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Meanest stretch of hurricane season begins

Hurricane season might seem pretty tame so far, particularly in light of the predictions for a highly active year.

Through the first seven weeks, a hurricane and two tropical storms have emerged, about average activity.

But the meanest stretch — the seven weeks from mid-August through early October — is here and "now the game starts," said Stanley Goldenberg, a research meteorologist with the National Oceanic and Atmospheric Administration.

Waters in the tropical Atlantic are heating up. The atmosphere in the deep tropics is becoming more moist. The upper-level winds are easing. And more robust tropical waves are rolling off the coast of Africa.

Possibly adding fuel, La Niña, the large scale atmospheric force that promotes storm formation, is kicking in, experts say. As a result, forecasters predict 18 to 20 named storms, including 10 to 12 hurricanes, will develop this season. They project five to six will be intense, with winds greater than 110 mph.

An average season sees 11 named storms, including six hurricanes, two intense.

Goldenberg said several seasons have started slow or average and ended up being extremely active.

For instance, in 1998, the first hurricane didn't form until late August. The season ended with 10 hurricanes, three major.

"People say in August, it sure seems quiet," said Goldenberg, who works for NOAA's Hurricane Research Division in Miami. "I say just wait, the season hasn't really gotten started."

He also noted that in highly active seasons, there is a 90 percent chance at least one hurricane will strike the U.S. East Coast.

"Of course, this says nothing about the impact to South Florida," he said. "However, in an active year, it is almost certain South Florida will at least get some threats or close calls."

On average, five hurricanes, including two major ones, form between mid August and the first week of October. However, since 1995, when the Atlantic basin entered an era of heightened intensity, many seasons have seen considerably more systems than that.

In 1995, for instance, seven hurricanes, four intense, developed in that time frame. In 1998, eight hurricanes, two intense, formed. And in 2005, eight hurricanes, three intense, emerged.

Just the same, forecasters expected more activity in June and July, and note unexpected levels of wind shear, dry air and Saharan dust acted to subdue systems.

Phil Klotzbach, the Colorado State University climatologist who works with William Gray, said an expansive system of low-pressure is largely responsible for creating the wind shear.

But that system starts to weaken at this time of year, he added.

"So we should expect conditions to become more conducive for storm formations over the next couple of weeks," he said.

Jeff Masters, chief meteorologist of Weather Underground, an online weather site, said another reason for the slow start might be the record heat on land areas creating dry air and stability over the adjacent oceans.

"It is also possible that climate change is causing the reduction in tropical cyclone activity, for a variety of complex reasons," he said.

But, he added: "I still think we will have a busy season. It just will be delayed, like the 1998 season was."

Other experts say a large ridge of high pressure over the Atlantic has pushed tropical systems so far to the south that they don't have enough "leverage" from the Earth's gravitational forces to spin up. But that ridge is expected to move farther north in coming weeks.

Although the busiest stretch of the season goes into early October, the rest of that month also could be active. Systems tend to develop in the western Caribbean, where water temperatures remain warm and wind shear low.

Goldenberg, of NOAA, said October can be just as busy as August in active years. He further noted that on average one major hurricane has formed every year in October since 1995.

"During a busy year, you do not let your guard down in October. All you have to say is Wilma," he said, referring to the hurricane that hit South Florida in late October 2005.

Goldenberg said there have been highly active years where the United States escaped seeing severe seasons, such as 1995. Meanwhile, there have been slow years where the U.S. coast got clobbered, such as 1992, when Hurricane Andrew destroyed much of South Miami-Dade County.

"The reminder to people is that we're predicting an extremely active year," he said. "Whether it is or not, it only takes one hurricane to cause a disaster."

Ken Kaye can be reached at kkaye@sunsentinel.com or 954-572-2085.

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