http://hosted.ap.org/dynamic/stories/H/HURRICANE_CYCLE?SITE=FLPEJ&SECTION=HOME&TEMPLATE=DEFAULT
Sep 17, 11:23 AM EDT
By JOSEPH B. VERRENGIA
AP Science Writer
Ivan, Frances and Charley delivered three staggering blows to the Gulf Coast and Florida, as well as Caribbean island nations, all in just five weeks. Now here comes Jeanne, which could be lashing north Florida and Georgia by Monday. Homeowners ritualistically re-hammering the same plywood over their windows figure it can't get much worse, right?
Brace yourselves: Scientists say 65 million Americans living on the Gulf and Atlantic coasts should expect weather like this for another 30 years. Maybe more.
Sure, it's hurricane season and storms happen. But counting Alex, which swamped the Carolinas in August, that's five in six weeks. And that doesn't include tropical storms Bonnie, Gaston, Earl and Hermine.
"I don't remember this happening before in such a short period of time," National Hurricane Center director Max Mayfield told reporters, "and the season is only half-over."
It might be a generation before hurricane weather slips back into a quiet phase, he and other experts say.
"The hurricane threat is much greater than it was in the 1970s through early 1990s," said federal meteorologist Stan Goldenberg, who flew around Hurricane Ivan in research aircraft as it approached Mobile, Ala. "It could last another 10 to 40 years."
Goldenberg and other experts believe the current hurricane surge is part of an obvious storm cycle that probably has been waxing and waning for hundreds of years.
Roughly from 1970-94, Atlantic hurricane activity in the United States was relatively mild. Sure, there were monster hurricanes like Andrew in 1992 - its 177 mph winds killed 55 people in the U.S. and Caribbean and caused $26.5 billion in damage. Every year a big storm whips up - it's just that most fizzle before veering into a city.
Overall, the 25-year "quiet" period generated about half as many destructive storms as the previous stormy phase dating back to the 1920s, and about half as many as today's stormy phase appears likely to produce.
Since 1995, environmental conditions have shifted and the Atlantic has been spawning more strong storms. The number of major hurricanes has more than doubled. In the Caribbean, it's up by a factor of five.
Even with milder storm years in 1997 and 2002, the period since 1995 is the most active nine consecutive years on record, according to pioneering hurricane forecaster William Gray at Colorado State University.
Since 2000, the United States has been hit by an average of four powerful storms per season.
Forecasters have been warning of this for years. Even back in 1998 - a year that saw four hurricanes in September - Gray said: "We are going to see the return of some of these type of storms. People have to face up to it. The insurance industry has a major problem."
Last month, Gray tweaked his gloomy 2004 forecast downward, predicting 13 named storms rather than 14. He expected seven storms to blow up into hurricanes, three with sustained winds of 111 mph or greater.
So far, he's right. If storms continue brewing, Gray might wish he had tweaked his forecast up, not down. And don't forget that last year, two more tropical storms developed in the Caribbean after the hurricane season formally ended Nov. 30.
Why is the storm cycle intensifying now? Scientists aren't certain what causes the decades-long shifts in the ocean-atmosphere interplay.
Hurricanes reflect the complex dance between the atmosphere and the oceans.
When the Pacific Ocean cools during the La Nina climate phenomenon, the Atlantic warms up, and more hurricanes are the result. Over the Atlantic, wind shear that knocks down rising storms tend to slacken, while humid westerly winds from Africa's bulge grow stronger.
Scientists look for large pools in subtropical ocean where water is at least 81 degrees Fahrenheit. The warm sea heats the air in a rising column, creating a center of moist low pressure.
Trade winds rush in toward this depression. Combined with the planet's rotation, they spin clouds counterclockwise around this steamy core, or "eye" of the storm.
Most scientists agree that global warming plays little or no role in the number of storms in the current hurricane cycle.
Global climate models show that air pollution from industry and traffic will drive up average world temperatures by a degree or two this century. All that extra heat could fuel more stormy weather. And local evidence of temperatures rising may already be apparent with some glaciers melting and spring flowers blooming early. But so far, climate change is too uncertain and today's hurricane patterns are too complex to draw a connection.
"I don't think the warming now is anywhere near enough to account for the increase in hurricanes that we're seeing," said Robert Gall of the National Center for Atmospheric Research in Boulder, Colo. "To me, this is just a natural variation in the frequency of hurricanes."
Hurricanes are among nature's most powerful natural events. Spinning as fast as a race car, the wall of clouds can rise 10 miles into the stratosphere and span 400 miles, as wide as Kansas.
The amount of mechanical energy generated by a such a swirling storm translates to a power supply of 360 billion kilowatt hours per day - equal, by some estimates, to all of the electricity consumed in United States in six months.
Only 12 percent of the world's swirling storms spawn in the Atlantic. About 100 of these cyclones are reported annually worldwide. Most of them crank unnoticed in the North Pacific and the Indian Ocean.
A large storm might seethe and spin for 3,000 miles, inhaling the energy from billions of tons of warm seawater. Incoming dry air from high pressure zones can choke it off, or landfall can quickly deflate it.
Forecasters are much less comfortable predicting how a storm will behave once it hits land. That's a major focus of their research now.
Ivan boasted 160 mph winds in the Gulf, but it quickly lost about half of its fury when it reached Alabama.
That's not always the case. Hurricane Charley whipped up to a category 4 storm when it hit Florida's west coast. Andrew was just a tropical storm in the hours before it hit Miami.
Goldenberg said it's harder to forecast storm intensity than to accurately predict its path.
Since coastal residents now heed hurricane warnings, researchers are turning their attention to an underappreciated danger - downpours reaching inland for hundreds of miles.
Ivan could dump 20 inches of rain as far away as North Carolina, weakening trees and foundations.
"Most deaths now come from freshwater flooding," said Gall, of the atmospheric research center. "If Ivan hovers over the Appalachians, it could be dramatic."
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