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El Nino Has Calming Effect on Hurricane Season


Posted on 07 Aug 2009

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In recent weeks, forecasts for the return of El Nino - warmer than normal waters along the equatorial central and eastern Pacific Ocean - have come to fruition. NOAA's Climate Prediction Center, a division of the National Weather Service, now predicts a 50 percent probability of a near-normal season, a 40 percent probability of a below-normal season, and a 10 percent probability of an above-normal season. Forecasters say there is a 70 percent chance of seven to 11 named storms, of which three to six could become hurricanes, including one to two major hurricanes (category 3, 4 or 5).

The main change from the May outlook is an increased probability of a below-normal season, and an expectation of fewer named storms and hurricanes. The May outlook called for nine to 14 named storms, of which four to seven could become hurricanes, including one to three major hurricanes. During an average season, there are 11 named storms with winds of at least 39 mph, of which six become hurricanes with winds of 74 mph or greater and two of those become major hurricanes with winds of 111 mph or higher.

“El Niño continues to develop and is already affecting upper-level atmospheric pressure and winds across the global tropics,” said Gerry Bell, Ph.D., lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center. “El Nino produces stronger upper-level westerly winds over the Caribbean Sea and tropical Atlantic Ocean, which help to reduce hurricane activity by blowing away the tops of growing thunderstorm clouds that would normally lead to tropical storms.”

According to its August Atlantic hurricane season outlook, NOAA now expects a near- to below-normal Atlantic hurricane season, as the calming effects of El Niño continue to develop. But scientists say the season’s quiet start does not guarantee quiet times ahead. The season, which began June 1, is entering its historical peak period of August through October, when most storms form.

“While this hurricane season has gotten off to quiet start, it’s critical that the American people are prepared in case a hurricane strikes,” said Commerce Secretary Gary Locke. El Niño may mean fewer storms compared to recent seasons, but it doesn’t mean you can let your guard down,” said Jack Hayes, Ph.D., director of NOAA’s National Weather Service. “History shows that hurricanes can strike during an El Niño.” Some examples include Betsy in 1965, Camille in 1969, Bob in 1991, Danny in 1997 and Lili in 2002.