The reason, from my point of view, is a multiple of variables that came together this year with such crushing force, in a "perfect storm" of hostile conditions. 2009 is the counter to 2005.
In 2005, we saw hot SSTs, little to no shear over much of the basin, moderate easterly flow (not too fast or too slow), steady high pressure over the oceans (Azores and Bermuda), very moist upper atmosphere. I don't know what the statistical odds of this occurring were or are, or when this happen again, but it did occur.
Likewise, 2009 has seen fierce, not only easterlies, but westerlies, and heavy shear from both directions; very powerful troughs and fronts pushing very far south across the U.S. and into the Atlantic; dry air, which is spread out, but not plentiful; highs (Azores and Bermuda) which have been very broad and far reaching at times, creating a lot subsidence, and at times weak enough to allow quick northerly escape routes for any viable waves exiting Africa; average to below average SSTs; and ULLs, again spread out, but not plentiful.
The statistical odds against this all coming together have to be just as astronomical as 2005's odds against it occurring all at once.
To be at September 6, with 5 named storms, and only 1 hurricane, albeit a major one, does not by itself stand out, however, when shown against the backdrop of the season's conditions as a whole, we know that, with similar conditions persisting and the season at halfway, this might be it in terms of landfalling systems.
One key reason, fall to late fall conditions have been setting up with polar lows reaching the U.S. with quite a punch recently, and lined up to do so for the foreseeable future.
One caveat to the odds, is that very quiet seasons and very active seasons have occurred more than once that we can show.
Active: 1887, 1933, 1969, 1995, 2005
Quiet: 1965, 1977, 1982, 1986
Either the odds aren't as great for or against a 2005, or 2009, or wild fluctuations are the norm from year to year.
I think the latter is true. I think you can line up a 2005 right next to a 2009 in the same decade of seasons, if one wanted to, and the likelihood that this could occur would favor you. |