Hurricane modellers got it wrong last weekend, when hurricane Charley swerved right at the last minute, unexpectedly intensified and devastated the town of Punta Gorda on Florida鈥檚 west coast. 鈥淚t鈥檚 very humbling,鈥� says meteorologist John Kaplan of the National Oceanic and Atmospheric Administration鈥檚 Hurricane Research Division in Miami, who develops models for predicting hurricane intensity. 鈥淪ometimes you just want to throw up your hands and say 鈥楯eez, I don鈥檛 know鈥�.鈥�
With winds of about 230 kilometres per hour, Charley killed at least 20 people and injured many others. It was classified as a category 4 hurricane, and was the worst to hit the US since hurricane Andrew struck Florida in 1992.
Charley was predicted to make landfall 110 kilometres further north, but changed direction within minutes of crossing the coast. 鈥淚t strengthened by about 55 kilometres per hour over six hours, and that鈥檚 very rare,鈥� Kaplan says. A similar increase in wind speeds over 24 hours is normally considered a rapid intensification.
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Winds at an altitude of 30,000 to 40,000 feet probably steered the hurricane southwards, and may have contributed to Charley鈥檚 strength. These winds are responsible for steering all weather systems. This time, however, there was a particularly deep trough in the windfield, Kaplan says. 鈥淲e have some data that suggests it may have played a role.鈥�
An above-average number of eight hurricanes are predicted to hit the US this season, but the trend has been for fewer hurricanes over the past century.