WASHINGTON -- The climate phenomenon known as La Nina seems likely to develop during the next six months and continue through next winter, government forecasters said Friday.
La Nina is the opposite of the El Nino phenomenon that has brought severe weather to wide areas over the past year.
While an El Nino is characterized by unusually warm water in the eastern Pacific Ocean, water in the same area becomes colder than normal in La Nina. Both conditions affect the atmospheric circulation overhead and can have an impact worldwide.
During a La Nina year, winter temperatures tend to be warmer than normal in the Southeastern states and cooler than normal in the Northwest.
In its latest forecast, the National Center for Environmental Prediction said the changing conditions in the Pacific "indicate that a cold episode will likely develop during the next six months and continue through the northern 1998-99 winter."
El Nino, which has been blamed for the series of severe storms that battered California, as well as sundry other weather problems, has petered out in recent months. Since El Nino years tend to have fewer than normal hurricanes in the Caribbean and Atlantic Ocean, that raises concerns that more storms may occur this summer.
The warm waters of El Nino generate moist, rising air that can change the patterns of the jet stream which steers weather.
In La Nina years, ocean temperatures are colder and the air overhead drier since there is less evaporation. This tends to result in weaker wintertime jet streams over the central and eastern Pacific and stronger monsoons over Australia, Southeast Asia, South and Central America and Africa.
La Ninas do not always follow El Nino episodes. More often ocean conditions return to a relatively normal state, but scientists do not yet fully understand the reasons for the changes.
The name La Nina, Spanish for little girl, was chosen by researchers to indicate the condition is the opposite of El Nino, which means little boy. That name had been picked by South American fishermen, who tended to notice the change in conditions around Christmastime, and named it after Baby Jesus.