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This morning, before writing this column, I spent a considerable amount of time watering my wilting garden. Meanwhile, the New York Yankees have been rained out for their third consecutive game. And out in California? Rain, no rain, rain, no rain... Why are we suffering such severe weather this summer? In case you have not heard, we are experiencing a weather phenomenon called El Nino. What is El Nino, and How Long Will This Last? According to Michael McPhaden, director of the Tropical Atmosphere Ocean Array, an El Nino is born when west-blowing Pacific trade winds relax or reverse. Without the wind at its back, seawater that typically piles up on the jagged western edge of the Pacific -- around Indonesia, the Philippines and Australia -- slides back toward the Americas. The sliding water moves in what scientists call Kelvin waves. "It pushes the cold water down. That causes the initial warming," said McPhaden. At the same time, the Pacific reacts to the lost wind by building another series of waves under water. Called , they roll west toward Indonesia, the Philippines and Australia. Eventually, the series of waves strikes the coasts of those countries. Then, it reverses and heads back toward South America, traveling along the equator. "As it passes," McPhaden said, "it leaves cold water closer to the surface." El Nino normally occurs around Christmas and usually last for a few weeks to a few months. Sometimes an extremely warm event can develop that last for much longer time periods. A strong El Nino developed in 1991 and lasted until 1995. We are apparently experiencing one of these stronger El Ninos, as this one has lasted for nearly six months . But how long will this last? And then what? The Onset of La Nina After an El Nino event, weather conditions usually return to normal. However, in some years the trade winds can become extremely strong and an abnormal accumulation of cold water can occur in the central and eastern Pacific. This event is called La Nina. Where El Nino refers to a body of unusually warm water astride the equator by South America, La Nina describes a sea that's abnormally cool. Two independent computer models that forecast El Nino see on the horizon a pronounced cooling of the same area of the Pacific. Sometimes, the cold water is just enough to return ocean temperatures to normal. Not always. "Sometimes, it overshoots," McPhaden said. "That would bring a La Nina after El Nino." "The models say . . . there will be a cold effect sometime next year -- magnitude and timing to be determined," said Tim Barnett, one of the model makers at Scripps Institution of Oceanography in La Jolla. The other model with the La Nina forecast comes from the Center for Ocean-Land-Atmosphere Studies, a research institute in Calverton, Md. Climate experts agree that the forecasts should be viewed with considerable caution. Even without consulting computers, it's a reasonably safe assumption that the present warm spell will be followed, eventually, by a cold one. That's because the makings of a La Nina are built in to an El Nino. As McPhaden puts it, "The seeds for the demise of El Nino are sown even at its onset." So maybe it's time we stopped blaming El Nino for all of our maladies. From now on, we can start blaming the onset of La Nina. Most people will not notice the transition from El Nino to La Nina, as the weather will still be hot and there will initially be increased rainfall, particularly in California, which we may from this point forward refer to as CaliforNina. Level: Junior (college) Subject: Science Writing COUNTRY: USA Is La Nina Upon Us?