Immediately after a storm, surge levels are hard to verify. A mix of tide data and visible high-water marks can give experts enough information to make a best guess, but they say they’re waiting for official data before being certain of anything.
Hurricane Idalia was poised to bring up to 7 feet of storm surge to the Tampa Bay area. As the storm sped up while it tracked north and shifted west Tuesday, peak surge warnings in the area fell to a prediction of up to 5 feet.
If preliminary data is proven to be accurate, East Bay Tampa would hold a new surge record for the Tampa Bay area after receiving what is believed to be nearly 5.7 feet.
Other parts of Tampa Bay experienced dangerous storm surge that destroyed homes and left residents stranded. The area remained under a storm surge warning until a 5 p.m. update Wednesday from the National Hurricane Center.
Homes in Shore Acres and mobile homes around St. Petersburg saw extreme flooding from the surge. Local landmarks were closed due to high water: Police officers turned people away from the St. Pete Pier, and the Dalí Museum entrance was submerged in a foot of water.
By early afternoon, 2 feet of surge still blocked roads in some parts of Tarpon Springs and Clearwater.
Rodney Wynn, a forecaster with the National Weather Service’s Tampa Bay office, said the area should have seen the worst of the storm by Wednesday afternoon.
“We’re seeing the water levels starting to drop as well,” Wynn said. “So, that’s good news for everybody.”
St. Petersburg experienced a “king tide,” the highest tide of the year, just before 2 p.m. Wednesday. Even as the tide rose, water levels dropped across much of the area.
St. Petersburg experienced 4 feet of storm surge, Mayor Ken Welch said Wednesday morning. This would put Idalia’s surge on par with the city’s current record, set in 1985, but researchers say this data could change in the coming days.
“Nothing’s official yet,” Wynn said. “This is just preliminary, first-look numbers that we have so far.”
Preliminary data shows Welch’s number isn’t far from the mark: The St. Petersburg tide gauge showed near-record surge of 3.82 feet. If confirmed, the reading would be the second-highest on record, surpassed only by 4-foot surge from Hurricane Elena in 1985.
Data from the Clearwater Beach tide gauge appears to set a new storm surge record of about 5.3 feet for the city. If verified, it would beat the 4.02 feet observed in 1993′s “Storm of the Century,” according to Jeff Masters, a hurricane scientist formerly with the National Oceanic and Atmospheric Administration.
He said these surge records are best measured in feet above “mean higher high water,” a standard, above-ground-level measurement.
Masters expects the records Idalia is believed to have set in Tampa Bay to hold up when they are officially verified.
“Those tide gauges are pretty rock solid,” he said.
Monthly data from these stations is typically verified during the first week of the following month.
But these numbers can be unreliable when it comes to official record-setting, said Brian McNoldy, a senior research associate at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.
“The odds of a tide gauge recording the peak storm surge is really slim,” he said.
McNoldy said because the stations use outdated baseline levels, these recordings don’t account for sea level rise, which could lower the official readings by about 4 to 6 inches.
In the coming days, National Weather Service teams will be looking at hundreds of high water marks on buildings around Tampa Bay to get a better sense of Idalia’s peak surge, McNoldy said.
“We don’t know the answers,” he said. “That’s definitely not something that’s going to come around right away.”
So how likely is it that this early data could set new storm surge records?
“It certainly stands a chance,” McNoldy said.
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