A term I hadn't heard before, but one that seems to be very significant. Hope Gustav hits a cold spot.

"That's kind of the scary part here," Shay said. "You look at this and say, 'Boy I hope this thing doesn't really explode,' but it probably will."

It happened in 2005. "Katrina went over the Loop Current and intensified rapidly," said Mark DeMaria, a Colorado-based expert on hurricane strength with the National Oceanic and Atmospheric Administration.

Then less than a month later a weak tropical storm named Rita followed Katrina into the Loop Current. Thirty hours later it was a Category 5 monster.