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El Niño tempered hurricane season 2006

Despite catching a break, experts caution we’re still in a period of heightened storm activity

Despite catching a break, experts caution we’re still in a period of heightened storm activity

Thank El Niño for the mild 2006 Atlantic hurricane season. It was less active than expected, with nine named storms. Five were hurricanes, and two were major ones — Category 3 or stronger. None of the hurricanes and just three tropical storms hit the United States.

That’s a far cry from the record 2005 season, when 28 named storms formed. Fifteen of those were hurricanes, and seven were major ones, including Katrina, the behemoth that caused $96 billion in damage to the Louisiana and MississippiGulf coasts. A rapidly developing El Niño last summer spared us the onslaught that had been predicted in 2006, says Gerry Bell, lead forecaster on the National Oceanic and Atmospheric Administration’s Atlantic hurricane seasonal outlook team. NOAA had expected 13 to 16 named storms, eight to 10 of them hurricanes and four to six major ones.

Bell says a series of warm-water waves — not an unusual phenomenon — rippled eastward across the central and eastern Pacific, raising the water temperature a degree or two and creating conditions favorable for El Niño. The warm water spawned more thunderstorms over the Pacific, which caused weather changes in the Caribbean — sinking air and stronger west-to-east winds in the upper atmosphere. Sinking air and upper-level winds are death to hurricanes, Bell says. They interfere with air circulation that fuels thunderstorms.

“If you can’t get thunderstorms, you don’t get hurricanes,” he says.

Sinking air in the middle and upper atmosphere keeps warm air from rising, which is vital to thunderstorm formation. “It’s kind of like holding a beach ball down in the bottom of a pool,” he says. “It can’t shoot up.” Upper-level winds also disrupt the structure of thunderstorms, “shearing” the column of warm air rising at the center.

Another factor in 2006: The Bermuda High was a little farther east than usual, creating favorable conditions for a strong low along the East Coast. The low generated westerly winds that steered hurricanes into the Atlantic and away from the United States, according to NOAA.

Bell says El Niño episodes, which develop every three to five years, also dampened the level of Atlantic hurricane activity in 1997 and 2002. The 2006 storm tally is a little less than what has been the average since 1950: 11 named storms, six of them hurricanes, two to three of them majors.

A summer El Niño typically begins to fade the following April or May and usually is all but gone with the onset of the June-to-November hurricane season. It was too early to say if there would be any remaining El Niño effects in 2007, according to Bell, but he says not to count on its moderating effect. “This is kind of a one-off thing,” he says.

He recommends making good use of winter and spring to prepare for this year’s hurricanes. He says the East Coast and Caribbean still are in a 25- to 40-year cycle of heightened hurricane activity, and the cycle started in 1995. University of Colorado forecaster William Gray predicted late last year that 2007 would bring above-average hurricane activity, with 14 named storms, including three major hurricanes and four others.

“We got a break [in 2006],” Bell says. “We were very fortunate.”