NASA Science Uses 35 Years of Sea Data to Compare Today’s El Niño

How El Niño builds

El Niño is a natural climate pattern that occurs about every two to seven years, warming parts of the equatorial Pacific. Its development involves a feedback loop: weakening trade winds allow warm water to move east, which can weaken the winds further and intensify the buildup.

Each event differs according to where Pacific warmth gathers and how the atmosphere responds. “The search for the ‘typical’ El Niño is very elusive,” said Josh Willis, project scientist for sea level missions at NASA’s Jet Propulsion Laboratory. He said the events vary in both location and effects.

Satellites track ocean height

Altimetry satellites measure sea-surface height. As water warms, it expands, so unusually high seas in the central and eastern equatorial Pacific can indicate the heat buildup associated with El Niño.

NASA’s comparisons use observations from TOPEX/Poseidon in 1997, Jason-2 in 2015 and Sentinel-6 Michael Freilich in 2026. The maps remove seasonal cycles and long-term trends to show short-term sea-level anomalies.

Comparing three powerful events

In October 2026, the sea-level tilt and warm water extending toward South America looked similar to conditions in October 1997. The 2026 event developed much more suddenly, but Willis said it was on track to become even bigger than the 1997 event.

The 2015-16 El Niño had a different pattern: exceptionally warm, high water along the equator did not extend toward South America as much. That winter, rainfall effects were concentrated more over Central America and the southeastern United States, with significant flooding in Mexico.

Winter impacts remain uncertain

The 1997-98 El Niño brought effects including fires in Indonesia and the Amazon, drought-related crop failures in southern Africa, and heavy rain and coastal flooding in Southern California. It also brought rain to California and across the southern United States. NOAA’s October 8, 2026 outlook gave an 83 percent chance of a strong-to-very strong El Niño through the first three months of 2027. Willis cautioned that similar ocean patterns do not ensure identical weather, saying the outcome remains “a bit of a dice roll.”