updated 2/2/2006 2:42:46 PM ET 2006-02-02T19:42:46

U.S. weather officials confirmed the arrival of the La Nina weather pattern, a mild cooling of the tropical Pacific Ocean which can affect weather in parts of the United States, Asia and South America.

The National Oceanic and Atmospheric Administration Climate Prediction Center made the announcement Thursday at the American Meteorological Society's meeting in Atlanta after confirming the slight cooling of parts of the Pacific Ocean and changes in the jet stream.

Forecasters at the meeting said the latest La Nina may last through the summer.

La Ninas tend to encourage wet weather in the Pacific Northwest and dry conditions in the South, but NOAA forecasters declined to blame current weather on the phenomena.

Internationally, La Nina typically creates more rainfall across Indonesia and northern Australia and the Amazon basin, said Edward Alan O'Lenic, chief of the operations branch of the Climate Prediction Center.

Typically in La Nina years, hurricanes are stronger and more numerous, but O'Lenic said it's too early to say what overall effects La Nina will have on the Atlantic hurricane season this year.

La Nina is the opposite of the better known El Nino, a Pacific warming. Both occur every few years and can affect weather around the world. The last La Nina occurred in 2000-2001.

Because the latest La Nina is only just starting to develop and is expected to be weak, forecasters at the NOAA Climate Prediction Center said it is too early to say how it will affect spring and summer weather.

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