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Katrina may not be hurricane-season finale
San Francisco Chronicle


September 01, 2005

As bad as Hurricane Katrina is, it may not be the last such devastating storm of what promises to be a ferocious hurricane season through much of autumn, meteorologists say.

The Gulf, Florida and East coasts could also be in for a decade or more of similar coastline-battering storms, they say. And, according to some experts, global warming might be generating much more intense hurricanes than in the past.

In their seasonal hurricane forecast issued earlier this year, William Gray and his colleagues at Colorado State University estimated that the odds were one-third higher than normal of a major hurricane making landfall on the Gulf Coast from Pensacola, Fla., to Brownsville, Texas.

To some, that forecast appears to have been grimly vindicated by this week's destruction and flooding of much of New Orleans and surrounding regions.

"This year, we were forecasting one of the most active seasons on record, " Gray research associate Philip Klotzbach said in an e-mail. "So yes, I guess I would say that we are not surprised that there have been landfalling hurricanes so far this year. ... And the season is only about 40 percent done."

Other experts are more cautious. Chris Davis of the National Center for Atmospheric Research in Colorado said it was too early to say that Gray's team had forecast the New Orleans storm.

"A probabilistic forecast cannot be vindicated by a single event," Davis said. "The quality of Dr. Gray's prediction, when phrased in terms of probabilities, must be evaluated over many seasons."

Meteorologists say the kind of hurricanes that were common in the mid-20th century appear to be reviving because of quasi-cyclical variations in the atmosphere or ocean, or both.

With fortunate simultaneity, their hurricane forecasts have improved during the same period. One advance is the discovery of subtle atmospheric relationships between the rate of Atlantic-hurricane formation and the appearance or nonappearance of El Nino events, unusual oceanic warmings in the Pacific.

When El Nino events occur, few hurricanes strike, whereas hurricanes are more common when El Nino events are absent. This year, there has been an absence of El Nino.

Atlantic hurricanes are especially common when Atlantic waters are unusually warm, meteorologists also found. That also has been true this year.

Forecasters typically define "hurricane season" as June 1 to Nov. 30.

Gray's predictions are significant because many scientists regard him as the leading hurricane forecaster.

His "forecasts have had the longest track record and been the most skillful," said professor Lian Xie, a hurricane expert at North Carolina State University.

Still, hurricane forecasting remains a chancy business. Gray's forecasts "have been right in some years, but wrong in some other years," Xie said. But even Xie and his colleagues, as well as experts from the U.S. National Oceanic and Atmospheric Administration (NOAA), forecast this year's rough hurricane season.

If their forecasts hold up, more trouble is ahead before the season ends. Experts expect one or two more hurricanes to make landfall on the East Coast, plus other hurricanes that will whiz by without touching the coastline.

Gray also fears that the current cycle of severe hurricanes will persist for a few decades. That's because, if past records of ocean-temperature fluctuations are any guide, Atlantic waters will remain warm for a long time to come.

Kerry Emanuel, a hurricane specialist at the Massachusetts Institute of Technology, suspects that the revival of major, coastline-clobbering hurricanes in recent years is linked to human-caused global warming of the atmosphere.

In the Aug. 4 issue of the journal Nature, Emanuel reported an apparent 50 percent increase in the intensity of Atlantic and Pacific hurricanes (typhoons, as they are known in the Pacific) since the 1970s.

"My results," Emanuel said, "suggest that future warming may lead to an upward trend in (hurricanes') destructive potential, and - taking into account an increasing coastal population - a substantial increase in hurricane-related losses in the 21st century."

Gray and others have rejected this view, which has also been voiced by environmental activists. Still, Stephan P. Nelson, program director of physical and dynamic meteorology at the U.S. National Science Foundation, said Emanuel has an excellent reputation. "His paper should and will be taken seriously by the research community," Nelson said.

One critic, Chris Landsea, a research meteorologist at NOAA, said there was no evidence that the hurricane activity of recent years was dramatically different from that of the last century.

"The last few years have been busy (with hurricanes), but the 1930s to 1960s were much more destructive (as measured by wind speeds) than the last 10 years," Landsea said. "That points to the conclusion (that) we're not seeing more destructive hurricanes. I wouldn't claim there's no global-warming influence on (hurricane) activity, but I would agree that any such global-warming influence will be pretty small in the future."


Distributed by Scripps Howard News Service,

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