Fasten your seatbelts. Weather forecasters at the National Oceanic and Atmospheric Administration (NOAA) announced today that another La Niña is developing in the tropical Pacific Ocean, right behind a similar pattern that took place last year. Although not as notorious as its better-known cousin, El Niño, La Niña nevertheless could unleash weather-related damage and hardship from Indonesia to the southeastern United States.
The Pacific is hardly peaceful when it comes to spurring weather-related phenomena. When warmer-than-average waters appear in the ocean's equatorial regions, the resulting El Niño, or "little boy," pattern can cause severe storms and massive flooding in western North and South America--and burning droughts in eastern Australia. Its counterpart, La Niña, or "little girl," caused by colder-than-average Pacific waters, is no slouch, either. It tends to dry up much of North and South America and spur more frequent tornadoes in the U.S. Midwest and severe hurricanes in the Atlantic Ocean.
La Niña conditions appeared last year across the Pacific basin, coinciding with severe drought conditions in the Southeastern U.S. That nearly exhausted Atlanta's reservoirs, for example, and threw New Zealand into an economic recession. Then, for a while, it looked like the pattern was dissipating, as water temperatures in the central Pacific began to rise. Now, that trend has suddenly and surprisingly reversed. Satellite and buoy monitoring efforts have recorded temperatures as much as 1.1°C lower than normal for the region. (A La Niña is considered under way when average water temperatures drop below 0.5°C.)
As a result, NOAA forecasters now predict that La Niña-related conditions will continue at least through March. They expect heavier rainfall in Indonesia, possibly accompanied by flooding, and drier weather in the central and eastern Pacific, meaning drought conditions. Lighter snowfall and smaller snowmelt could return to the U.S. Southwest. Farther east, there should be greater rainfall in the Ohio and Tennessee River valleys, again with the potential for damaging floods in those areas, and reservoirs in the Southeast could be hitting bottom once more. NOAA also predicts a colder-than-normal winter in the Pacific Northwest and warmer temperatures across the southern half of the country.
Although a La Niña intermission like last summer's is unusual, a prolonged stretch with predominately colder waters in the tropical Pacific is not, says climate scientist David Battisti of the University of Washington, Seattle. The break may have thrown off forecasters, but now "it looks like a pretty standard La Niña situation to me," he says.