Winds blowing along the Equator above the Pacific Ocean - from South America in the east towards Asia in the west - were stronger than normal. These "trade winds" piled warm water off the coast of Asia, raising the sea surface level. In the east, near the Americas, cold water flowed upwards to the surface. During El Niño the opposite happens - weaker trade winds mean the warm water spreads out back towards the Americas, and less cold water rises towards the surface.