Zeta’s Strong Waves Will Cause Coastal Change Along the Gulf Coast

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Editor’s note: This story was updated Oct. 28 reflecting a new coastal change forecast for Zeta's impacts on Gulf Coast sandy shorelines.

A new U.S. Geological Survey coastal change forecast predicts sandy beaches in Louisiana and Mississippi may be heavily damaged by Zeta, which is expected to make landfall Oct. 28 as a hurricane. Sandy beaches in Texas, Alabama and Florida may see moderate to minor damage. The Oct. 27 forecast will be updated whenever the National Hurricane Center’s surge forecasts for Zeta change. The most current forecast is always available on the USGS Coastal Change Hazards Portal.

The USGS coastal change forecast can help 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.

Louisiana and Mississippi are expected to bear the brunt of the storm’s strong waves and surge, with 23% of Louisiana's and 16% 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 impact coastal communities. The areas currently projected to be inundated are from Marsh Island, Louisiana, to Biloxi, Mississippi. Texas, Alabama and Florida are not projected to have beaches inundated by Hurricane Zeta.

The second worst type of coastal damage is called overwash and occurs when waves and surge reach higher than the top of dunes. Approximately 60% of sandy beaches along Louisiana’s coast and 46% of Mississippi’s beaches are expected to be overwashed by Zeta. About 11% of Alabama’s beaches and 1% of beaches in Bolivar Peninsula, Texas. Florida’s beaches are not predicted to be overwashed. When a beach is overwashed, sand can be deposited inland, causing significant changes to the landscape. Overwash can reduce the height of protective 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. In Louisiana, 68% of sand dunes from Marsh Island to the Mississippi state line are projected to be eroded by Zeta. In Mississippi, 89% of dunes will likely erode along with 57% in Alabama, 24% in Texas and 1% in Florida.

Zeta is the 27th named storm during the historically active 2020 Atlantic Hurricane Season. Upon landfall it will become the 11th named storm to strike the U.S. this year, a new record for a single season. While Zeta is less intense than some earlier 2020 storms, the National Hurricane Center is currently forecasting life-threatening storm surge along parts of the Gulf coast.

“Zeta might be a small storm but it can still cause a lot of coastal change along the Gulf, especially since the area the storm is currently heading toward has already been hammered by several storms this year,” said oceanographer Kara Doran, leader of the USGS Coastal Change Hazards Storm Team.

The prediction of Zeta’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 model starts with inputs from the NHC’s storm surge predictions and National Oceanic and Atmospheric Administration wave forecast models. It then adds detailed information about the expected landfall region’s beach slope and dune height. The predictions define “very likely” effects as those that have at least a 90% 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 to Zeta, 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.