Idalia may have brought record storm surge. Here’s why the region is so vulnerable
Residents and officials have always known: It does not take much to flood Tampa Bay.
The region experienced severe storm surges and widespread flooding in the wake of Hurricane Idalia this week, despite being more than 100 miles from the eye of the storm. Preliminary water measurements suggest a possible surge record: The East Bay gauge in Tampa recorded surge levels at nearly 5.7 feet.
It’s been more than 100 years since a major storm hit Tampa Bay directly, but the region’s geography and development have always made it especially vulnerable to storm surge.
Most of Tampa Bay’s highest flood events coincided with hurricanes or tropical storms that grazed the area before making landfall elsewhere.
Before Idalia, the record high at Clearwater Beach was 4.02 feet above “mean higher high water,” or the average height of the highest tide recorded each day. The record was set in March 1993 during the Storm of the Century, a superstorm that affected most of Florida’s Gulf Coast. At the St. Petersburg gauge, where more data is available, the surge that day was recorded at 4.1 feet above predicted levels.
The record water level at the St. Petersburg gauge is about 4 feet above MHHW. It happened Aug. 31, 1985, when Hurricane Elena swooped near Tampa Bay before making landfall near Biloxi, Miss. Its second highest – before this week – was 3.58 feet on Oct. 8, 1996, when Tropical Storm Josephine hit not far from Idalia’s landfall in Taylor County.
At the East Bay monitor, a record level of 3.8 feet above MHHW occurred Nov. 12, 2020 – the day Hurricane Eta brushed by the region as a tropical storm before heading toward Cedar Key, about 90 miles away.
It’s not unusual that Tampa Bay is prone to flooding even in non-direct hits, experts say. The shape of the continental shelf around the Gulf of Mexico traps high waters during north-moving storms, meaning any storm could cause flooding all along its coastline.
“It’s like a giant stepping into a bathtub,” said Jeff Masters, a former NOAA hurricane scientist.
Wind speeds are also a factor. Slow-moving storms like Elena are more likely to cause higher water levels at gauges in the bay, because there is more time to pound water inside and trap it there.
Meanwhile, storms with faster winds cause more flooding to communities on the open coast by shoveling and pushing water into the shoreline. A quick change of wind during 1993′s Storm of the Century, for instance, caused the system to whip along the coast and bring higher surges to Clearwater.
As far as Idalia’s likely record-breaking surge, Masters said the unique combination of especially high tides was particularly poor timing. The fact that surges occurred at mid-tide rather than high-tide, however, saved the region from even more severe flooding.
A Times analysis in 2021 found that up to 20% of Pinellas County properties could flood from Category 1 hurricanes – an issue exacerbated by continued development in flood-prone areas.
Sea levels are rising everywhere, but since 2010, they are increasing at triple the global rate in the Gulf of Mexico, Masters said. Given this trend, along with the warming waters that exacerbate storm intensity, it is increasingly possible that Tampa Bay residents could see surges up to 25 feet if the region is hit by a Category 4 or 5 storm.
“They should be prepared for the worst,” he said.
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