La Nina shouldn't affect Atlantic hurricanes -NASA

WASHINGTON, May 5 (Reuters) La Nina, a Pacific Ocean phenomenon that can help form Atlantic hurricanes, is not expected to be a factor this season, good news after last year's disastrous storm season.

La Nina, Spanish for ''the girl,'' refers to a pattern of usually cold surface temperatures in the eastern tropical Pacific. In North America, it has been known to contribute to droughts in the West and to spur hurricanes in the East.

That happens because La Nina tends to push high-altitude jet stream winds to the north, away from the customary hurricane-forming areas, David Adamec, an oceanographer at NASA's Goddard Space Flight Center outside Washington, said yesterday.

Jet stream winds can rip the tops off developing hurricanes, and without those winds, hurricanes can form unimpeded, Adamec said by telephone.

''La Nina gives a little extra kick, keeping the jet streams away,'' he said.

There have not been strong La Nina patterns in the past two years, Adamec said, but ''it has not helped the situation.'' The 2005 hurricane season was the costliest and most destructive on record, with 27 named storms, of which 15 became hurricanes. Hurricane Katrina alone caused billion in damage, killed about 1,300 people and devastated New Orleans and parts of the US Gulf Coast.

A patch of colder-than-usual surface water in the eastern Pacific looked very much like a La Nina pattern earlier this year, Adamec said, but that had now warmed up to normal, leading scientists to believe it will not have an impact on this year's Atlantic storms.

''The fact that the cold water has disappeared now ... gives you a lot more confidence it's not going to come back,'' he said.

LA NINA AND EL NINO La Nina is different from the El Nino weather pattern, which starts as a patch of warmer-than-usual water in the eastern tropical Pacific, said Bill Patzert of NASA's Jet Propulsion Laboratory in Pasadena, California.

El Nino, which means ''the boy,'' can bring unusually warm weather and storms to the American West, but it pulls jet stream winds into hurricane-forming areas, Patzert said in a telephone interview.

''We cringe in California when somebody says El Nino,'' Patzert said. ''El Nino is the blessing for hurricane country and La Nina is the curse.'' No Atlantic hurricanes came ashore in 1997 and 1998, when there were strong El Nino patterns, Adamec said.

A noted US forecasting team projected this year's storms would not be as severe as last year's, with 17 named storms expected to form in the Atlantic basin during the six-month season, which officially begins on June 1.

More information and images are available online at http://www.nasa.gov/vision/earth/lookingatearth/laninateffect.html.

Reuters VJ VP0423