On hurricane seasons

May 1, 2006

When we flip the monthly calendar next, it will be the start of the Atlantic hurricane season.  In a fortnight, the (east) Pacific hurricane season will begin.

Each weekday this month, this blog will feature a hurricane related post, with each day having a broad theme.  Today the topic is the notion of a hurricane season.

The season is defined such that vast majority (95%+) of tropical activity falls within the given time period (beginning as described above, and ending on November 30 in both basins. 

Because of this definition out of season activity is rare by design.  This is especially true for the Pacific basin. The only out of season hurricanes in the 56 year record are Hurricane Alma of 1990 (which started to form on May 12), and Hurricane Winnie of 1983 (which existed from December 3-7). During the same span in the Atlantic, there were four such hurricanes and even more tropical and subtropical storms. The strongest of these was Hurricane Able of 1951, which strengthened to a category 3 just east of the Outer Banks of North Carolina on May 21.

As far as filling the season with activity goes, the Pacific basin is generally the more regular of the two as the Atlantic has a sharper peak in activity. There, seasons like the 1992 Atlantic one, in which the first hurricane started to form on August 16 and the season's activity ended on October 30 are very rare (but they do happen, in 1964 tropical storm activity was limited to the space between July 6 and September 9). Of course, short compressed seasons are no guarantee that there will not be much damage; that first hurricane of 1992 was none other than Andrew.

With regards activity destructive to the US, there is a bias towards the latter half of the season as the bulk of the costliest storms occurred between mid-August and the end of October. Two early exceptions to this, the June storms of Agnes (1972) and Allison (2001), were damaging not because of their winds but because of their moisture which caused extreme flooding.

Tomorrow's post will use the title of this blog as an eponym


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