U.S. Forecaster Lowers Atlantic Hurricane Prediction

April 7, 2009

Citing cooler seas and the prospect of a weak El Nino, Colorado State University’s hurricane team lowered its 2009 Atlantic forecast Tuesday to 12 tropical storms, of which six could become hurricanes.

The research team, founded by storm forecasting pioneer William Gray, said the season could see two “major” hurricanes of Category 3 or higher on the five-step Saffir-Simpson intensity scale. Hurricanes of that magnitude have sustained winds of more than 110 miles per hour.

In its December forecast, the CSU team predicted 14 storms, seven hurricanes and three major hurricanes in the 2009 season, which begins on June 1 and lasts six months.

The researchers said sea surface temperatures in the tropical Atlantic Ocean had cooled in recent months. Hurricanes draw energy from warm sea water, so cooler water could diminish hurricane activity.

In addition, the eastern Pacific Ocean could see the current weak La Nina conditions change to neutral, or even weak El Nino, by June, the researchers said. El Nino is a warm water phenomenon that can suppress Atlantic hurricane formation.

“If El Nino conditions develop for this year’s hurricane season, it would tend to increase levels of vertical wind shear and decrease levels of Atlantic hurricane activity,” Gray said.

Bill Read, director of the U.S. National Hurricane Center, downplayed the impact of El Nino, noting there have been active hurricane seasons during similar phases of the El Nino cycle. But he said cooler water could have an influence.

“Some of my forecasters have pointed out to me that the tropical Atlantic waters at this time of the year this year are somewhat cooler than the last several seasons,” he said in an interview with Reuters at the National Hurricane Conference in Austin, Texas. “If that continues that may be a more important factor on this season.”

While disaster management experts say long-range hurricane forecasting helps raise public awareness, many note it is an inexact science. Some forecasters, including the Colorado State team, have been well off target in recent years.

Colorado State predicted 15 tropical storms for the 2005 season, but a record 28 formed.

“You’re talking trying to discern weather events from a climate-type forecast. Therein lies a huge difficulty right there,” Read said. “That science is still in its infancy.”

Forecasts Closely Watched

The forecasts are closely watched by energy, commodities and insurance markets, particularly since the devastating 2005 season, when a series of hurricanes rolled through Gulf of Mexico oil and gas fields and Hurricane Katrina, the costliest in U.S. history, swamped New Orleans.

Colorado State predicted a 31 percent chance that a major hurricane would hit the U.S. Gulf coast this year, compared to a 30 percent long-term average. For the U.S. East Coast, the probability was 32 percent, compared to 31 percent long-term.

The 2008 Atlantic season was one of the busiest on record, with 16 tropical storms, of which eight became hurricanes. Five were of Category 3 or higher.

Cuba bore the brunt of last season’s destructive storms. Three major hurricanes hit the Caribbean island, causing an estimated $10 billion damage.

The long-term average for the Atlantic hurricane season is about 10 tropical storms and six hurricanes. But experts said a period of heightened Atlantic hurricane activity started around 1995 and was expected to last 25 to 40 years.

London-based Tropical Storm Risk Monday forecast 15 tropical storms, 7.8 hurricanes and 3.6 major hurricanes.

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