click for current data

From the south, the Gulf Stream carries warm water into the Gulf of Mexico past the Yucatan Peninsula from which it flows west and then out of the Gulf through the Florida Straits. Normally flowing directly northeast from Cozumel, past Cuba's northern coast, it sometimes bows northward into the Gulf. The bow has been named the Loop Current.

At one extreme, warm water has an almost direct path to the Florida Current. The friction of the moving current against the still water of the Gulf sets up a quasi-permanent clockwise recirculation known as the Cuban Vortex. When the Cuban vortex is active, much of the heat carried by the Gulf Stream bypasses the Gulf of Mexico and is carried away to the north. Surface water temperatures stay relatively low and storm intensification is inhibited.

At the other extreme, the Loop Current intrudes into the Gulf of Mexico, forming an intense clockwise flow. Occasionally this loop will reach as high as the Mississippi river delta or the Florida continental shelf . In this configuration of the Loop, water temperatures in the Gulf skyrocket and storms are fed to maximum intensity.

Naval labs data now shows the Loop Current periodically (6-11 month cycle) breaks off a clockwise spinning self contained eddy loop. Typically breaking off south of Florida the eddy drifts westward and weakens over a period of months. The eddy is full of warm water. An eddy was active south of Louisiana in August 2005 contributing to the strength of both Hurricanes Katrina and Rita. Check out current conditions at the Naval Labs website.

Conclusion: Confluence of a Loop Current Eddy (heat source) and La Niña (less shear in the atmosphere) conditions in August and September contribute to the formation of the storms most dangerous to New Orleans. If they occur during a peak of the Atlantic Multi-Decadal Oscillation and during a period of global warming, watch out!

It looks like April 2007 may see formation of a new eddy.  This is a little early and may be good news. If  La Niña emerges in the Pacific as some forecasters are now expecting, the 2007 hurricane season could be active.

Hot water near the surface of the ocean can fuel tropical storms and hurricanes. In 2005 Hurricanes Katrina and Rita passed over an oceanic anomaly that scientists have taken to calling the Loop Current. This meandering column of Gulf Stream water can be nearly 80 degrees Fahrenheit and can extend as deep as 300 feet below the ocean's surface -- providing nearly limitless fuel and preventing cold-water upwellings. This in turn, can allow a storm to grow from merely damaging to truly cataclysmic in the span of a day.

According to experts at the National Science Foundation, the warm, clear Gulf Stream waters that flow through the Gulf of Mexico tend to get diverted as they pass from the Yucatan Peninsula up toward Cuba. This creates a horseshoe-shaped column of water up to 100 times as large as the Amazon River that flows into the Gulf of Mexico before either passing out between the Florida Keys or becoming a circular eddy current that cuts off from the Stream and can linger in the Gulf for months before finally cooling down. In 1999, Nick Shay, a scientist at the University of Miami, identified this loop current and its accompanying 330-foot-deep "warm core rings" as the energy source likely to cause a hurricane to grow from a Category One to a Five so quickly. "This is the heat," Shay said. "This is the energy source. It's like a big fuel injector in the middle of the ocean."