Tropical Cyclone Activity at 30 year low
Posted by 1969 on 10/30/2009, 11:10 pm
Ryan N. Maue's Seasonal Tropical Cyclone Activity Update
http://www.coaps.fsu.edu/~maue/tropical/

Oct 29: The North Atlantic hurricane season has not produced a storm in over 3-weeks and, if no more develop, the season overall would rank as the slowest since the El Nino year of 1997. Hurricanes Bill and Fred accounted for over 82% of the Accumulated Cyclone Energy [ACE**] -- a metric that combines intensity, duration, and frequency of hurricanes and tropical storms during a year. The remaining storms were weak, rather short-lived and unremarkable. Indeed, the Accumulated Cyclone Energy [ACE] of 44 ranks among the slowest during the past half-century.




Elsewhere, the Northern Hemisphere and Global ACE when calculated either with 12- or 24-month running sums, remains just above historical 30-year lows. Indeed, the global ACE sunk to record low levels during the early summer prior to the typhoon activity in the Western Pacific and the hurricane activity in the Eastern Pacific. While it may seem like the world has experienced considerable tropical cyclone activity lately, 2009 as a whole is still well behind normal or climatology. The previous Southern Hemisphere cyclone season including the Southern Indian and Pacific Oceans along with the Australian region produced historically low levels of ACE (from Oct 2008 - Apr 2009). So a global sum during the past 12 or 24 months will simply show the depressed tropical cyclone activity experienced.

http://www.coaps.fsu.edu/~maue/tropical/global_year_ace.jpg

This is a natural consequence of the rather unusual flip from strong La Nina to El Nino conditions during the past calendar year, which did not happen at all during the period of 1976-2006 as indicated by the MEI-ENSO INDEX (LINK). It is expected by NOAA and others that the current-El Nino is locked in for the rest of winter 2009-2010 and may indeed strengthen. This would suggest enhanced typhoon activity in the Western Pacific throughout the rest of the fall and winter which will necessarily increase the NH ACE. The Southern Hemisphere TC season may begin at any time now, but most activity is experienced between January and March.
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Tropical Cyclone Activity at 30 year low - 1969, 10/30/2009, 11:10 pm
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