September 6, 2007 — Scientists with NOAA’s Climate Prediction Center, in today’s release of its monthly El Niño/Southern Oscillation (ENSO) Diagnostic Discussion, say that La Niña is on its way. (Click NOAA image for larger view of observed sea surface temperatures on August 29, 2007. Please credit “NOAA.”)
“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 Mike Halpert, acting deputy director of the Climate Prediction Center in Camp Springs, Md.
La Niña refers to the periodic cooling of ocean surface temperatures in the central and east-central equatorial Pacific that occur every three to five years. NOAA declares the onset of a La Niña event when the three-month average sea-surface temperature departure exceeds -0.5 degrees Celsius (-0.9 degrees Fahrenheit) in the east-central equatorial Pacific [between 5 degrees North and 5 degrees South and 170 degrees West - 120 degrees West].
The development of La Niña conditions is supported by increasing 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 U. S. 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.
The Climate Prediction Center routinely publishes an assessment of ENSO conditions each Monday and the next official ENSO Diagnostic Discussion will be issued on October 11, 2007. The El Niño/Southern Oscillation Diagnostic Discussion is a product of the Climate Prediction Center in association with its funded institutions.
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