Sunday, May 28, 2000

TRACKING THE STORMS
Don't bet the farm on forecasts

By KEVIN HORAN

Herald Staff Writer



A look back at the 1999 storms

Storm Dates Highest Category Top Winds (mph) U.S. Deaths
Arlene June 11-18 Tropical Storm 58 0
Bret Aug. 18-25 Category 4 144 0
Cindy Aug. 19-31 Category 4 138 0
Dennis Aug.24- Sept.7 Category 2 104 4
Emily Aug. 24-28 Tropical Storm 52 0
Floyd Sept. 7-17 Category 4 155 57
Gert Sept. 11-23 Category 4 150 0
Harvey Sept. 19-22 Tropical Storm 58 0
Irene Oct. 13-19 Category 2 109 8
Jose Oct. 17-25 Category 2 98 0
Katrina Oct.28- Nov.1 Tropical Storm 40 0
Lenny Nov. 13-23 Category 4 155 0
BRADENTON - Wild winds whip across frothy waves, pushing to the west, twisting to the east, spinning a vortex across the vast watery expanse.

As the tropical storm chugs across the ocean, it gathers steam, fueling on pockets of sun-baked waters, muscling up to become a hurricane.

The immense storm staggers an unsteady line toward the states, a natural fury as apt to break off-course and head back out to sea as spin into the shoreline.

"There's an unpredictability to these things," said Jay Moyles, Manatee County's marine rescue chief. "We can never tell what they're going to do."

With the Thursday onset of the Atlantic's six-month hurricane season rolling into place, emergency officials have taken to the task of readying residents for the storms. That includes putting the word out on the tricky nature of forecasting the monsters' movements.

It starts with knowing the nature of the storms - what they need to form, what keeps them driving and what happens when weather patterns change.

Heat - and plenty of it - plays a major factor in hurricane formation, said Dan Bramer, a researcher with the University of Illinois Department of Atmospheric Scientists. Tropical storms need water temperatures of 80 degrees Fahrenheit or warmer to fuel their growth.

That comes in plentiful supply during the Florida summer, when the sun passes in a high arc near the equator, shining its intense rays on these water bodies. Water molecules soak up the heat energy until they reach their evaporation point, then drift up into the atmosphere.

Swirling air, the precursor to a tropical storm, twirls over the warm water and sucks in the water vapor. The water molecules cool, releasing their heat to the air.

The hot air then rushes up through the center of the burgeoning hurricane, creating a vacuum near the water's surface. Cooler air from outside the storm rushes into the void, pulling water vapor with it. That vapor cools, releases its heat, and the cycle continues.

Thus, researchers say, hurricanes form. Years of watching the monsters power to life has taught that lesson.

Similarly, by peering back into history, scientists try to predict how the beasts will bounce across the waters. They look at how similar-sized storms have reacted in the same area, given roughly the same type of weather patterns, and use that information to predict which way the current storm will roll.

"If you do it over time, you can develop a thing called the 'average tracking error,' " said Frank Lepore, a spokesman with the National Hurricane Center in Miami. "You draw a line on the water where the storm should go. We've done this enough, we've gotten the margin of error for that line down to about 100 miles for 24 hours of a storm's movement."

Just 30 years ago, he added, that margin of error hovered around 140 miles on either side of the storm line.

Still, surprises come.

"They are the experts," Laurie Feagans, Manatee County's emergency management chief, said of the NHC hurricane forecasters. "Despite all the technology, all the advances, forecasting where these things will go is still kind of a guessing game."

Last hurricane season provides ample evidence of the difficulty, with three prime examples standing out.

Hurricane Floyd, a storm nearly as strong and four times the size of Hurricane Andrew, which battered southeastern Florida in 1992, churned to life as a tropical storm on Sept. 7. Twirling off the northeastern coast of the South American continent, it began a track that carried it on a line for southern Florida.

For the next eight days, Floyd powered up and beat a steady path toward the Sunshine State. By Sept. 14, the storm sat just a couple hundred miles off the coast, with steady winds approaching 150 mph.

Florida's emergency management leaders began a steady evacuation along the state's eastern coast, looking to move people out of harm's way.

Then Floyd threw a curve. On Sept. 14, it curled to the northwest.

The evacuations followed it up the coast, with east-central Florida residents fleeing the approaching fury.

And Floyd twisted again, this time curling to the north between Sept. 14 and Sept. 15.

The evacuations once more followed it up the coast, with northeast Florida residents hitting the road.

And Floyd twisted again, eventually rolling back to the northeast for a hit in North Carolina, with sustained winds of about 100 mph. The storm retained enough fury, and pumped enough rain onto an already soggy state, to kill 57 people and cause roughly $6 billion in property damage.

Florida, spared a direct hit, still ended up with about 2.2 million residents and visitors on the highways, desperately seeking shelter and wondering whether they would journey onto the roads again for the next scare.

"That's our worst nightmare," said Lepore, the NHC spokesman, said Frank Lepore, "a situation where a storm recurves.

"We knew (with Floyd it was) going to make a turn, but the issue is how soon or how late? If it turns too late, then hurricane-force winds reach shore. If it turns too late, then the storm turns and runs parallel to coast, sort of weed-whacking its way up the coast."

Mother Nature, of course, didn't stop with Floyd.

Tropical Storm Harvey powered to life Sept. 19 in the eastern half of the Gulf of Mexico. The storm rolled off on an eastward path, bearing down on the Tampa Bay area.

Though it would not gain much strength over its relatively short, three-day life, it would confound forecasters nonetheless. The storm continued on a course for a direct hit on Tampa Bay for two days, then veered off in the early morning hours of Sept. 20.

Harvey took an abrupt right turn, clipping southward parallel to the Suncoast shoreline for a day before taking an equally abrupt left turn and smacking the Fort Myers area with its full force. The storm packed winds of less than 60 mph, but dropped a foot of rain in the area, causing $15 million in damage before dwindling out.

"That thing just kind of hovered off our coastline," Moyles said. "That was one of those calls that we made to stay on board. We saw it progressing toward us, and everybody thought it was going to shoot on by."

Perhaps the greatest proof of unpredictability came in the season's last storm, Hurricane Lenny, which rose in the Caribbean on Nov. 13 for a 10-day ride.

Where many storms surprise forecasters by darting this way and that, Lenny threw an immediate curve. It was the first tropical storm in the 100-plus years of national records that ever rolled solely from west to east, with a little zig and a mini zag here and there.

"That's the thing with these," Moyles said, "you just never know - never. The key is to be ready for anything. Get your hurricane plan together, know what you're going to do when a storm approaches, and you should never get caught off-guard, no matter how many times these things jump around."


Kevin Horan, environmental and legislative reporter, can be reached at 745-7037, or at khoran@bradenton.com




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