Saturday, August 27, 2005

Gulf Loop Currents

Graphic courtesy of Texas A & M University

This morning, the New Orleans Times Picayune, in a front-page article by Mark Schleifstein, reports that Katrina now has "a path forecast to hit southeast Louisiana on Monday as a Category 4 storm with top winds of 132 mph."

He adds:
National Hurricane Center forecasters were predicting landfall in lower Plaquemines Parish.
Plaquemines Parish is a lightly populated, poorly developed lowland delta at the southern tip of Louisiana, built by eons of Yankee mud flowing down the Mississippi River. Obviously, though no one wishes harm to anyone, if the projection holds and Katrina makes landfall there, it would be one of the better of the bad scenarios imaginable.

Although it's still too early to be sure where Katrina will make landfall, this morning's NHC report titled Hurricane Katrina Strike Probabilities assigns a slightly higher chance to a landfall near New Orleans than to Pensacola.

The really interesting part of Schleifstein's article comes down the column, where he mines this quote from Lixion Avila, a forecaster for the National Hurricane Center:
Katrina is expected to pass over the "loop current," a doughnut-shaped circle of warm water that extends down 200 feet that has broken off the Gulf Stream and is floating in the Gulf.

In his 10 p.m. update, Avila described the movement over the current akin to "adding high octane fuel to the fire."

Such loop currents are believed to be capable of causing the intensity of a hurricane to jump as much as a category or two.

So Avila said he would not be surprised if Katrina reached Category 4 strength before going ashore.

"But we don't have good skills in predicting such changes in intensity," he said. "It could intensify rapidly or weaken rapidly right afterward, or right at landfall."
After the shock of the 1995 hurricane season, Pensacola Beach residents heard from a few experts who shared their fears that some sort of "channel" had been created in the Gulf which might explain why Hurricanes Erin and Opal both made a bee-line for Pensacola Beach. A number of preliminary storm reports by Florida meteorologal students mentioning that possibility also circulated briefly on the beach. It looks like one such report may be available from the American Meteorological Society, which also provides an on-line abstract.

The interaction of atmospheric, surface, and water currents is so complex few can claim the ability to understand all of their implications -- for now. But you have to wonder if those old rumors about Erin and Opal being steered our way by a "hurricane channel" had substance.

For those interested in learning more, apparently the Minerals Management Service has a more extensive report you can order. MMS is a U.S. Gulf of Mexico research center which, as Gulf drilling opponents know too well, devotes a substantial part of its resources to publicly advocating for the petroleum industry with reductio ad absurdum arguments like "oil drilling platforms make good houses for fish."

But their often hefty scientific reports are mind-numbingly thorough, scientific, and reality-based. No "faith based" work there. Not when money's on the line.

No comments: