Advocate staff photo by ARTHUR D. LAUCK

LSU Earth Scan Lab Director Nan Walker uses satellite images like this one to study the Gulf of Mexico. This image shows the current water surface temperatures in the Gulf.

Hurricane Dennis managed to cool the eastern Gulf of Mexico to a level that might not maintain another tropical storm. But the middle of the Gulf of Mexico is still nice and warm, thanks to a loop current that comes from the Yucatan Channel up toward Louisiana and then back out the Florida Straits.

It is part of the Gulf Stream.

If Hurricane Emily maintains course to eastern Mexico or south Texas, as predicted by the National Hurricane Center, it will find more warm water to strengthen it after it crosses the Yucatan Peninsula.

Dennis cooled the waters off the western shore of Florida. But all year long, the "loop current" keeps the Gulf waters south of Louisiana nice and warm. And that warm water is part of what can beef up a hurricane or tropical storm from a strong breeze to a beach-wrecker, according to Nan Walker, director of the Earth Scan Lab at LSU.

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Walker uses satellite imagery to study the Gulf of Mexico and other parts of the ocean -- tools unavailable until just the past few decades. One of the images captured from satellite data and used by the lab is a heat image of the Gulf of Mexico.

When one looks at a water temperature image from the satellite, there's plenty of yellow and orange -- the signal for warm water -- in the central and western Gulf of Mexico, along with the Caribbean Sea, where Emily is churning. Dennis traveled through the Caribbean, crossed Cuba, and slammed Sunday into the Pensacola-Navarre Beach area of Florida.

Where Dennis tracked along Florida, the colors on the image are more blue, signaling cooler waters.

This week, imagery shows that the waters along Florida were 26 degrees Celsius (78.8 degrees Fahrenheit), which is too cool to maintain a hurricane.

"That doesn't mean it would die," Walker said, but there would be no real "fuel" to strengthen it and keep it going.

But out in the middle of the Gulf of Mexico, where the loop current comes up from the Caribbean Sea, the waters are 29 degrees Celsius (84.2 degrees Fahrenheit) and in the western Gulf of Mexico, it is 30 degrees Celsius (86 degrees Fahrenheit).

"The biggest source of heat is in the middle" with the loop current just about 75 miles south of the mouth of the Mississippi River, Walker said.

Hurricanes and tropical storms are fueled by the warmth in the oceans. But hot water is just part of the equation in tropical weather. What is happening in the atmosphere is also part of the mix.

Walker said the ocean's part in what makes hurricanes work is not as well understood, and that is one reason she's doing research on what happens in the water when tropical weather passes.

Right now, the level of knowledge may not be high enough to help predict what will happen, but it is good enough to explain what happened after the fact, she said.

For example, Hurricane Ivan really smashed the Alabama and Florida coasts -- the same places pretty much hit by Dennis on Sunday. But perhaps it could have done more destruction, Walker said.

But sometimes strong storms like Ivan have such a low internal pressure, they tend to cause cold water from the depths to come to the surface, which actually weakens storms. Ivan caused some cold water upwelling and lost some wind speed, Walker said.

Hurricane Lili is another example of how water -- and air -- can interact.

Most Louisianans will remember the two storms that plagued Louisiana back-to-back in 2002 -- first Tropical Storm Isidore, which hit eastern Louisiana, and Hurricane Lili, which came ashore in Vermilion Parish.

Isidore hit the Yucatan Peninsula and then headed north to Louisiana. A week later, Lili was taking a similar path. Most people went to bed fearing early morning arrival of a Category 4 hurricane that was predicted to flood as far inland as New Iberia. Instead, a Category 2 hurricane, which still did a lot of damage, arrived on the shoreline. The predicted catastrophe -- which included the possibility of many deaths -- fizzled to a certain degree

Walker and fellow School of Oceanography and Coastal Science researcher H.A. Hsu studied what happened to Lili using satellite data.

Hsu discovered Lili sucked some dry air in from the west of Louisiana, which helped weaken it.

Walker found Lili hit water that had been cooled the week before by Isidore and, as it was late in the season, it had not warmed back up in the interval (which will likely happen in the eastern Gulf).

Every six to 13 months, the loop breaks off from the current and becomes a "ring current" and drifts to the west. This phenomenon can affect weather as well as create problems for oil exploration and production off western Louisiana and Texas, Walker said.

She is studying cool water up-welling that is caused by the loop current creating "cyclones" in the water, or counter-clockwise current that brings cold water to the surface and how those interactions affect currents and weather, like tropical storms.

The more scientists find out about how sea surface temperatures work, Walker said she thinks that forecasters, such as those at the National Hurricane Center, will be able to make better predictions of storm intensity, which lags behind the ability to predict the path.

While the ocean temperatures come from a geostationary satellite, GOES-12, the Earth Scan Lab has a wide variety of other tools it uses as well to do remote sensing for research purposes.

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