El Niño Then and Now

October 13, 1997 – October 12, 2026

El Niño is part of a natural climate pattern that occurs roughly every two to seven years, bringing warmer-than-normal water to parts of the equatorial Pacific. The most recent very strong El Niño events, in 1997-98 and 2015-16, upended weather patterns. Impacts spanned the planet, from fires in Indonesia and the Amazon, to crop failures due to drought in southern Africa, to heavy rain and coastal flooding in Southern California. The current El Niño rivals these past heavyweights.

Every El Niño grows from a feedback loop between the atmosphere and the ocean. Trade winds normally keep warm water piled up in the western Pacific, where it stands higher than in the east. When those winds weaken, that warm water begins to pulse eastward, which further weakens and sometimes reverses the winds, allowing even more warm water to move east. The cycle intensifies as waters continue to warm and pile up in the central and eastern Pacific.

But each El Niño has its own character, shaped by where in the Pacific the warmth builds 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 (JPL). “They’re all different in terms of where they land and how their impacts play out.”

Altimetry satellites can track those differences by measuring the height of the sea surface. Because water expands as it warms, higher-than-normal sea levels in the central and eastern equatorial Pacific signal the buildup of heat associated with El Niño. The maps above depict sea surface height anomalies across the Pacific Ocean on October 13, 1997 (left), and on October 12, 2026 (right). Data are from the TOPEX/Poseidon satellite and the Sentinel-6 Michael Freilich satellite, respectively, and were processed by scientists at JPL.

Shades of red indicate where sea levels were higher than average. Normal sea level conditions appear white, and lower areas are blue. Signals related to seasonal cycles and long-term trends have been removed to highlight sea level anomalies associated with El Niño and other short-term natural phenomena.

“What’s unique about altimetry is that we have a 35-year record from nearly identical satellites flying almost the same ground track, with each mission overlapping the next,” Willis said. “That lets us look back in time and compare this El Niño to what happened in 1997. And right now, this one is on track to be even bigger.”

Compared with the 1997-98 event, El Niño in 2026 came on much more suddenly. But as of October, the two events appear similar in character—the tilt of sea level (low in the west and high in the east) and high, warm water extending all the way to South America—so Willis thinks the impacts could be similar as well. In 1997-98, that meant, for instance, lots of rain in California and across the southern tier of the U.S.

The 2015-16 El Niño was another heavy hitter but differed in its character. Sea surface height anomalies on October 12, 2015, based on altimetry data from the Jason-2 satellite, are shown above in context with maps from around the same time in 1997 and 2026. In 2015, the exceptionally warm, high water along the equator didn’t push up against South America to the extent it did in the other years. Rainfall impacts that winter concentrated more over Central America and the southeastern U.S., with significant flooding in Mexico.

NOAA’s El Niño outlook on October 8, 2026, called for an 83 percent chance of a strong-to-very strong El Niño through the first three months of 2027. But exactly how the impacts will play out in winter 2026-27 and beyond remains to be seen. Willis noted that El Niño's influence propagates through a chaotic atmosphere, and the signal can get muddled as it extends beyond the tropics. “There's always a bit of a dice roll here,” Willis said. “Just because this El Niño looks like 1997 doesn't mean it will be exactly the same—it's just our best guess at the moment.”

NASA Earth Observatory maps by Lauren Dauphin, using NASA-SSH altimetry data provided by Josh Willis, Severine Fournier, and Kevin Marlis, NASA/JPL-Caltech. Story by Kathryn Hansen.

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Full text from nasa.gov (public domain).