Federal climate experts say a weak version of the El Niño climate phenomenon may be forming in the Pacific Ocean.

If the process continues, the United States could experience mild impacts in late winter or early next spring, according to forecasters at the Climate Prediction Center.

El Niño is an abnormal warming of the ocean temperatures across the eastern tropical Pacific that can affect weather around the globe. Episodes occur about every four-five years.

The last El Niño, in 1997-8, set off fatal storms, heat waves, fires, floods and drought around the world resulting in an estimated $32 billion in damage.

In North America the result of an El Niño tends to include the movement of abnormally warm air into western Canada, Alaska and the extreme northern portion of the contiguous United States. Storms also tend to be more vigorous in the Gulf of Mexico and along the southeast coast of the United States, resulting in wetter than normal conditions in that region.

The report from the National Oceanic and Atmospheric Administration comes two weeks after the World Meteorological Organization in Geneva, Switzerland, issued a similar warning.

The U.S. researchers cautioned that at this early stage there is a great deal of uncertainty about the timing and intensity of the next El Niño.

"Although slightly warmer-than-normal ocean waters are being observed in the equatorial Pacific, current conditions in the tropical Pacific are closer to neutral than either El Niño or La Niña," said Climate Prediction Center meteorologist Vernon Kousky.

La Niña is a cool-water reversal of El Niño conditions that can also disrupt weather.

August data indicate that the waters in the central equatorial Pacific, near the International Date Line, have averaged at least 84 degrees Fahrenheit, about 1.0 degree above normal.

But the researchers said they have not seen other changes in the global temperature and precipitation pattern that would be consistent with an El Niño.

An El Niño normally includes a persistent weakening of the trade winds, increased precipitation over the warmer than normal waters, sustained sea surface temperatures of at least a degree Fahrenheit above normal for a number of consecutive months and changes in air pressure at various locations.