Storms delivered differing blows

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In little more than a week’s time, Harvey and Irma showed us just how different hurricanes can be.

Harvey basically stalled over Houston and recharged with warm Gulf of Mexico waters, feeding days of rainfall that topped 4 feet. The storm surge in Galveston Bay, Texas, was barely 2 to 3 feet, and wind was not a big factor. Harvey will be remembered for record rainfall.

Irma came with a storm surge close to 10 feet in Everglades City, Fla. That storm struck with 110-mph winds and gusts recorded at 142 mph. Irma’s positioning and counterclockwise rotation pulled in water from the Atlantic Ocean on Florida’s east coast, creating a surge that looked like whitewater rapids in areas of the upper Florida Keys and the Brickell Point neighborhood of Miami.

If Irma had stayed on its predicted track and lingered off Florida’s Gulf coast, its eastern wall could have sent 15 feet of storm surge into Fort Myers, Tampa and St. Petersburg.

Irma’s Category 4 winds were also strong enough to push Tampa Bay waters out into the Gulf of Mexico. Photos show people walking on the bay’s mud bottom and manatees being stranded, waiting for wind to let water refill the bay. Instead of fearing a surge such as the one that hit Florida’s Atlantic coast, locals to the west hoped the bay would return to normal levels and float their boats off the bottom.

“Because of the circulation of the storm, the east coast had an onshore wind, creating higher than normal water levels, and if you’re on the west coast you get the negative storm surge,” says Hal Needham, founder and president of Marine Weather & Climate in Galveston, Texas. “Western Florida kind of lucked out.”

Because Florida is a peninsula, a properly positioned storm such as Irma can affect both sides of the state in different ways and at different times. Just as folks in Tampa and Fort Myers breathed a collective sigh of relief, the storm moved north and east and showed it wasn’t done, flooding St. Augustine and Jacksonville. The St. Johns River set a record, cresting at 5.57 feet above normal, breaking the mark of 4.12 feet that Hurricane Dora set in 1964.

Coastal Georgia and Charleston, S.C., also saw a damaging surge, with a National Oceanic and Atmospheric Administration tidal gauge in the latter peaking at 7.5 feet.

As with any major weather event, although most people were grateful that their homes were spared, others complained about the forecasting. They were not pleased that they had followed evacuation recommendations and gotten caught in traffic jams and fuel shortages before they were allowed to return to homes that were primarily unscathed.

Officials defended the forecasts. Susan Buchanan, acting director of public affairs at the National Weather Service, says the agency’s storm surge predictions 

were accurate for both Florida coasts. Needham also says the predictions were good, even if less water than expected ended up in neighborhoods full of homes.

“The eye of the storm came right over Naples,” Needham says. “If the eye of the storm had been 10 miles west, it would have been much more storm surge.”

Ken Kunkel, a researcher with the North Carolina Institute for Climate Studies, says a few miles can make a big difference when it comes to local effects.

“It shows, number one, the difficulty of forecasting hurricane tracks exactly if you’re several days away and several thousand miles away,” he says.

Look at it this way, Needham and Kunkel say: If you were taking a 10-hour road trip and you arrived 15 minutes late, you’d believe you planned it pretty well.

“If you think about it, the right turn that Irma took just south of Florida, that was forecast a number of days ahead of time,” Kunkel says, “and where it happened was not that far off from where it was predicted.”

This article originally appeared in the October 2017 issue.

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