El Nino is a phenomenon where a mass of warm water moves east across the equatorial Pacific Ocean every 3 to 8 years, usually lasting about a year. It occurs when higher pressure over Asia and lower pressure over South America cause the typical easterly trade winds to weaken or reverse direction, allowing warm water to slosh back along the equatorial Pacific. This affects weather patterns and can cause flooding in some areas and drought in others.

1. El Nino mass of warm surface water moving west to east across equatorial Pacific Ocean part of larger phenomenon called El Nino – Southern Oscillation (ENSO)

10. sea surface temperature in Pacific Ocean