Published on 20-Nov-09

Nov. 20, 2009 -- The 2009 hurricane season had activity at below-average levels. Our June and August forecasts correctly predicted below-average hurricane activity due to the development of a moderate El Niño. We consider this season’s forecasts to have been successful.

Nov 20, 2009 -- A forecast was initially issued for the 2009 season on 10 December 2008 with updates on 9 April, 2 June, and 4 August of this year. These seasonal forecasts also contained estimates of the probability of U.S. hurricane landfall during 2009. For the first time this year, probabilities of hurricane landfall were also provided for the Caribbean and Central America. The skill of our early June and early August forecasts was reasonably good, while our earlier predictions of early December 2008 and early April of this year over-estimated this year’s tropical cyclone activity because of our inability to judge the formation of the moderate El Niño event which began to develop late this spring.

During the August-October period, we also issued 15-day forecasts. These forecasts were primarily based on predicted activity by the global forecast models and the phase of the Madden-Julian Oscillation. These forecasts showed modest skill and will be refined and issued again during the 2010 hurricane season.

Activity in 2009 was reduced considerably due largely to the moderate El Niño event that developed. This event generated significantly stronger-than-average vertical wind shear, especially in the Caribbean and Gulf of Mexico. Consequently, only nine named storms, three hurricanes and two major hurricanes formed in 2009. This activity was 61%, 38%, and 51% of the 1995-2008 average activity for named storms, hurricanes and major hurricanes, respectively.

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