King Tide timing raises Hurricane Idalia’s flood threat for Florida Gulf Coast
When Hurricane Idalia churns into Florida’s Gulf Coast sometime early Wednesday, unusually high tides will likely raise the storm surge flooding risks for many small communities that dot the Big Bend region.
Forecasters at the National Hurricane Center predict peak surge could rise as high as 15 feet in the area between the Aucilla River and Yankeetown, which includes parts of Taylor, Dixie and Levy counties. But the ultimate height of the surge will depend heavily on the tides, which can bring significant swings in sea level during the King Tide season. Water levels can vary by as much as five feet, higher and lower, with the ebb and flow of King Tides.
“It’s close to the full moon and the tidal system is in just the right place to make extra high high tides and extra low low tides,” said Mark Luther, an associate professor of oceanography at the University of South Florida. “The timing of the storm passing relative to the tides is critical for determining who’s going to get flooded and who’s not.”
Read More: Florida braces for Hurricane Idalia. 125 mph winds, 15-foot storm surge expected
Unfortunately for the Gulf Coast, the tides on the morning of Aug. 30 — when Idalia is expected to make landfall and bring the peak of its storm surge — will be higher than usual. Even the low tide that morning will be between 7 and 19 inches higher than average low tides at points around the Big Bend, according to tidal predictions from the National Oceanic and Atmospheric Administration (NOAA).
The high tides in some spots are expected to rise as much as 3.5 feet above typical low tide levels Wednesday morning. “If the storm surge hits around that low tide, then there will be less coastal flooding,” said Luther, “but if the max storm surge hits close to one of those high tides, then we’re going to have an extra 3.5 feet of water.”
In many spots around the Big Bend, NOAA predicts Tuesday night’s low tide will be an unusually low “negative tide,” which means it’s lower than the average low tide. Had the storm struck during a negative tide, lower sea levels would have brought down the height of the storm surge. Instead, the storm will strike the next morning, when the low tide is predicted to be a foot or two higher than tonight.
Read More: Florida’s Gulf Coast is vulnerable to storm surge. Idalia is pushing up to 15 feet of it
In Cedar Key, an island city that juts into the sea right in the middle of the area that is forecasted to see the highest storm surge, the tides are expected to be somewhere between 1.6 and 3.5 feet above the average low tide on the morning of Aug. 30, when the storm will likely make landfall.
The height of all tides has steadily crept up over the past several decades thanks to climate change. Sea levels in Florida have risen about 8 inches since 1950, according to the Florida Climate Center, and scientists expect them to keep rising over the next several decades.
“It makes a bigger difference for lesser storm surge events,” said Florida state climatologist David Zierden. “If you have a 15-foot storm surge and you add 10 inches to it, it’s still going to be pretty darn catastrophic either way. But if you had a two-foot storm surge and then you add another 10 or 12 inches, all of a sudden you’ve increased its damage potential by 50 percent.”
“Sea level rise is and will continue to make storm surge more destructive,” he said.
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