New El Nino Verified; Could Be Disruptive

For the third time in 10 years, a huge expanse of unusually warm water has developed in the equatorial Pacific, setting in motion a so-called El Nino system that could disrupt normal weather patterns around the world, National Weather Service scientists said Monday.

Evidence of another of the periodic upsets had been accumulating for several months. After analyzing satellite data and other information collected in December, the weather service’s Climate Analysis Center concluded Monday that the system has formed and probably will reach its peak in the next six months.

Typically, the phenomenon produces abnormally warm winters in southeastern Alaska, the western and eastern regions of Canada and the northern tier of the contiguous United States. At the same time, areas from Arizona to Florida and along the south Atlantic coast experience cooler temperatures and greater rainfall.

The effect on California is uncertain. Past El Ninos have produced both very wet and very dry weather.

A severe El Nino in the winter of 1982-83 brought memorable storms to the state, but another in 1986-87 went nearly unnoticed.

Beginning late in 1991, a series of storms has brought substantial rainfall to California, but weather service scientists declined Monday to attribute them, or the recent record-breaking floods in Texas, to the new system or to predict what the remainder of the winter will bring.

Stephanie Hunter, a meteorologist with WeatherData Inc., a private firm that provides forecasts for The Times, predicted Monday that “from Los Angeles south, it’ll be wetter than normal this year through February, with near normal temperatures . . . “

“We think this pattern is attributable to the El Nino,” she said. “There will be more rain than average but I can’t say how much more.”

The effects of an El Nino usually fade away with the coming of spring but David Rodenhuis, director of the Climate Analysis Center, warned Monday: “We should say this is still January, so hold onto your hat.”

The warming of an expanse of the tropical Pacific sometimes reaching a fourth of the way around the Earth leads to massive changes in cloud patterns and shifts in the jet stream, the high-speed, high-altitude current of air that creates weather patterns.

What happens in California’s weather in the weeks ahead largely will be determined by whether the jet stream takes an extremely northern route, creating storms in the Gulf of Alaska and warming western Canada, or remains split, as it has on occasions in past El Ninos, delivering more storms to Southern California.

The warm Pacific pool now being watched is about twice the size of the one in 1986 and 1987, and the water temperature, as high as 86 degrees, averages about 1 degree more than in January, 1987. During the severe 1982-83 El Nino, even higher water temperatures were recorded.

For now, weather service scientists said, the new El Nino could be described as “moderate” in intensity.

“We could continue on with a weather pattern like what we have been experiencing for the last six weeks,” said Edward O’Lenic, head of forecasting operations at the analysis center.

If the jet stream remains split off the West Coast, as it is now, he said, a mild weather pattern will continue to dominate most of the continent’s interior.

If it forms a single stream, then moves north into British Columbia and dives to the midsection of the United States, it would bring colder temperatures to the Great Lakes and the eastern United States.

“I suspect that we will see a flip-flop between those two patterns with a little bit of both,” he said.

On a worldwide scale, El Ninos have been associated with extreme droughts in southern Africa, Australia and the tropics of Brazil.

Formally known to meteorologists and climatologists as the El Nino Southern Oscillation, the condition also has spawned devastating floods, as it did nine years ago in Peru and Ecuador.

The El Nino in that year was estimated to have cost 1,500 lives and caused about $8 billion in damages worldwide.

Since El Ninos develop every three to five years, the system has become both a benchmark in the study of climate history and a basis for comparative analyses in forecasting. Aside from the annual seasons themselves, Rodenhuis said, the oscillation is the most important regular event in world climate.

“By studying similar past events,” he added, “our scientists have discovered El Nino precipitation and temperature patterns, which are highly consistent from one episode to another.

“Since El Nino patterns tend to persist for several months, relatively accurate long-range forecasts can be made for certain regions of the earth.”

U.S. scientists began picking up hints of warming about a year ago, and they now believe that the return to El Nino conditions were well under way by last summer.

Times staff writer Eric Malnic in Los Angeles contributed to this story.