September 21, 2005

Rita is the 17th named storm of the Atlantic hurricane season, making this the fourth-busiest season since record-keeping started in 1851. The record is 21 tropical storms in 1933: more than that (and it is quite likely, this year), and we begin the list anew with the Greek alphabet. So far, the Atlantic record is 12 hurricanes in a single season (1969), or six intense hurricanes (1996). Globally, the record is 106 tropical storms, with 64 hurricanes. Six separate hurricanes have hit Florida in the last 13 months.

We are going to see records shatter, this year.

Part of this is that, this year, we are just descending into the most active part of a multidecade hurricane cycle. Part of it is also that this year, the waters of the Gulf of Mexico have been warmed by the flow off a particularly early Bermuda high: leading to a flirting-with-record summer (10th warmest on record overall) and to waters between 29 and 33 degrees Celsius, reaching down to depths well below the 75 metres churned up by low grade hurricanes and tropical storms. In fact, the function of hurricanes within the terrasphere is to redistribute some of that excess heat energy away from the tropics.

Up until two years ago, Typhoon Tip and Hurricane Gilbert were the two most intense storms ever, as measured by central air pressure (870 and 888 millibars respectively); Typhoon Forrest and Gilbert were the two most quickly intensifying storms (from 976 to 876, and from 960 to 888 mb respectively). Tip also holds the record as the largest tropical storm yet, with tropical storm force winds that extended 1100 km from its centre. (Ask Darwin what size means though to localised destructive capacity: Tracy's winds only extended 50 km from its centre when it struck on Christmas Eve, making it the smallest ever.)

Of the deadliest ever Atlantic storms which could have a specific month assigned to them (as compiled by the National Hurricane Center to 1997, several later storms not yet included), 40% occurred in September, 30% in August, and 20% in October. September is also the single deadliest hurricane month, with 40% of all hurricane-related deaths, followed by October with 30%. In fact, the first seven hurricanes on the list all occurred in either September or October. These numbers might be skewed by increased vulnerability of buildings already damaged by hurricanes earlier in the season.

The hurricane season is not over until November 30.

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