A Hurricane Is Saving the U.S. from a Tropical Storm

"Last Friday the forecasts were highly uncertain about Imelda's path and future strength: the possibilities ranged from the storm making landfall in the Carolinas, which would bring torrential rain and floods, to it not making landfall in the U.S. The latter now looks to be the likely scenario. That's because Imelda dawdled in its development while Humberto quickly exploded into a major hurricane, which has influenced how much the two storms feel each otheressentially a flavor of what is called the Fujiwhara effect."

"The higher-than-usual level of forecast uncertainty can be explained partly by the fact that storms in the Atlantic don't typically form this close to each other. Tropical cyclones are influenced by the larger atmospheric environment, and adding another storm system makes that environment more complex. Meteorologists were also unclear about exactly where the center of Imelda would ultimately form, which made it difficult to know how that center would interact with other features in the atmosphere."

Imelda and Hurricane Humberto have been churning between the Bahamas and Bermuda, with Humberto rapidly intensifying into a major hurricane. Imelda's slow development and Humberto's strengthening produced a Fujiwhara-like interaction that altered Imelda's trajectory, making U.S. landfall less likely. The East Coast remains vulnerable to rip currents, and Bermuda could face a threat as Imelda turns sharply eastward. Forecast uncertainty increased because two storms formed unusually close together and because the precise center of Imelda was unclear, complicating predictions of how it would interact with atmospheric pressure and wind patterns in three dimensions.

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