The NOAA Climate Prediction Center announced today the official return of La Niña. Agency forecasters predicted La Niña was forming nearly three weeks ago. Oceanic sea surface temperatures have met the operational definition of La Niña for the November through January period. La Niña is the periodic cooling of ocean waters in the east-central equatorial Pacific, which can impact the typical alignment of weather patterns around the globe. NOAA predicts this La Niña event will likely remain into late spring, and possibly into summer. 

"In mid-January the atmosphere over the eastern North Pacific and western U.S. began to exhibit typical La Niña characteristics in response to the cooling in the tropical central Pacific Ocean," said Vice Admiral Conrad C. Lautenbacher, undersecretary of commerce for oceans and atmosphere and NOAA administrator. "This pattern will favor continued drought in parts of the South and Southwest from Arizona to Arkansas and Louisiana, and above normal precipitation in the Northwest and the Tennessee Valley area." Periodic precipitation in the drought areas and dryness in the stormy areas also are typical within the larger scale climate pattern described above.

Internationally, La Niña impacts during the Northern Hemisphere winter typically include enhanced rainfall across Indonesia and northern Australia, as well as in the Amazon Basin and in southeastern Africa and below-average rainfall across the eastern half of the equatorial Pacific and eastern equatorial Africa.

Typically, La Niña events favor increased Atlantic hurricane activity, however, Jim Laver, director of the NOAA Climate Prediction Center says, "It is too early to say with confidence what effects this La Niña event will have on the 2006 hurricane season."

La Niña events are operationally defined using the Oceanic Niño Index (ONI), which is the three-month running-mean values of sea surface temperature departures from average in the Niño 3.4 region of the central Pacific (bounded by 5N-5S, 120-170W). NOAA defines La Niña as the condition whereby the ONI is less than or equal to -0.5 degrees C. This definition was adopted by the U.S. and 25 other countries in North and Central America and the Caribbean in April 2005.

La Niña events recur approximately every three to five years. The last La Niña occurred in 2000-2001 and was a relatively weak event compared to the 1998-2000 event.

NOAA will continue to monitor this event and forecast its likely impacts. The next El Niño Diagnostic Discussion will be released on February 9, 2006. Also, NOAA will release its Spring Outlook in mid March and its Atlantic and Pacific hurricane season outlooks in mid May.

NOAA, an agency of the U.S. Department of Commerce, is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation's coastal and marine resources.

Through the emerging Global Earth Observation System of Systems (GEOSS), NOAA is working with its federal partners and nearly 60 countries to develop a global monitoring network that is as integrated as the planet it observes.