Hurricane season gets an early start

Andrea, the first named storm of 2007, appeared well ahead of the June 1 start date of the Atlantic's official season.

By Peter N. Spotts | Staff writer of The Christian Science Monitor

from the May 11, 2007 edition

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What was Andrea, the first named storm of 2007, doing off the Georgia coast, so far ahead of the official June 1 start date of the Atlantic hurricane season?

The early appearance of a subtropical storm like Andrea has happened before, though it's somewhat unusual. Storms of this type can even evolve into full-blown hurricanes, but Andrea was expected to dissipate this weekend.

Still, Andrea's emergence gives scientists an opportunity to study the storm's unusual features – its early timing, its formation outside the usual tropical-storm-incubation zone – to gain a better understanding of a class of storm that until recently has been overlooked and, therefore, difficult to forecast accurately.

The challenge of forecasting storms like Andrea – which carried tropical-storm-force winds and lashing rains – stems in part from the fact that they originate outside the tropics, in places forecasters aren't looking. Many have their genesis in mid-latitude storm systems coming off the North American continent, which masks their formation. As a result, forecasters have sometimes underestimated their intensity and failed to give adequate warning to areas subsequently hit hard.

Occasionally, subtropical cyclones can appear in unexpected places. A storm that crossed Lake Huron in September 1996 came to be known informally as "hurricane Huron." Like Andrea, it evolved out of a continental storm system. It displayed the high winds, tightly formed eye, and rain bands typical of tropical cyclones.

Although subtropical cyclones appear in various guises in other ocean basins, "the Atlantic basin seems to receive these subtropical-type storms with the most frequency," says James Elsner, a geography professor and tropical-cyclone specialist at Florida State University in Tallahassee.

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