La Niña, which contributed to extreme weather around the globe during the first half of 2011, has re-emerged in the tropical Pacific Ocean and is forecast to gradually strengthen and continue into winter. Today, forecasters with NOAA’s Climate Prediction Center upgraded last month’s La Niña Watch to a La Niña Advisory.

NOAA will issue its official winter outlook in mid-October, but La Niña winters often see drier than normal conditions across the southern tier of the United States and wetter than normal conditions in the Pacific Northwest and Ohio Valley.

“This means drought is likely to continue in the drought-stricken states of Texas, Oklahoma and New Mexico,” said Mike Halpert, deputy director of the Climate Prediction Center. “La Niña also often brings colder winters to the Pacific Northwest and the northern Plains, and warmer temperatures to the southern states.”

Climate forecasts from NOAA’s National Weather Service give American communities advance notice of what to expect in the coming months so they can prepare for potential impacts. This service is helping the country to become a Weather Ready Nation at a time when extreme weather is on the rise.

Seasonal hurricane forecasters factored the potential return of La Niña into NOAA’s updated 2011 Atlantic hurricane season outlook, issued in August, which called for an active hurricane season. With the development of tropical storm Nate this week, the number of tropical cyclones entered the predicted range of 14-19 named storms

The strong 2010-11 La Niña contributed to record winter snowfall, spring flooding and drought across the United States, as well as other extreme weather events throughout the world, such as heavy rain in Australia and an extremely dry equatorial eastern Africa.

La Niña is a naturally occurring climate phenomenon located over the tropical Pacific Ocean and results from interactions between the ocean surface and the atmosphere. During La Niña, cooler-than-average Pacific Ocean temperatures influence global weather patterns. La Niña typically occurs every three-to-five years, and back-to-back episodes occur about 50 percent of the time. Current conditions reflect a re-development of the June 2010-May 2011 La Niña episode.

NOAA's National Weather Service is the primary source of weather data, forecasts and warnings for the United States and its territories. NOAA’s National Weather Service operates the most advanced weather and flood warning and forecast system in the world, helping to protect lives and property and enhance the national economy. Visit us online at weather.gov and on Facebook.