Publication Date: Wednesday Oct 15, 1997

What El Nino is

The finger is an area where the Pacific Ocean currents are warmer than normal. These warm currents, which stretch westward off the coast of South America, evaporate quickly, forming warm, moist clouds that are swept northward to join the air stream that flows over the California coast in the winter.

What El Nino is not: the present warm ocean temperatures along the California coast. Nor is El Nino the atmospheric conditions over the state. Nor is El Nino an actual ocean current that moves northward along the California coast.

Forecasters say that if El Nino persists through the winter, California will get more precipitation than normal.

"It is likely we're going to have some weather problems," said forecaster Dan Kierns, with the National Weather Service in Monterey. But to attribute a storm to El Nino, he said, the storm would have to have been caused by the huge, warm, moist clouds coming up from the South Pacific and meeting the stream of air heading toward California.

Meteorologists don't know how long El Nino will last, so they can't predict the magnitude of the effect on California. If the present El Nino persists through the winter, it is reasonable to expect greater than normal precipitation, according to the weather service Web site put together by meteorologists John Monteverdi, chair of the San Francisco State Geosciences Department, and Jan Null, lead forecaster for the National Weather Service.

It is also reasonable to expect much heavier rainfall (defined as 170 percent of normal). Three of the past eight El Ninos (1957-58, 1971-72 and 1982-83) brought at least 170 percent of normal rainfall. Officials note that this is a small sample and that nothing in the past record indicates the likelihood of heavy rainfall this year, but they say the Bay Area should be prepared for a wet winter.

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