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Hurricane Forecasts Higher as Atlantic Basin Rumbles

August 13, 2012
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Tropical storm activity in the Atlantic basin was somewhat more threatening last week, with one hurricane slamming into the coast of Mexico and other systems churning across the Atlantic. Meanwhile, two prominent forecasters said they expect more storms to form this year than they had previously forecast.

The chances of an above-normal Atlantic hurricane season have increased, according to the National Oceanic and Atmospheric Administration (NOAA), which raised its tropical forecast to a total of 12-17 named storms, including five-eight hurricanes, two-three of them major (Category 3 or higher).

NOAA's updated outlook still indicates a 50% chance of a near-normal hurricane season, but the forecasters said the chance of an above-normal season have increased to 35% and the chance of a below-normal season has decreased to 15% since NOAA's initial outlook was issued in May. In that forecast, NOAA said there was a 70% chance of nine-15 named storms in the Atlantic Basin, including four-eight hurricanes, with one-three major hurricanes (see NGI, May 28).

"We are increasing the likelihood of an above-normal season because storm-conducive wind patterns and warmer-than-normal sea surface temperatures are now in place in the Atlantic," said Gerry Bell, lead seasonal hurricane forecaster at NOAA's Climate Prediction Center. "These conditions are linked to the ongoing high activity era for Atlantic hurricanes that began in 1995. Also, strong early-season activity is generally indicative of a more active season."

Forecasters at Colorado State University (CSU) expect a total of 14 named storms in the Atlantic Basin this year, including six hurricanes, two of them major, a slight increase from activity they predicted at the beginning of the 2012 hurricane season (see NGI, June 4) and about the same numbers experienced in a typical season over the past six decades.

"We anticipate a slightly below average remainder of the hurricane season this year due to an anticipated weak El Nino event and a tropical Atlantic that is less favorable than in the past two years," the CSU forecast team said last week. "This forecast is a slight increase from activity predicted in early June due to a slower-than-anticipated onset of El Nino and a somewhat more favorable tropical Atlantic than observed earlier this year."

In April the CSU forecast was 10 named storms, including four hurricanes, two of them major (see NGI, April 16); by the official start of the Atlantic hurricane season on June 1 that forecast had been nudged higher to 13/5/2.

The Atlantic hurricane season got off to an early start this year with the formation of tropical storms Alberto and Beryl in May -- only the third time that two named storms have formed prior to June 1, the official start of the season, NOAA said. The season's third named system, Chris, formed southeast of the Canadian Maritimes June 19 and, despite becoming the season's first hurricane for a few hours on June 21, never threatened the North American mainland. Debby, the fourth named storm of the 2012 season, formed near the Yucatan Peninsula June 23, forcing offshore GOM oil and gas operators to evacuate workers from platforms and shut in production temporarily (see NGI, July 2).

Despite that quick start and its increased forecast numbers, NOAA said an El Nino event, which usually limits tropical storm activity, is likely to develop in the Pacific Ocean this month or next.

"El Nino is a competing factor, because it strengthens the vertical wind shear over the Atlantic, which suppresses storm development," Bell said. "However, we don't expect El Nino's influence until later in the season."

Tropical activity, which had been relatively quiet throughout July, picked up in the first week of August, with several storm systems churning through the Atlantic. On Friday the National Hurricane Center (NHC) was tracking Tropical Depression Seven about 775 miles east of the Windward Islands. The depression was moving west at 23 mph with maximum sustained winds of 35 mph on a track that was expected to bring it about midway between Venezuela and the Dominican Republic by Monday morning and could have it approaching the Yucatan peninsula by midweek, NHC said.

"Some strengthening is possible during the next 48 hours...and the depression could become a tropical storm before reaching the lesser Antilles," NHC said Friday morning.

On the other side of the Atlantic, NHC was keeping an eye on a low pressure system located between the Cape Verde Islands and Africa. The low, which was producing a small area of showers and thunderstorms, had a 50% chance of becoming a tropical depression over the weekend, according to NHC.

The remnants of Ernesto, which formed Aug. 2 and had reached hurricane status for a few hours beginning last Monday night, were dumping heavy rain on central Mexico on Friday. Maximum sustained winds were down to 25 mph. A surface trough associated with the remnants of the season's sixth named storm, Florence, was producing minimal shower and thunderstorm activity several hundred miles north of Puerto Rico, NHC said.

The probability of U.S. major hurricane landfall and Caribbean major hurricane activity for the remainder of the season is estimated to be slightly below its long-period average, according to CSU. There is a 28% probability of a major hurricane making landfall on the Gulf Coast from the Florida Panhandle west to Brownsville, TX; a 28% probability of a major hurricane making landfall on the East Coast; and a 48% probability of a major hurricane coming ashore anywhere on the U.S. coastline -- all below the average over the last century and unchanged from the previous CSU outlook -- the forecasters said. The probability of at least one major hurricane entering the Caribbean is 39%, also unchanged from the previous CSU prediction.

The consensus forecast this year has been that the hurricane season is likely to produce fewer tropical storms than seen during the last few years. Last month Weather Services International (WSI) said more named storms than it had previously forecast are likely to form in the Atlantic Basin this year (see NGI, July 30). The WSI forecast team expects 13 named storms, including six hurricanes, three of them major.

While last year's Atlantic hurricane season didn't bring many tropical storms to Gulf of Mexico energy interests or the North American mainland, it did produce the third-highest number of tropical storms since records began in 1851 and continued a trend of active hurricane seasons begun in 1995 (see NGI, Dec. 5, 2011). Many of the storms stayed out in the middle of the Atlantic.

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