Powerful Dean Bolsters Busy Hurricane Season Forecasts

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Keith Blackwell, a hurricane researcher at the University of South Alabama's Coastal Research Center in Mobile, said the high-pressure system in the U.S. kept Dean from curving more to the north.

Most hurricanes in the Caribbean make that northward turn, Blackwell pointed out. But the so-called Bermuda high kept the storm's track "almost straight as an arrow" to the Yucatán.

"A hurricane can't move into a high-pressure system—it has to move around it," Blackwell said.

The high-pressure system is expected to weaken soon and bring a break from the intense heat. But that could be happening at a bad time. Without the hot weather, hurricanes could be more likely to curve into the U.S. coast, Blackwell said.

Harbinger of Busy Season?

Blackwell and Colorado State University forecaster Phil Klotzbach also think Hurricane Dean may be an indication that the rest of the hurricane season will be busy.

Klotzbach said Dean grew from a tropical wave—a moving region of low air pressure—that came off the west coast of Africa earlier this month.

"When you get a major hurricane from the easterly tropical waves in August, that tends to imply that the rest of the season will be fairly active," Klotzbach said.

Those waves roll off Africa during the late summer at or near the Cape Verde Islands (see a map of Cape Verde). As they move eastward across the Atlantic Ocean, they can develop into hurricanes.

Hurricanes that form in this manner often become very powerful, and these storms are referred to as Cape Verde hurricanes.

Hurricane Ivan, a devastating hurricane that made landfall as a Category 3 storm near Pensacola, Florida, in September 2004, was a Cape Verde storm.

"Dean was very much a Cape Verde system, along the lines of Ivan," Klotzbach said.

Klotzbach and CSU meteorologist William Gray predicted earlier this month that four intense hurricanes will form before the hurricane season ends on November 30.

No Clues on Warming

Hurricane Dean is the sixth Category 5 hurricane to form since 2003, and that fact has some meteorologists wondering if global warming is causing more frequent and more intense hurricanes. (Related: "Hurricanes Have Doubled Due to Global Warming, Study Says" [July 30, 2007].)

Some experts say the increase in hurricanes since 1995 is caused merely by a natural cyclical increase in the salt content of the Atlantic. The salt makes the water warmer and causes more storms to form.

But scientists on both sides of the debate don't think any conclusions can be drawn from just Hurricane Dean.

"It's impossible to talk about any individual weather event and its connection to the climate," said Kerry Emanuel, a meteorologist at the Massachusetts Institute of Technology who is a leading advocate of the theory that global warming is affecting hurricane formation.

"It's too much of a stretch to make a connection between global warming and one event," Emanuel said.

CSU's Klotzbach, who does not believe there's a link between global warming and hurricanes, agrees with Emanuel about not relying on Dean as an indicator.

"You can't take any one system and draw conclusions about climate change," Klotzbach said. "That's something we all can agree on."

Willie Drye is the author of Storm of the Century: The Labor Day hurricane of 1935, published by National Geographic.

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