Dean and Felix - Deja vu all over again

As Weatherwoof recently posted about his fascination with hurricanes, I will follow up with a fetish about how entrenched weather patterns may be one year and then be replaced by a new pattern (or more commonly, none at all) the next year.

Dean and Felix are showing how short term fixing in weather features can have disastrous consequences for those who live in the way of the storms that are controlled/steered by these patterns. Hurricane Dean and Felix are the latest examples of this. They have followed a very similar path and fate as they churned across the Caribbean basin and explode into major hurricanes south of Jamaica and make landfall in roughly similar places. Belize, normally a quiet place with respect to tropical storms, is getting rocked this year by two huge storms within a few weeks. The same features that produced the heavy rains in Iowa also are pushing these hurricanes along a more southern trajectory and blocking their entry into the Gulf of Mexico.

Two years ago, a fixed pattern allowed Rita and Katrina to exhibit similar behaviors. The year before that it was Jeanne and Frances on the east coast of Florida. Like Belize, the east coast of Florida usually watches the hurricanes pass to the east.

While there are prevailing patterns that repeat year to year - one such pattern is the June hurricanes that form in the Gulf and go inland across the Piedmont of Georgia and the Carolinas, and another such pattern are the Cape Verde storms that take 2 weeks to move from Africa and move up the East Coast hitting NC or New England - in individual years, some unique temporal patterns pop up.

While the popular press make a fair amount of noise about climate change and the effects resulting in more intense and damaging storms, it would be interesting to note some things:

1. The largest storm, in terms of shear area, that has been observed in the Atlantic was Hurricane Dog in 1950 - it did not make landfall but passed near Nantucket.
2. The most dangerous storm in America occured in Galveston at the turn of the previous century killing thousands.
3. The lowest pressure recorded was Wilma in 2004 which just beat Gilbert in 1988 which, in turn, just beat the 1938 Labor Day hurricane in the Keys. Many storms now are being monitored several times a day by hurricane hunters (starting in earnest in the 1980s) and this would suggest that previous storms, if measured in a similar fashion, may have had similar drops in pressure in remote areas. These data were not captured due purely to unadvanced detection methods. The 1935 hurricane minimum pressure stood for 50+ years as a record, before falling to Gilbert (which destroyed Cancun with a direct hit).
4. While category 5 hurricanes (top of the Saffir-Simpson scale) can develop in any given year, the striking of land at Cat 5 is rare - particularly in America. The 1935 hurricane, Camille in 1968 and Andrew (borderline Cat 5) in 1992 are the rare cases of landfall at peak intensity. Recently, Ivan, Katrina, and Wilma were all monster storms which weakened prior to landfall. Had the levees held in New Orleans, Katrina would have been relegated to local lore - much like Fran in NC in 1997, Hugo passing directly over Charleston in 1989, Allen in Texas in 1980, Betsy in New Orleans in 1965, and so on.
5. Frequency is so variable as to defy prediction. While 2004 and 2005 were rather active years - 2006 was uneventful. Until August, 2007 was likewise uneventful. Hurricanes, which run in cycles like sunspots, are not good barometers of the effects of climate change. One is better off sticking to glaciers in the Alps or ice on the Arctic as they are relatively static and easier to monitor.