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When storms get bad, blame the Loop Current

The warm water in the Loop goes deeper than elsewhere in the gulf; the heat feeds the storms.

By JEAN HELLER
Published June 13, 2006


Compared with storms of the past two years, Alberto looked tame, a ragged and disorganized tropical storm that promised some flooding but also much-needed rain.

Then, like a bully stepping over a line drawn in the dust, Alberto crossed a Gulf of Mexico phenomenon called the Loop Current. And just that quickly, forecasters predicted that the first named storm of the 2006 season likely would become a hurricane before making landfall early today along Florida's Big Bend.

While the Loop Current isn't a household name, meteorologists know the river of warm water can have a profound and sometimes catastrophic effect on summer weather.

And it isn't always predictable.

Hurricane Katrina, which devastated Mississippi and Louisiana last summer, also was energized by the Loop Current, which forms as a warm Caribbean current enters the Gulf of Mexico, makes a U-turn and exits the gulf around Florida's southern tip.

The exact location and configuration of the loop varies.

Though still disorganized and pummeled by wind shear, Tropical Storm Alberto nonetheless gained enough additional strength as it crossed the Loop Current that National Hurricane Center forecasters declared late Monday it could strengthen into a minimal hurricane.

Did the effect of the Loop Current catch forecasters by surprise?

"We knew it was there," said Richard Pasch, a specialist at the hurricane center. "We just didn't know what its impact would be."

While warm water is the source of the energy that creates and sustains all tropical storms, the warm water in the Loop Current has a more profound impact.

"The rest of the gulf water is about 81 degrees now to a depth of about 150 feet," Pasch said. "When a storm goes across the water, it churns it up, and the cooler water below comes to the surface, so the storm can't develop.

"But in the (Loop Current), the warm water goes down 250 to 300 feet, so when it gets churned up, more warm water upwells and feeds the storm."

Robert Leben, an associate research professor at the Colorado University Center for Astrodynamics Research in Boulder, saw the same thing happen last summer on a much more horrific scale.

Katrina evolved from a Category 3 to a Category 5 hurricane in just nine hours as it passed over the Loop Current, Leben said.

"A hurricane is like a steam engine," Leben said. "The more heat that is put into it, the faster it is going to run."

When Katrina passed over it, satellite readings showed water from the Loop Current was 20 to 30 inches higher than surrounding water, Leben said, noting a tight correlation between sea-surface height and the temperature beneath the surface.

Normally, the Loop Current makes a U-turn about midway up into the gulf before taking a southeasterly track toward the Florida Keys. It can, however, go as far north as the Mississippi Delta, as it did last summer, or as far east as the continental shelf off Florida's Gulf Coast, where it is now, Leben said.

While it carries different names depending on its location, the Caribbean Current, which flows north toward the Gulf, the Yucatan Current, the Loop Current, the Florida Current and the Gulf Stream are all the same system, formed by the rotation of the Earth.

"It starts deep in the Caribbean and winds up in England," Leben said. "Pretty amazing, really."

[Last modified June 13, 2006, 08:31:18]


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