During El Nino and La Nina years...

The Southern Oscillation is the official term used to describe specific quirks in pressure patterns across the tropical Pacific. Pressure areas between Darwin, Australia and the east central Pacific, near Tahiti, are studied. When pressure is low in one area, it is high in the other, and vice versa. Sea surface temperatures also fluctuate in the same way. These changing patterns effect the weather globally, particularly precipitation. Because the see-sawing effect of these pressure areas and surface temperatures fluctuate slowly, over a year’s time usually, forecasters can use Southern Oscillation data to predict global weather changes relatively far into the future.