La Niña's exit could mean drier winter

WASHINGTON -- La Niña, the Pacific Ocean cold-water mass blamed for last year's droughts and intense hurricanes in parts of the United States, appears to be just about out of gas, NASA scientists reported yesterday.

For the northern West Coast, the disappearance of La Niña should produce drier and warmer weather next winter, said David Adamec, a research oceanographer at the National Aeronautics and Space Administration's Goddard Space Flight Center in Greenbelt, Md.

With La Niña disappearing altogether in the eastern Pacific and fast dissipating in the rest of the ocean, San Francisco and Seattle could experience milder winter weather again next year, he said.

"We had a pretty mild winter here this year," said Christopher Hill, director of the National Weather Service office in Seattle.

The typically colder and wetter winter of La Niña may have been offset by a more localized weather phenomenon known as the Pacific Decadal Oscillation, Hill said. That cycle appears to be entering a warming phase, he said, which may have contributed to a relatively mild winter.

"We don't really know yet what's going to happen next winter," Hill said.

Because La Niña acted as a rain inhibitor in wide areas of the South and Midwest, the disappearance of this equatorial Pacific Ocean weather phenomenon could help farmers affected by severe drought conditions.

The loss of La Niña also could be a boon to Atlantic coastal regions such as North Carolina, which were swamped by flooding after Hurricane Floyd last year. Without La Niña, hurricanes are somewhat less likely to form. And if they do, Adamec said, they are less likely to strike land.

At the same time, NASA scientists who review spacecraft data and ocean buoy observations have noted a rise of four degrees in the water temperature off the Pacific coast of South America.

Does this portend a return of El Niño, which racked the West Coast with devastating storms and floods in 1997?

"The potential is there and you need to monitor it," Adamec said. "But saying it's going to happen is premature. It's premature to say it's likely."

Under normal conditions, winds blow east to west across the equatorial Pacific. But under El Niño, winds are either reduced in velocity and magnitude or they reverse direction, Adamec said. This translates into stormy weather on the Pacific Coast.

El Niño's warm-water mass "can set a process in motion which brings warm water from west to east" Adamec said.

Researchers will monitor the water temperatures and atmospheric conditions for two to three months to determine whether El Niño is, in fact, making a reappearance. "The atmosphere has a mind of its own sometimes," Adamec said.

Reporter Dan Freedman can be reached at 202-298-6920 or dan@hearstdc.com

P-I reporter Tom Paulson contributed to this report.