Layer: CAT1_HurricaneStormSurgeRiskMaps

Parent Layer: Flood risk - NOAA NHC Gulf2Maine SLOSH

Name: CAT1_HurricaneStormSurgeRiskMaps_HighTide

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Description: National Hurricane Center - National Storm Surge Hazard Maps - https://www.nhc.noaa.gov/nationalsurge/The SLOSH (Sea, Lake, and Overland Surges from Hurricanes) 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.This is version 3 of the NHC National Storm Surge Risk Maps. The updates in this version include data mapped to 10m DEMs for the US Gulf and East Coast. The following new regions have been added: Southern California (hurricane wind category 1 and 2 storms), Guam, American Samoa, and the Yucatan Peninsula for parts of Mexico, Belize, and Honduras. For simplicity, the tiled map services are published by hurricane wind category and all available mapped regions for that category are provided in that web map.The following areas are mapped in the hurricane wind Category 1 Maps:US Gulf and East CoastPuerto Rico and US Virgin IslandsSouthern CaliforniaHawaiiGuamAmerican SamoaHispaniolaYucatan Peninsula- parts of Mexico, Belize, Guatemala, and western HondurasSLOSH 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.The NHC provides two products based on hypothetical hurricanes: MEOWs and 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, tide level, and storm direction. A MEOW product is created for each combination of category, forward speed, storm direction, and tide level. SLOSH products exclude Category 5 storms north of the NC/VA border. SLOSH products only include hurricane wind Category 1-4 scenarios for Hawaii and hurricane wind category 1-2 scenarios for Southern California. 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. These are called MEOWs and no single hurricane will produce the regional flooding depicted in the MEOWs. SLOSH model MOMs are an ensemble product of maximum storm surge heights. SLOSH MOMs are created for each storm category by retaining the maximum storm surge value in each grid cell for all the MEOWs, regardless of the forward speed, storm trajectory, or landfall location. SLOSH MOMs are available for mean tide and high tide scenarios and represent the near worst-case scenario of flooding 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 DEM (Digital Elevation Model, i.e. topography) to compute the storm surge hazard above ground for each hurricane wind category. 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.Users of this hazard map should be aware that potential storm surge flooding is not depicted within some 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. 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. Additionally, some marshy or low lying areas are not mapped in this analysis.In locations that have a steep and narrow continental shelf, wave setup can be a substantial contributor to the total water level rise observed during a tropical cyclone. Wave setup is defined as the increase in mean water level due to momentum transfer to the water column by waves that are breaking or otherwise dissipating their energy. The following locations use SLOSH+Wave Setup simulations to create MEOW and MOM products that account for the increase in the mean water level due to wave setup: Puerto Rico, US Virgin Islands, Hawaii, Hispaniola, Guam, American Samoa, and Southern California. Through the USAID/WMO Coastal Inundation and Flooding Demonstration Project, these SLOSH storm surge risk products were created for the Island of Hispaniola.

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Layer: CAT1_HurricaneStormSurgeRiskMaps_HighTide (ID: 36)