Titel:South Florida Sun-Sentinel v. 22.09.2005: KATRINA, RITA PART OF POWERFUL STORM CYCLE

South Florida Sun-Sentinel, 22 September 2005


FORT LAUDERDALE, Fla. - (KRT) - Hurricanes Katrina and Rita, the muscular headliners of this hurricane season, are just a preview of what to expect in coming years: More powerful storms.

And the trend could span decades.

Rita weakened slightly Thursday from a mighty Category 5 to a still-dangerous Category 4, but remained on course for the Texas coast, with an inevitably destructive landfall predicted for late Friday or early Saturday.

As the storm took a loose turn north, aiming somewhere between Galveston and the Texas-Louisiana border, more than a million threatened residents fled inland.

Floridians can expect similar scenarios as part of a natural cycle that will not only see more hurricanes, but more powerful ones as well.

"We are solidly into one of these active periods," said Colin McAdie, a meteorologist with the National Hurricane Center. "We're figuring we're 10 years into this one. We could be looking at 10 to 20 more years."

That means next year, and the years after that, could be just as scary as this one, with mega-storms taking aim at Florida, the Carolinas or the Gulf Coast, spiking the anxiety levels of those in their path.

Hurricanes feed on warm water and scientists say the pattern of increased storm frequency and strength is caused by a cyclical rise in ocean temperatures.

Besides fueling more powerful hurricanes, a higher number of storms means more of them will be stronger.

"Certainly, with more frequency of active systems, we can see a lot more chances to have more intense hurricanes," said another storm forecaster, Chris Sisko.

The cycles commonly run about 25 to 30 years, scientists say, but can vary and see breaks of as much as a decade. The current cycle started around 1995. Prior to then, from 1975 to 1995, only four major hurricanes, defined as a Category 3 or higher, impacted the state.

"In the `70s and `80s," McAdie said, "people were saying, `I guess we don't get hurricanes any more.'"

By contrast, 23 hurricanes hit South Florida alone during the last cycle of high hurricane activity, from 1926 to 1965. Of those storms, 15 were major ones. "We had about a 40-year period when it was very busy," said meteorologist Chris Landsea with the National Hurricane Center. During that cycle, on Labor Day 1935, a Category 5 hurricane hit the Florida Keys.

It's getting busy this cycle, too. Last year, four hurricanes, three of them Category 3 or higher, made landfall in Florida. This year, with two months yet to go in the season, two hurricanes, Dennis and Katrina, have already struck the state.

Rita, which boasted winds of 175 mph before weakening Thursday, was the third most intense Atlantic Basin hurricane on record.

After sideswiping Key West on Tuesday, the storm spun into the Gulf of Mexico, where it quickly sucked up energy from the warm waters of the Loop Current, a segment of the Gulf Stream that flows into the central Gulf from between Cuba and the Yucatan Peninsula.

By Thursday afternoon, however, forecasters said a wind shear, or strong upper level air flow, damaged the storm's top end, causing it to lose some power. The hurricane's slower pace over cooler water pockets also sapped its strength. While the storm was expected to pass over warmer water late Thursday night, the wind shear was also predicted to increase, possibly canceling out any regained strength.

Forecasters say it's possible the storm could drop a notch to a Category 3 hurricane, with winds of at least 111 mph, before it makes landfall. Hurricane center director Max Mayfield often says the difference between a Category 3 and Category 4 storm is like the difference between getting hit by a freight train or an 18-wheeler.

A cycle of warm ocean water fuels individual storms like Rita, and gives rise to stronger hurricanes during high activity cycles such as the present one. Researchers say a higher salt content in the Atlantic causes the water to become more dense, which in turn causes the water to grow warmer, perhaps by as much as a degree.

That single degree can make a difference in whether a tropical wave rolling across the sea will develop into a devastating hurricane.

Researchers have yet to decipher the rhythm of the storm cycles. "The oceanographers are looking into that, trying to understand that," Landsea said.

Contrary to speculation, the cycles may not result from human-induced global warming. Prevailing scientific opinion says global warming has little or nothing to do with the trend.

"The science is not settled on that," McAdie said. "It's an open question."

© 2005 South Florida Sun-Sentinel.


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