It was the most average of hurricane seasons, and the most unpredictable of hurricane seasons.
It started way early, with Subtropical Storm Andrea, which formed on May 9 (officially the season begins June 1). And now it is going to end way late, with Subtropical Storm Olga, currently in the Caribbean.
[A subtropical storm, incidentally, is a hybrid between a fully tropical system and a fully extratropical or midlatitude one. The U.S. National Hurricane Center has been naming subtropical storms since 2002.]
Olga is the first December named storm in the Atlantic since 2005's Hurricane Epsilon. As Jeff Masters points out, there have now been 17 named December Atlantic storms since record-keeping began. And Masters adds this tantalizing piece of information: "Seven of the 17 December storms have occurred since 1995." On a similar note, over at The New York Times, Andrew Revkin is also asking whether the 2007 season, with its abnormal length (if not its abnormal number of intense hurricanes), could be a hint that the climate's changing.
Well, here's what we can safely say about this: A number of scientists do indeed expect lengthening of the average tropical cyclone season as a result of global warming. Simply put, the tropical oceans ought to warm up enough to sustain hurricanes earlier in the year, and also ought to remain warm enough to sustain them later into the year.
This logic suggests that our traditional June/November Atlantic hurricane season bookends may indeed need to topple that is, provided that no countervailing changes occur as a result of global warming that have the effect of hemming the hurricane season back in again.
But of course, there are a lot of complexities here. For example, you will note that our earliest and latest named storms of 2007, Andrea and Olga, were both subtropical in nature. And as I mentioned previously, the National Hurricane Center didn't even start naming these types of storms until 2002. So I can already hear the argument from skeptics: The season isn't really getting any longer, it's just that now we're paying more notice to subtropical storms....
Maybe that's right. I, however, remain convinced that global warming is already changing hurricanes in myriad ways but that due to the complexity of the science and the general unpredictability of weather, it is exceedingly hard to detect the effect definitively at this point.
In any event, the 2007 Atlantic hurricane season continues to tantalize. In some sense, I'm going to be glad it's over (whenever it finally ends) just so it will stop thwarting, at every turn, my attempts to put it in a box and categorize it.
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