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St. Petersburg Coastal and Marine Science Center > Coastal Change Hazards: Hurricanes and Extreme Storms > Hurricane Wilma

Coastal Change Hazards: Hurricanes and Extreme Storms

Potential Coastal Impacts

Hurricane Wilma

Assessment of Potential Coastal Impacts

For more information about the Storm Impact scale and the first line of defense, see the Storm-Impact Scale section.

Posted Thursday, October 20, 2005

As of the 2:00 PM National Hurricane Center (NHC) forecast, the sandy beaches along the west coast of Florida are within the cone of uncertainty for the path of Hurricane Wilma. The long, thin barrier islands that comprise the Gulf of Mexico coast of west Florida are particularly vulnerable to inundation during hurricanes because of their low elevation. In a cooperative research program between the U.S. Geological Survey, NASA, and the U.S. Army Corps of Engineers, these islands have been surveyed using airborne laser mapping (lidar) providing detailed elevation maps of the island's 'first line of defense', essentially the Gulf-front dune (or in the absence of dunes, the crest of the beach berm or seawall).

Maps showing the spatial variability of where worst-case storm surge exceeds the 'first line of defense' elevations for Saffir-Simpson Categories 1 through 5 hurricanes for the beaches along the west coast of Florida.
Maps showing the spatial variability of where worst-case storm surge exceeds the 'first line of defense' elevations for Saffir-Simpson Categories 1 through 5 hurricanes for the beaches along the west coast of Florida. The red areas (positive inundation) indicate where the potential storm surge is higher than the 'first line of defense' elevation, suggesting those parts of the coast may be inundated by storm surge. Green indicates where surge is lower than the 'first line of defense' elevations, suggesting those areas are less vulnerable to inundation. The red areas will be inundated only if subjected to the indicated surge, which this coast typically occurs to the south of the eye at landfall and will decrease with distance along the coast from the eye wall. These estimates assume landfall occurs at mean astronomical tide and do not include changes in island elevation due to erosion during the storm. [larger version]

The maps above show where the 'first line of defense' would be inundated by worst-case storm surge associated with different category hurricanes. The storm-surge elevations were obtained from NOAA and represent the maximum simulated surge that will result along the open coast from hurricanes of a given category approaching from different combinations of direction and forward speed. On Florida's west coast barrier islands, the maximum surge will typically occur to the south of landfall near the eyewall and will decrease with distance away from the eyewall. Consequently, the worst case for any given storm is localized and does not occur along the entire coast.

When the dune is overtopped by storm surge-such as would occur for most of the Florida west coast if impacted by the south eyewall of a Category 3, 4, or 5 hurricane-strong currents drive potentially massive amounts of sand landward across the island (Storm Impact Scale for Barrier Islands, Impact level 4 of the Coastal Change Hazard Scale). These currents sometimes scour new inlets, as happened during 2004's Hurricane Charley on the southwest coast of Florida.

The modeled storm surge values do not include the effects of tides or waves. The tide stage at landfall could either raise (high tide) or lower (low tide) the actual surge. The presence of waves will increase the reach of the ocean further inland.

Note: This experimental product is based on research results of the USGS National Assessment of Coastal Change Project and applies to potential changes to the coast (e.g. erosion) caused by storm surge, ocean waves and associated currents. The vulnerability assessment does not directly consider potential property damage or the impacts of high wind speeds and heavy rain. The actual changes that occur to the coast during extreme storms are complex functions of a number of processes and variables. This discussion simplifies the problem to some of the most important aspects, but a full analysis of all processes will be required to fully understand the magnitudes and spatial variability of storm-induced coastal change of Hurricane Wilma.


Related links:

Storm Impact Scale
USGS

Monitoring Hurricane Wilma's Storm Surge
Sound Waves Article

St. Petersburg Coastal and Marine Science Center > Coastal Change Hazards: Hurricanes and Extreme Storms > Hurricane Wilma

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