Hurricane Idalia sent the Gulf of Mexico surging up to 12 feet high on Florida coast

When Hurricane Idalia made landfall on the Florida coast on August 30, the Category 3 hurricane delivered a surge of sea water as much as 12 feet above normally dry ground, the National Weather Service has concluded in a preliminary report.

The hurricane's winds briefly reached 130 mph before making landfall with 125-mph winds near Keaton Beach. A weather service survey team found Idalia pushed water levels between 7-12 feet higher along more than 33 miles of coast to the north and south of the center.

The first Category 3 storm to make landfall on the sparsely populated coast in decades, Idalia devastated Gulf-front communities and damaged a swath of homes, businesses and forests between the Gulf and southern Georgia. Private insured losses from Idalia were preliminarily estimated at between $3 billion and $5 billion by Moody’s RMS, a Moody’s Analytics firm and international risk modeling company.

The report released Monday found the highest surge values from Dekle Beach in Taylor County south to Horseshoe Beach in Dixie County. The devastation could have been much worse, but a key factor worked in the region's favor.

Idalia arrived around the time of low tide, the weather service said. "Had the storm made landfall 6 hours later, around the time of high tide, peak water level values could have been 3-4 feet higher."

The devastating water inundated numerous structures along the coast, as well as homes and businesses many miles inland, the weather service said. Lower values of up to 6 feet above normally dry ground were found south of Horseshoe Beach near the community of Suwannee.

Surge may have rivaled 'Storm of the Century'

Several residents who lived in the area during the infamous "Storm of the Century" in March 1993 talked with the weather service team during the high water mark survey.

All the residents interviewed from Keaton Beach to Horseshoe Beach said Idalia's water levels "rivaled or exceeded" the 1993 water levels, the weather service said. Dixie County's Emergency Management pointed out the storm surge moved "much farther inland" from Horseshoe Beach than it did during the 1993 storm.

However, "it's still too early to state that definitively, the weather service said. It plans to compare surveys from the two events and make a determination later.

How is storm surge measured?

Once conditions were safe and emergency responders had completed search and rescue operations, a weather service field survey team studied homes within the surge zone to examine water and debris marks. Those marks helped them determine the still water level and wave water level.

• The still water level is the storm surge, the rise above normally dry ground.
• Traces of wave action can be found above still water levels.
• Wave action during Idalia averaged about three feet above the peak storm surge.

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Collecting other storm data

Live video from Steinhatchee helped to confirm the water levels, the weather service said.

The survey team also used data from a regional water management agency gauge 2.5 miles upstream from the mouth of the Steinhatchee River. That gauge showed a river height of about 8.03 feet, nearly a foot higher than during Hurricane Hermine.

The gauge recorded a six foot rise in one hour.

Further to the south, the weather service office in Tampa Bay reported the water level in Cedar Key, where Idalia also arrived at low tide, reached 6.89 above dry ground. Water levels reached as high as 3.2 feet in Fort Myers, more than 240 miles to the south.

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