The National Weather Service and scientists with the National Center for Atmospheric Research had the answer some months ago, as Reader's Digest reported in its November issue.

Copyright 1998 Reader's Digest
November, 1998

"Here Comes More WEIRD Weather: Brace yourself for El Niño's bratty little sister"
By Per Ola and Emily d'Aulaire

Scanning the data unfolding on his computer screen, Michael McPhaden stopped and stared in astonishment. According to these numbers last May, surface temperatures in the tropical Pacific were dropping fast.

McPhaden, a 47-year-old climatologist at the Pacific Marine Environmental Laboratory in Seattle, knew he was seeing evidence of a dramatic event: the demise of the climatic bully El Niño and the arrival of his unruly sister, La Niña.

Using data culled from the Tropical Atmosphere Ocean (TAO) array, a system of about 70 instrument buoys anchored to the floor of the Pacific, McPhaden and climatologists around the world were tracking developments in the Pacific. Stephen Zebiak, a scientist at Columbia University's Lamont-Doherty Earth Observatory in New York, was as incredulous as McPhaden.

"My computer showed buoy readings dropping more than five degrees in just a few weeks," he recalls. By mid-June surface temperatures in an area near the equator had dropped an astounding 14 degrees Fahrenheit. By early August the area of cold surface water was still growing.

"La Niña was definitely on the move," says McPhaden.

But what, exactly, had been set in motion? And, as La Niña proceeds to steal the spotlight from her stormy sibling, what could the world expect in terms of further aberrant weather?

The El Niño ("little boy" in Spanish) that pounded the globe between the summers of 1997 and 1998 was by some measures the most powerful —and devastating—of this century. Preliminary damage estimates exceed $33 billion worldwide, not to mention the human toll exacted by resulting droughts, floods and wildfires.

Both El Niño and La Niña ("little girl") are part of a seesawing of winds and currents in the equatorial Pacific called ENSO (El Niño Southern Oscillation) that appears every two to eight years. Normally, westward-blowing trade winds caused by the rotation of the earth and conditions in the Tropics push surface water across the Pacific toward Asia. The warm water piles up along the coasts of Indonesia, Australia and the Philippines, raising sea levels more than a foot above those on the South American side of the Pacific.

As El Niño builds, the normal east-to-west trade winds wane. Like water sloshing in a giant bathtub, the elevated pool of warm water washes from Asian shores back toward South America.

During last season's cycle, surface temperatures off the west coast of South America soared from a normal high of 74 degrees to 86 degrees. This vast area of tepid water, twice the size of the continental United States, interacted with the atmosphere, creating storms and displacing high-altitude winds.

El Niño brought rain that flooded the normally dry coastal areas of Ecuador, Chile and Peru. Meanwhile, devastating droughts struck Australia and Indonesia.

Fires have destroyed some five million acres of Indonesian forest. The drought, along with an economic crisis, left about five million Indonesians in desperate need of food and water. These conditions helped set the stage for riots that led to the downfall of President Suharto.

Closer to home, more than 30 inches of rain fell on Los Angeles from July 1, 1997, through June 30, 1998, twice the normal amount. San Francisco logged 47-plus inches of rain, almost 27 more than usual. Heavy precipitation devastated crops in many parts of California.

El Niño also took the rap for severe drought and heat in Texas that raised temperatures in College Station to over 100 degrees for a record 30 days in a row last summer. The heat wave claimed some 125 lives statewide. While Florida experienced a wetter than normal winter, its lush vegetation turned to tinder during the unusually hot and dry summer, fueling wildfires that raged throughout the state.

The weather phenomenon did have its good side. El Niño strengthened high-altitude eastward winds across the tropical Atlantic that sheared off the tops of brewing hurricanes. The result was a 1997 hurricane season that was one of the quietest on record. And the northeastern United States experienced the mildest temperatures on record from January through March 1998.

Where El Niño turns typical weather patterns upside down, drying out lush rain forests and turning arid areas into wetlands, La Niña generally exaggerates conditions considered normal. Even without an active La Niña, for example, the southwest United States would return to drier conditions with El Niño's departure. Add La Niña, and dry may well turn to drought.

El Niños are not always followed by La Niñas. Nor does the strength of one necessarily reflect that of the other. Notes Michael McPhaden, "The El Niño of 1982 to 1983, previously the strongest on record, was followed by a weak La Niña." By contrast, he says, the 1986-87 El Niño was very moderate, followed by a strong La Niña that brought a terrible drought to the Midwest, costing farmers billions in lost crops.

This time around, however, scientists are watching out for two strong events in a row. "The recently defunct El Niño may have been the most powerful of the 20th century," McPhaden states. "It is being followed by what looks to be a major La Niña. By July 1998 some buoy locations in the central Pacific already showed temperatures six degrees below normal, giving us a running start on what looks to be a significant cold event. It's a climatic double whammy because we're swinging from one set of extremes to another."

Last july the first ever La Niña Summit took place at the Boulder, Colo., headquarters of the National Center for Atmospheric Research (NCAR). Scientists from 14 countries met to analyze La Niña data, aided by technology that helps them scrutinize weather patterns as never before. But nothing has proved more critical than the TAO buoy system, completed in December 1994. Previously, scientists relied on passing vessels to report water temperatures.

"It used to be hit-or-miss,"says James O’Brien, director of the Center for Ocean-Atmospheric Prediction Studies at Florida State University. "Now buoys can record changing conditions hour by hour. We know what's going on virtually as it happens." (You can follow La Niña data via the Internet at www.pmel.noaa.gov/toga-tao.)

Despite the accuracy of these instrument buoys, scientists at the summit were hesitant to make firm predictions about the coming La Niña. "Like El Niños, not all La Niñas are the same," says Kevin Trenberth, head of the climate analysis section at NCAR.

So what can we expect La Niña to bring? High pressure from La Niña will boost chances for drought in the Southwest, including Southern California, and for a drier winter across the Sunbelt to Florida. "With the dryness," says Trenberth, "comes an increased risk of wildfires throughout that region." Already drought- and heat-ridden, Texas could experience more of the same.

"With La Niña, the jet stream is pushed northward so it enters the state of Washington instead of California, swings into Canada and dips down into the Midwest," says Trenberth. "The Pacific Northwest and British Columbia are where most of the storms are likely to come pounding in this year."

Florida State's James O'Brien is forecasting cold weather from Washington State to the Great Lakes. "It may be time to bring out the snow blowers,"he says. "It's going to be a great ski season in the Pacific Northwest."

Though La Niña's effects are weaker in the Northeast, scientists are predicting the return of a normally cold and snowy winter in New York and New England.

The more accurately scientists can forecast La Niña, the more people can prepare for it, a major goal of the International Research Institute for Climate Prediction and its director, Antonio Moura. "We want to understand the impacts of both La Niña and El Niño," says Moura. "When you know it's going to rain more, you might plant rice instead of cotton, or institute mosquito-control measures. You might even do something as simple as making sure your gutters are clean for the coming rains."

In anticipation of this winter’s La Niña, the Seattle-Tacoma International Airport bought an extra supply of de-icing material. Notes McPhaden, "It's a perfect example of a low-cost procedure that could ultimately save millions of dollars by keeping air traffic moving."

There are countless people and businesses that could benefit from advances in climate prediction, says Stephen Zebiak. "Tourist boards, commodities traders, power-company officials, and homeowners, can all profit from knowing that La Niña is likely to strike."

In the meantime, one thing is clear: El Niño's mischievous sibling is at our doorstep, and ready to stir up some more weird weather.