Hints of El Nino surface in Pacific Ocean.

Hints of El Nino surface in Pacific Ocean

Changing climate conditions in the central Pacific, where an El Nino warming appears to be brewing, could cause abnormal weather in many regions of the world during the next year and may bring some eventual relief to drought-plagued southern Florida, more than 6,000 miles away from that portion of the Pacific.

"We're seeing signs that [an El Nino] could be getting started. Whether or not these features will persist for a sufficient amount of time so that it will develop into an El Nino -- that is still a point in question," says Vernon Kousky of the National Weather Service's Climate Analysis Center (CAC) in Washington, D.C., which released an El Nino/Southern Oscillation advisory on Feb. 16.

El Ninos, which are related to an atmospheric pressure phenomenon known as the Southern Oscillation, bring abnormally warm water to the central and eastern equatorial Pacific -- a condition that wreaks widespread changes in the world's weather. During the century's strongest El Nino in 1982-83, India and Australia suffered droughts while heavy rains pounded the west coast of South America. Mike Halpert of the CAC says that in the United States, El Nino events typically increase rainfall over Florida and the Gulf Coast, so southern Florida's dwindling freshwater reserves could benefit if an El Nino materialized over the next year.

El Nino oceanic warmings typically last 12 to 15 months and recur on average about four to seven years apart. After the last El Nino, which ran from mid-1986 through late 1987, the central Pacific turned abnormally cold as part of a climate pattern recently dubbed La Nina, whose weather effects generally contrast with those of an El Nino. When the La Nina started dying out in late 1988, ocean temperatures in the central Pacific began to rise toward normal.

The CAC advisory notes that several developments in recent months could herald the start of another warm phase. Sea-surface temperatures have risen significantly, and the equatorial trade winds, which travel east to west, have weakened. Under normal conditions the trade winds push warm surface water toward the western Pacific and keep the central and eastern portions cooler than the west. But a significant reservoir of warm water is now building in the central Pacific and may spread eastward if the trades remain weak, Kousky says.

Most climate researchers agree it is too early to tell whether a full-blown El Nino will develop. "The next two or three months are going to be a crucial time," says Maurice Blackmon of the National Oceanic and Atmospheric Administration's Environmental Research Laboratory in Boulder, Colo.

An El Nino this year would contradict several computer models that had shown promise in forecasting previous warmings. For instance, three models in the United States predicted the last El Nino three to nine months before the warming began, yet the same models currently predict that near-normal conditions will persist in the tropical Pacific for at least the next few months. One of these, a "dynamical" model at Columbia University's Lamont-Doherty Geological Observatory in Palisades, N.Y., is "predicting more or less normal conditions for the next year," says Mark Cane of Lamont-Doherty. However, a statistical model at the Max Planck Institute for Meteorology in Hamburg, West Germany, does forecast a warming for this year, Blackmon says.

If an El Nino does develop soon, it could signal some flaws in the design of the three U.S. models. Alternatively, Blackmon says, the unsuccessful predictions may stem from a lack of sufficient input on wind speeds in the remote ocean, which are measured by ships, island stations, buoys and other sources scattered sparsely over the region.