Weak El Nino likely to form by year's end

WASHINGTON -- A weak to moderate El Nino is likely to develop by year's end, government climate experts said last week.

The climate phenomenon can affect weather around the world, but the impact should be less than during the strong El Nino of 1997-98, according to forecasters at the National Oceanic and Atmospheric Administration.

El Nino is characterized by an abnormally warm sea surface in the central equatorial Pacific Ocean. This results in increased evaporation and rising air currents that can affect the winds overhead that steer the movement of weather.

Researchers have been reporting slowly rising Pacific temperatures for the last several months. Ocean surface temperatures were more than 0.8 degree Fahrenheit above average during April over a large part of the central equatorial Pacific and as much as 3.6 degrees above average in the extreme eastern equatorial Pacific, near the coast of South America.

Also, subsurface ocean temperatures remained more than 3.6 degrees above normal in the central equatorial Pacific.

"Some events develop quickly and others, like this one, have a more gradual evolution," said Jack Kelly, director of the National Weather Service. "We are maintaining a constant watch over the conditions of the atmosphere and ocean and will continue providing guidance on potential impacts."

Harder to anticipate

Vernon Kousky of the Weather Service's Climate Prediction Center said experts have expected only a weak to moderate El Nino, given that its last appearance was so strong.

Historically, "We have not seen two strong El Ninos back-to-back," he said.

On the other hand, he said, the weaker events are "less well behaved," meaning that their impacts can occur in spurts and may be harder to anticipate in any particular area.

The last El Nino, in 1997-98, set off fatal storms, heat waves, fires, floods and drought, and caused an estimated $32 billion in property damage worldwide.