The boy may be returning for next fall and winter, and that means another season of discontent for winter weather fans. The boy is El Nino, Spanish for the "the child," and the phenomenon is the abnormal warming of the equatorial Pacific Ocean water temperature. This warming is something that naturally occurs every three to five years, and when it does it usually grabs headlines.

El Nino was given its name by Peruvian fishermen who noticed that around the time of Christmas the fishing off the coast of their country often became very poor. Warm sea-surface temperatures would move in and the fish would head for deeper and colder water. The child the fishermen referred to was the Christ child since this was a Christmas event. It didn't happen every year, but often enough to ruin the fishing.

We now know that this warming is a cyclical event, often alternating with an abnormal cooling of the Pacific waters called a La Nina (the little girl). Normally the water around the equator in the western Pacific Ocean is 6 to 10 degrees warmer than the same latitude water in the eastern Pacific. The trade winds steadily blow from east to west along the equator, pushing warm surface ocean water to the western side of the Pacific Ocean. Every few years the atmospheric pressure systems reverse themselves and the steady east trade wind relaxes. That allows the warm water to "slosh" back to the eastern Pacific, just like tipping a fish tank full of water from side to side and watching the water slosh back and forth.

Scientists aren't entirely sure why this switch in the pressure pattern takes place, but they can monitor it more easily now with instrument-equipped buoys floating along the equatorial Pacific Ocean. These buoys send their data to orbiting satellites, which relay the information around the world. Weekly sea-surface temperature charts are prepared and compared to previous charts. The progress of this "sloshing" of warm water can be watched very closely.

The buoys are beginning to show another warm-up, and computer models that simulate the ocean currents are predicting another El Nino this fall and winter. Long-range seasonal maps have already been constructed, with the results typical of an El Nino winter: wet weather stretching from Arizona through Texas and Florida, dry weather across the northern tier of United States. Warmer-than-normal temperatures from November through next March are expected in the northern Plains and Upper Midwest.

To watch the progress of the Pacific sea-surface temperatures and to learn more about El Nino and his sister La Nina, go to the Climate Prediction Center web site at www.cpc.ncep.noaa.gov.