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Forecasts again out of kilter

But this time it's a lack of storms that has undermined the early predictions. Forecasters now are expecting little more activity.

By GRAHAM BRINK
Published October 4, 2006

ST. PETERSBURG - Predicting the number of hurricanes once again has proved perplexing.

In 2005, a record-setting 28 named storms almost doubled the original forecasts.

This year, though, it's a lack of storms that has undermined the early season projections.

The discrepancies show just how much more scientists need to learn about what causes the subtle changes that can turn what looks to be a busy season into an average one and vice versa, said Robert Weisberg, a marine sciences professor at the University of South Florida.

"It's not that hard to make a prediction," Weisberg said. "It's hard to get it really right."

Before the season began on June 1, the top hurricane forecasters predicted up to 17 named storms. So far this year, only nine have formed, and the outlook for October and November is slow as well.

On Tuesday, longtime hurricane researcher William Gray and his protege, Philip Klotzbach, again downgraded their predictions, calling for just two more named storms in October and none in November.

Klotzbach explained that the predictions are based on statistics, which can't account for every factor that influences the environment in which storms form.

"The atmosphere and ocean are inherently chaotic," he said.

Several factors conspired to flummox forecasters and suppress storms this year.

Sea surface temperatures in the Atlantic Basin - the Atlantic Ocean, Caribbean Sea and Gulf of Mexico - were down from last year. Warm waters help fuel storms.

The atmospheric pressure was higher and the air was drier with a high level of dust from Africa. Wind shear was also stronger, which helped rip apart storms before they could start.

And last month, scientists announced that El Nino had formed rapidly. The phenomenon, which remains difficult to predict, involves the movement of warm surface waters from the western Pacific to the eastern Pacific. It encourages upper-level winds that thwart the formation of hurricanes or reduce their intensity.

Many forecasts call for this El Nino to strengthen into the winter.

"It came on very quickly and later in the year than normal," Klotzbach said.

The few storms that have formed stayed away from the U.S. mainland or weakly limped ashore. No hurricanes have made landfall in the United States so far this year.

Atmospheric physicist Steve Smith, who leads catastrophe modeling efforts for Carvill, a reinsurance company, correctly predicted earlier this year that the Bermuda High would help steer many storms away from the United States this season.

The Bermuda High, a huge mass of high pressure that moves around the Atlantic during the year, set up to the east. The position created an "alley" between the system's western edge and the U.S. mainland for the storms to travel harmlessly out into the north Atlantic.

Some years, the Bermuda High sets up closer to the United States, pushing storms ashore.

Given the position of the Bermuda High and the other factors suppressing storms this year, Smith didn't foresee any major threats to the United States for the remainder of the season.

"I think we have pretty much seen the end of hurricane season," he said.

Graham Brink can be reached at brink@sptimes.com or 727 893-8406.

[Last modified October 4, 2006, 05:40:00]