El Niño in two minutes
El Niño is a natural warming of the sea surface in the central and eastern tropical Pacific Ocean. Every few years, the trade winds that normally push warm water west towards Asia weaken. Warm water spreads east towards South America, and the areas of heavy tropical rain move with it.
Because tropical rain drives the atmosphere's circulation, the change is felt far away:
- Often drier: Indonesia, the Philippines, eastern Australia, southern Africa, northern South America, Central America and parts of India during the monsoon.
- Often wetter: the coasts of Peru and Ecuador, the southern United States in winter, and parts of East Africa in the short rains.
- Warmer worldwide: El Niño releases heat from the ocean, so the year after a strong El Niño is often a record-warm year globally.
These are tendencies, not rules. Every El Niño is different, and other factors also shape each season. That is why each country page shows both the current forecast odds and how often past El Niños went each way there.
How it is measured
NOAA uses the Oceanic Niño Index (ONI): the 3-month average sea-surface temperature difference from normal in the central Pacific (the "Niño 3.4" area). An El Niño is declared when the ONI stays at +0.5 °C or more for five overlapping 3-month seasons. Strength is graded weak, moderate, strong or very strong (2.0 °C and above).
How long it lasts
El Niño events usually develop in the northern summer, peak around December, and fade by the following northern spring or summer. They occur every two to seven years. The current event's latest ONI is 2.46 °C (ASO 2026, very strong). See the status page for NOAA's latest assessment.