Hurricane Lili's Sudden Demise Probed

As Hurricane Lili churned toward landfall on the night of Oct. 4, she had racheted up from a Category 2 to a Category 4 storm, and there was real concern that she might go all the way to a Category 5.

In the labs of LSU's Hurricane Center, state meteorologist Jay Grymes, oceanographer Greg Stone and others were intently watching the storm, tracking it through the center's instruments and supplying advice to state emergency officials in preparation for the big hit.

"This was a system that was ready to strengthen," Grymes said. "It had all the factors in its favor. It took on a nearly perfectly symmetrical shape, which is representative of big storms."

Suddenly and against all expectations, Lili dropped down to a Category 2 storm about four hours before making landfall. It was a considerably weaker hurricane that dragged a storm surge across the marshes of South Louisiana and blew through Kaplan and Abbeville than anyone expected, confounding all the predictions and the hurricane models.

Hurricane models are no good if they can't predict how the storm will behave, so Lili's sudden drop in intensity generated a lot of interest.

"One idea was that Lili came over cool water that (tropical storm) Isidore churned up, but Greg's data showed otherwise," Grymes said. Lili passed right over one of the instruments in Stone's Wave-Current Surge Information System, one of a series of instruments that measures water temperature, wave height, direction and current speed.

WAVCIS was developed very much for the purpose of detecting storms while they are still far away from land, and gathering real-time data from them. WAVCIS showed that the water temperature had indeed cooled because of Isidore, but had bounced back by the time Lili came through a week later. Researchers had to look elsewhere to find the cause of Lili's slowdown.

Grymes has developed another idea about the cause. "A powerful storm is always symmetrical," he said, indicating a satellite image of Lili which showed a near-oval shape. "When Lili went from a two to a four, she was very symmetrical. But an upper-level low on her western flank began to shear off the western edge of the storm. This slowed the winds and perhaps also dried some of the moist air.

"This may not have been an unprecedented weakening, but in the 12-hour window preceding it we thought we were looking at the next devastating tropical storm to hit Louisiana since Andrew."

Storm prediction has always been more of an art than a science, but systems such as WAVCIS and the Earth Scan Laboratory at LSU are providing data to make it more reliable. WAVCIS showed that Isidore generated 25-foot waves and Lili generated 45 foot waves. Nevertheless, the waves from Isidore, which was only a tropical storm when it hit, caused more erosion.

That was partly due to the fact that Isidore was a slower-moving storm, enabling waves to beat the shoreline for a longer time. Where the two storms came ashore also made a difference. The water was shallower and muddier where Lili came ashore, and mud in the water absorbs a lot of wave energy.

"The bottom near Abbeville and Intercoastal City (where Lili came ashore) is gelatinous and soupy -- like yogurt," Stone said. "Fishermen have known for years that mud in the water has a damping effect. If Lili had followed the path of Isidore, the storm surge would have been much worse."

It is data like this, taken from real storms, that will help make the computer models more accurate. Plugging this data into existing models and seeing how far those model predictions deviate from the actual path and intensity of the storm will help give researchers the ability to tweak the models and make them more accurate. Both the Federal Emergency Management Administration and the Department of Naval Research have made funding available for LSU researchers to develop better storm models.

Commenting on the 2002 hurricane season, Grymes said, "I've never known two storms to hit Louisiana in such close succession. We had a decade of tropical storms in a week."

It is on just these occasions that LSU's Hurricane Center shows how valuable it is to the well-being of the state. With its real-time storm data and advisory capacity to the state Office of Emergency Preparedness, decisions can be made on road closings, evacuation routes, resource allocation and other procedures that can save hundreds, possibly thousands, of lives.

"We're taking science out of the classroom and applying it to the real world," Grymes said. "WAVCIS, Earth Scan, the Hurricane Center -- they were very active in making use of LSU resources for the benefit of the state."