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WSI: El Nino Calming Hurricane Predictions

A new El Nino event -- warming of surface temperatures in the eastern equatorial Pacific ocean -- combined with cooler Atlantic ocean temperatures is likely to make the 2009 Atlantic hurricane season "relatively quiet," Andover, MA-based WSI Corp. said Monday.

WSI, which previously called for a total of 11 named storms, including six hurricanes, with two of them intense (Category Three or greater) forming by Nov. 30 (see Daily GPI, May 27), said it is sticking to that forecast.

"Ocean temperatures in the tropical Atlantic are cooler, relative to normal, than at any time since 1994," said WSI seasonal forecaster Todd Crawford. "Further, the new El Nino event continues to strengthen, and the recent patterns of tropical Pacific thunderstorm development have already responded to El Nino. This has resulted in an unfavorable wind shear environment across the tropical Pacific. This early emergence of this enhanced wind shear along with the relatively cool tropical Atlantic temperatures will almost certainly result in a less-active season then last year, and could potentially result in an unusually quiet season."

The number of tropical storms forecast by WSI would be fewer than occurred during the 2008 season, when a total of 16 named storms, including eight hurricanes, five of them intense, formed in the Atlantic. But it would be about the same as an average hurricane season, which has 11 named storms, including two major hurricanes, according to the National Oceanic and Atmospheric Administration (NOAA).

In its initial hurricane forecast for the 2009 season WSI had predicted 13 named storms, three of them intense (see Daily GPI, Dec. 29, 2008). But a continuation of relatively cool tropical Atlantic Ocean temperatures, combined with the waning of a recent La Nina event -- unusually cold temperatures in the eastern equatorial Pacific -- and normal to above-normal wind shear in the tropical Atlantic, prompted the forecaster to reduce those numbers in April (see Daily GPI, April 23).

Other forecasters calling for a relatively mild hurricane season include Colorado State University (see Daily GPI, June 3), NOAA (see Daily GPI, May 22) and AccuWeather.com Chief Long Range Forecaster Joe Bastardi (see Daily GPI, May 15).

Last week the UK-based Meteorological Office said it expects only six tropical storms to occur in the North Atlantic between July and November, well below the long-term average of 12.4 (see Daily GPI, June 22). There were 15 North Atlantic storms during the 2008 hurricane season.

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