What is El Niño?

El Niño is part of a natural climate pattern known as the El Niño–Southern Oscillation (ENSO). It occurs approximately every two to seven years and brings warmer-than-normal ocean water to parts of the equatorial Pacific Ocean.

The strongest recent El Niño events, in 1997–1998 and 2015–2016, significantly altered weather patterns worldwide. Their impacts included fires in Indonesia and the Amazon, drought-related crop failures in southern Africa, and heavy rain and coastal flooding in Southern California. Scientists say the current El Niño event could be comparable to those large-scale events.

How El Niño develops

El Niño events result from a feedback loop between the atmosphere and the ocean. Trade winds typically push warm water toward the western Pacific, where sea levels are higher than in the eastern Pacific.

When the trade winds weaken, the warm water begins moving eastward. This movement can cause the winds to weaken further or even reverse, allowing more warm water to shift toward the central and eastern Pacific. The cycle intensifies as ocean temperatures rise and heat accumulates across the region.

However, every El Niño develops differently. Its effects depend on where the Pacific Ocean warms and how the atmosphere responds.

“The search for a ‘typical’ El Niño is very elusive. They’re all different in terms of where they land and how their effects play out.”

Josh Willis, project scientist for the surface mission at NASA’s Jet Propulsion Laboratory

How satellites track El Niño conditions

Altimeter satellites help scientists identify differences between El Niño events by measuring sea-surface height. Water expands as it warms, so higher-than-normal sea levels in the central and eastern equatorial Pacific can indicate a buildup of heat linked to El Niño.

The map above shows sea-level height anomalies across the Pacific on October 13, 1997, on the left, and October 12, 2026, on the right. The measurements came from the TOPEX/Poseidon and Sentinel-6 Michael Freilich satellites and were processed by scientists at NASA’s Jet Propulsion Laboratory.

Red areas show sea levels that were higher than average. White represents near-normal conditions, while blue indicates lower-than-average sea levels. Seasonal cycles and long-term trends were removed to emphasize sea-level anomalies associated with El Niño and other short-term natural phenomena.

How the 2026 El Niño compares with 1997–1998

The 2026 El Niño developed much more suddenly than the 1997–1998 event. However, as of October, Josh Willis said the two events could have similar effects because they share comparable sea-level patterns: lower levels in the western Pacific, higher levels in the east, and warm water extending toward the coast of South America.

During the 1997–1998 El Niño, this pattern contributed to substantial rainfall in California and the southern United States.

“What’s unique about altimetry is that we have 35 years of records from nearly identical satellites flying in roughly the same ground orbit, and each mission overlaps with the next. This allows us to look back and compare this El Niño event to what happened in 1997. And now this El Niño event is trending even bigger.”

Josh Willis, NASA’s Jet Propulsion Laboratory

How the 2026 El Niño differs from 2015–2016

The 2015–2016 El Niño was also highly disruptive, but its pattern was different. Sea-level anomaly data from October 12, 2015, collected by the Jason 2 satellite, showed unusually warm, elevated water along the equator that did not extend toward South America as strongly as it did during other El Niño events.

As a result, rainfall during the 2015–2016 winter was more concentrated in Central America and the southeastern United States, while Mexico experienced widespread flooding.

What NOAA predicts for winter 2026–2027

According to the NOAA El Niño outlook issued on October 8, 2026, there is an 83 percent chance of a strong to very strong El Niño during the first three months of 2027.

The precise effects of the event during the winter of 2026–2027 and beyond remain uncertain. El Niño’s influence spreads through a chaotic atmosphere, and weather signals can become less clear as they move beyond the tropics.

“It’s always a bit of a roll of the dice here. Just because this El Niño is similar to 1997 doesn’t mean it will be exactly the same. That’s just our best guess at this point.”

Josh Willis, NASA’s Jet Propulsion Laboratory