The Gulf and Carribean seem to be ripe breeding grounds for especially vicious hurricanes this year. I have a hypothesis as to why.
Hurricanes are bred by the prevailing westerly winds in the mid-tropics, in combination with tropical heat and moisture. Recent Gulf hurricanes have been particularly strong, reaching Category 4-5 status, and reaching that staatus very quickly. I believe this is becauswe there is more warm, tropical water for hurricanes to breed over. The amount of tropical heat available to create Category 4-5 hurricanes is, in my mind, increasing sharply due to global warming. Here's why.
The Gulf and Carribean lose a significant amount of heat each year throught the action of the Gulf Stream, that northerly flow of warm water from the Carribean, along the Eatern Seaboard of the U.S., and past Newfoundland. It's driven by the sinking of massive amounts of very cold, salt-laden, dense water in the Northern Atlantic. As seawater freezes to create the polar ice caps, the seawater there becomes more dense, and sinks - all the way to the bottom of the ocean, where it begins to flow southward. This deep southward flow causes the upper-level northward flow we know as the Gulf Stream.
Oceanographers had identified as many as eleven giant columns of dense, salty polar water that ultimately drive the Gulf Stream. Last year, however, they identified only two - and those were significantly weaker than in previous years. The number of salty water columns has been decreasing because the polar ice caps are melting, making the polar seawater less dense. Less dense water doesn't sink to the bottom of the ocean, and can't drive the Gulf Stream.
As the Gulf Stream slows, the amount of heat being carried away from the Gulf and Carribean lessens, and tropical waters become relatively warmer. Warmer tropical waters mean more fuel for hurricanes, especially Category 4-5 monsters like Katrina, Rita - and now Wilma.
If the trend towards the melting of the polar ice caps continues, and it will, given global warming, we may, in our lifetimes, see the cessation of the Gulf Stream altogether. As this happens, expect even more, and more powerful, huricanes along the Gulf and East coasts for years to come.