What is El Niño?

Normally, trade winds push warm surface water westward across the Pacific toward Asia and Australia. During El Niño, these winds weaken and warm water spreads back east toward South America. This changes rainfall and storm patterns worldwide, often bringing drought to Australia and Indonesia, heavy rain to Peru and a milder winter to parts of North America. El Niño events occur irregularly every two to seven years and usually last nine to 12 months. Its cool counterpart, La Niña, brings the opposite effects, and together they form the El Niño Southern Oscillation.