Hurricane Lili fizzled, but still left residents' nerves frayed Rapid reversal in intensity of storm is unexplained

10/04/02 By Mark Schleifstein
Staff writer/The Times-Picayune
Why did Lili suddenly collapse from a 145-mph Category 4 hurricane to a 90-mph storm on the Louisiana coast Thursday? Was it simply a reversal of the forces that had caused the storm to explode from a 90-mph Category 1 on Monday to a monster storm on Wednesday? Or was it something else?

"There will be many explanations after the fact, and perhaps many Ph.D. dissertations," National Hurricane Center hurricane specialist Lixion Avila said as Lili blew ashore on the central Louisiana coastline. "The truth is that nobody was able to predict these sudden changes in intensity."

Trying to predict a storm's strengthening remains a frightening concept, Avila said. "I'm so happy that it . . . weakened before it reached the coast," he said. "The other way around could happen at any time with another hurricane, and that scares me."

A storm that suddenly strengthens before landfall could threaten the lives of thousands of people caught unaware in their homes or trapped on highways trying to make a last-minute dash for safety. An accurate forecast literally can be a matter of life and death.

But even those in the business of making such predictions are quick to say that hurricane researchers are only beginning to understand the many pieces of the intensification puzzle.

"I think my batting average in such predictions is good -- .300," said John Kaplan, a meteorologist at the National Oceanic and Atmospheric Administration's Hurricane Research Division in Miami who is studying rapid intensification. "But the public wouldn't be satisfied with that sort of prediction record."

Landfall forecast accurate

Understanding how hurricanes gain strength and translating that knowledge into computer models that help forecasters predict what specific storms will do, Kaplan said, has been much harder than even predicting where they will go. Forecasters, in fact, were remarkably accurate in predicting Lili's path through the Gulf of Mexico, but were caught off-guard by how quickly it strengthened before it began to weaken.

"During the past five years, we've improved our intensification forecasts by about 15 percent," Kaplan said. "But in the previous 20 years, there was no improvement."

That's because there are so many variables that influence a hurricane's strength: water temperature, wind shear, interaction with land masses, and some that aren't yet known.

Storms such as Lili provide researchers with opportunities to answer some of those questions.

Like many nascent tropical systems, Lili first had to develop an infrastructure in which to grow. The key is an inner core, often referred to as the hurricane eye, around which towering thunderstorms grow and begin to spin.

Lili had such a structure when it moved over deep, warm water surrounding Cuba and into the Gulf of Mexico.

At that time, some forecasters thought that Lili might have a hard time intensifying because the Gulf had been cooled a week before by the passing of Isidore, which mixed the warm shallow surface waters with the cooler water below. But the speed with which the steering currents moved Lili northwest toward Louisiana might have allowed the storm to overcome the cooling effect that usually saps a storm's strength, Kaplan said.

As Lili entered the Gulf, an upper-level low pressure system was already to the west. Kaplan said the counterclockwise winds around that system might have squeezed the thunderclouds surrounding Lili's eye ever tighter, which might have been a significant cause of its rapid intensification.

A steady supply of humid air in the central Gulf of Mexico also provided fuel for thunderstorms.

Unexplained influences

There may also be forces not yet discovered that helped Lili strengthen, Kaplan said.

As Lili approached Vermilion Bay on Louisiana's coastline, something caused the storm to lose its oomph, just in time to save New Iberia, Franklin and Morgan City from the disastrous effects of what National Hurricane Center Director Max Mayfield said was the largest hurricane to approach the Gulf Coast in a generation.

Kaplan said the cause was probably another combination of complicated forces.

The wind shear created by the same upper-level low that strengthened Lili may have begun tearing apart the storm's clouds. The low may also have begun pumping dry air into the system from the northwest.

Isidore's effects may also have played a role. Just a week before, it poured 10 to 25 inches of rain onto the shoreline, and much of that water ran into the Gulf, adding to the cooling caused by Isidore's winds.

Finally, Lili's inner core may have self-destructed. Hurricanes often form a second circular wind band around their eye that accordions in and out and eventually replaces the original eye. As Lili approached the coastline, both radar and satellite views indicated that something was pulling the storm's eye apart.

As plausible as the combination sounds, Kaplan said, storms with similar characteristics have continued to strengthen as they moved over much colder water before going ashore in Canada's Maritime Provinces.  . Mark Schleifstein can be reached at mschleifstein@timespicayune.com or (504) 826-3327.