What is El Niño?
Picture a huge band of ocean along the equator, stretching from Australia to Peru. Most of the time, the trade winds push the warm surface water there toward Asia. When those winds weaken, the warm water spreads back toward the central and eastern Pacific, off the coast of South America. That is El Niño.
The name comes from Peruvian fishermen, who noticed the warmer water around Christmas and named it after the Christ child. Today we know it is part of a natural cycle called ENSO (El Niño–Southern Oscillation), which swings between three phases: El Niño (warmer water), La Niña (cooler water) and neutral. An El Niño typically lasts nine months to a year and comes back every two to seven years on average.
How do we know it has arrived?
Scientists track the sea surface temperature in a patch of the Pacific called Niño 3.4. When it stays at least half a degree Celsius above normal for several months in a row, and the winds and air pressure shift along with it, NOAA officially declares El Niño.
Why does something so far away matter where I live?
Warmer water heats the air above it and builds rain clouds where there were none. That reshapes the big wind currents of the atmosphere, including the jet stream, a bit like a rock changing the course of a river. The effect travels thousands of miles and changes where storms go across the Americas.
El Niño vs. La Niña
| El Niño | La Niña | |
|---|---|---|
| Central Pacific | Warmer | Cooler |
| Southern U.S. winter | Wetter, cooler | Drier, warmer |
| Northern U.S. and Canada winter | Milder | Colder |
| Atlantic hurricanes | Fewer | More |
Want to see where things stand now? Check today's dashboard.