOMs","inundation","tropical cyclones","hurricanes"] |
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en-US |
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