La Nina Event Could Be Developing

Observed sea surface temperatures on August 29, 2007. CREDIT: NOAA

La Niña, El Niño’s cooler cousin, could be heading our way again, sparking hurricanes and generally messing up the Western Hemisphere's weather, government scientists announced today.

La Niña refers to the periodic cooling of ocean surface temperatures in the central and east-central equatorial Pacific that typically occurs every three to five years. El Niño events, with warmer water, fuel high-level winds that cross America and tend to lop off the tops of Atlantic storms and keep them from developing into hurricanes. La Niña events tend to favor the development of hurricanes in the Atlantic.

In their monthly watch of the El Niño/Southern Oscillation (ENSO) phenomenon, scientists with the National Oceanographic and Atmospheric Administration (NOAA) said that conditions looked ripe for the development of a La Niña episode, though it is not yet a certainty.

"While we can't officially call it a La Niña yet, we expect that this pattern will continue to develop during the next three months, meeting the NOAA definition for a La Niña event later this year," said NOAA scientist Mike Halpert.

The development of La Niña conditions is supported by below-normal sea surface temperatures across the central and eastern equatorial Pacific and stronger-than-average easterly winds across the west-central equatorial Pacific.

“Nearly all operational dynamical models, including the National Centers for Environmental Prediction’s Climate Forecast System and many of the statistical models, also favor a La Niña event,” said Halpert.

With La Niña developing, seasonal forecasters expect wetter-than-normal conditions in the Pacific Northwest and drier-than-normal conditions in the already drought-stricken southwestern United States this fall.

“These conditions also reinforce NOAA’s August forecast for an above normal Atlantic hurricane season,” said Gerry Bell, Ph.D., NOAA’s lead seasonal hurricane forecaster.

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