On Monday, national forecasters predicted Tampa Bay’s centurylong streak of hurricane luck was about to end.
One forecaster called the storm a “potential historic catastrophe.” The region was looking at 10 feet of storm surge. Billions in property damage. Untold destruction, unmitigated catastrophe.
Two days later, the disaster has arrived — for Tampa Bay’s neighbors about 75 miles to the south. Once again, the forecasters in the federal government were unable to perfectly nail the track of a major hurricane.
Meteorologists say there were multiple reasons. Forecasters accurately predicted that a low pressure system would push Ian to the east, but it was difficult to know how far. The uncertain strength and speed of the storm itself also affected how it interacted with the weather systems pushing it along its path.
Any small change in track would — and did — mean a big difference in impact for Florida’s densely populated Gulf Coast.
Phil Klotzbach, a research scientist in Colorado State University’s department of atmospheric science, likened a hurricane like Ian to a pebble in a stream. Outside factors steer major storms to their eventual destination.
Perhaps the biggest factor steering Ian: A low pressure system disrupting the jet stream air current, which blows from west to east at high altitudes. Scientists knew a pressure system in the western Gulf of Mexico would create a U-shaped trough in wind patterns. Ian, headed north into the right side of the trough, would be forced east. But even within the pivotal trough, there were variations in pressure that had the potential to change the course of the storm.
“Some very subtle little ripples along that large scale weather system were key in determining what eventually happened to Ian,” said Jeff Masters, the meteorologist for Yale Climate Connections, who said on Monday he feared catastrophe for Tampa Bay.
Ian also turned out to be stronger and faster than many scientists predicted. The models factored in a phenomenon called shear, in which dueling winds affect the structure of the hurricane’s vortex. In the Atlantic, winds near the ocean surface blow out of the east, Klotzbach explained. Higher up, they blow out of the west. When the winds blow across a hurricane at different speeds, it can tilt the vortex, making it harder for a storm to strengthen.
In an area of low shear, storms have the ability to gather and intensify. When Ian was forming in the Caribbean, it did so in a low-shear environment.
As Ian moved northeast through the Gulf of Mexico Tuesday and Wednesday, it encountered an area of moderate shear and warm water. Forecasters figured the storm would strengthen but also that the shear would mitigate its ferocity.
The shear appears to have had little effect. Ian fed on the warmer water Tuesday night and surged toward the Gulf Coast as a near-Category 5 storm.
“The storm blew up a lot faster than people were anticipating,” Klotzbach said.
Because of how Florida’s Gulf Coast is situated and the angle at which Ian approached, scientists didn’t have to be off by much in their forecast in order to be off by a lot in terms of human impact.
But Klotzbach noted forecasters still performed fairly well in one respect: Monday’s prediction of a Tampa Bay landfall came with caveats that Ian’s track would be hard to predict.
And Masters noted the storm still landed within the cone of uncertainty forecasters projected earlier in the week. That’s impressive, he argued, given the cone is only intended to depict two-thirds of the potential storm scenarios.
“They did a darn good job with this forecast,” Masters said.
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2022 Tampa Bay Times Hurricane Guide
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WHAT TO EXPECT IN A SHELTER: What to bring — and not bring — plus information on pets, keeping it civil and more.
SAFEGUARD YOUR HOME: Storms and property damage go hand in hand. Here’s how to prepare.
IT’S STORM SEASON: Get ready and stay informed at tampabay.com/hurricane.
RISING THREAT: Tampa Bay will flood. Here's how to get ready.
DOUBLE-CHECK: Checklists for building all kinds of hurricane kits
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