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A new U.S. Geological Survey coastal change forecast predicts some sandy beaches in Mississippi may be heavily damaged by Hurricane Sally, while beaches in Louisiana, Alabama and Florida may see moderate to minor damage. The forecast released on Monday will be updated whenever the National Hurricane Center’s surge forecasts are changed. The most current version is always available on the USGS Coastal Change Hazards Portal.

The USGS coastal change forecast can help local emergency management officials decide which areas to evacuate, where and when to close coastal roads, and where to position clean-up equipment in advance of the storm.

Mississippi is expected to bear the brunt of the storm’s strong waves and surge, with 36% of Mississippi’s sandy beaches forecast to be inundated, or continuously covered by ocean water. This is the most severe type of storm effect on coastal beaches, with flooding behind the dunes that may affect coastal communities. Louisiana and Alabama beaches will also encounter some inundation with 7% of Louisiana’s and 1% of Alabama’s beaches projected to be inundated. Hurricane Sally’s coastal erosion effects are expected to occur mostly from Breton National Wildlife Refuge in Louisiana through Alabama beaches west of Mobile Bay.

The second worst type of coastal damage is called overwash and occurs when waves and surge reach higher than the top of dunes. Sixty-one percent of sandy beaches along Mississippi’s coast are expected to be overwashed by Sally, while 21% of Lousiana’s and 14% of Alabama’s beaches will be overwashed. When a beach is overwashed, large amounts of sand can be deposited inland, causing significant changes to the landscape. Overwash can reduce the height of the coast’s protective line of sand dunes, alter the beaches’ profile, and leave areas behind the dunes more vulnerable to future storms.

The least severe level of storm damage on sandy shorelines is erosion at the base of sand dunes. All of Mississippi’s sandy shorelines, 63% of Alabama’s and 14% of Louisiana’s are predicted to erode at the dunes’ base. Only 1% of Florida’s sandy shorelines are expected to be eroded by Sally.

Sally is the fourth tropical cyclone to affect Gulf Coast beaches since the Atlantic Hurricane Season began June 1, and comes less than three weeks after powerful Hurricane Laura made landfall near Cameron, Louisiana Aug. 27.

“This certainly has been an active season for named storms impacting Gulf Coast states, with Cristobal, Marco, Laura and now Sally,” said USGS oceanographer Kara Doran, USGS Coastal Change Hazards Storm Team leader. “Most of the coastal impacts from Hurricane Sally will be farther east than the areas recently impacted by Hurricane Laura and will likely have a landfall area similar to Tropical Storm Cristobal.”

Doran warned that Sally’s size and intensity makes it a potentially more dangerous storm than Cristobal, which made landfall in Eastern Louisiana June 7.

“There was some coastal damage from Cristobal that probably made many of the beaches now in Sally’s path more vulnerable,” Doran said. “But it’s difficult to know for certain. With so many storms back to back in the same area, we’re not able to update the beach and dune height information that are used for our forecast models. While we don’t yet have the most up-to-date coastal elevation data to put into our model, our forecast is still a good indicator of what Sally is likely to do along the Gulf Coast.”  

The prediction of Sally’s effects at landfall is based on results of the USGS Coastal Change Forecast model, which has been in use since 2011 and is continually being improved. The Coastal Change Forecast model starts with inputs from the National Hurricane Center’s storm surge predictions and National Oceanic and Atmospheric Administration wave forecast models. The USGS model then adds detailed information about the forecasted landfall region’s beach slope and dune height. The predictions define “very likely” effects as those that have at least a 90 percent chance of taking place, based on the storm’s forecast track and intensity. 

As the USGS continues to take all appropriate preparedness actions in response Hurricane Sally, those in the storm's projected path can visit Ready.gov or Listo.gov for tips on creating emergency plans and putting together an emergency supply kit.