Satellite sea-level data show warm Pacific water building rapidly, while forecasters expect record-strength conditions and uncertain regional weather impacts

NASA satellite measurements indicate that the El Niño developing in 2026 closely resembles the powerful 1997–98 event — and may ultimately exceed it.

On 23 October 2026, the agency’s Earth Observatory had published side-by-side sea-surface-height maps comparing October 13, 1997, with October 12, 2026. Because seawater expands as it warms, higher-than-normal sea levels in the central and eastern equatorial Pacific reveal accumulating El Niño-related heat.

The 1997 observations came from TOPEX/Poseidon, while the 2026 data came from Sentinel-6 Michael Freilich; scientists at NASA’s Jet Propulsion Laboratory (JPL) had processed both datasets.

Josh Willis, project scientist for sea level missions at JPL, said the value of satellite altimetry lies in its 35-year record from closely matched satellites flying nearly identical paths. That continuity allows researchers to compare 2026 directly with 1997, and he said the current event is “on track to be even bigger.”

Detailed data comparisons

Notably, the 2026 event had developed much more rapidly than the 1997–98 episode. By October, however, both showed a similar structure: sea level lower in the western Pacific and higher in the east, with warm, elevated water extending to South America. Willis suggested the weather effects could therefore be comparable.

The 2015-16 El Niño was also exceptionally strong, but it had differed in shape. Its warmest water and highest sea levels had stayed farther offshore, and its heaviest rainfall had affected Central America, Mexico, and the south-eastern United States.

NASA Earthdata reported that the 2026 event began late and initially lagged behind both 1997 and 2015 at the same point in the season. Eastward wind bursts during the summer then produced new Kelvin waves — subsurface ocean pulses that helped the event intensify and catch up.

Forecasts concur on possible superlatives

Forecasters increasingly describe the event as potentially historic:

  • NOAA’s Climate Prediction Center had said on 8 October 2026 that a strong-to-very strong El Niño is likely through January–March 2027, with greater than an 83% chance. It had also assigned an 83% probability that October–December conditions would surpass every El Niño in records dating to 1950.
  • Columbia University’s International Research Institute has reported that the weekly Niño 3.4 index, centered on 14 October 206, had reached +3.3°C. All 27 models in its mid-October ensemble forecast a “very strong” El Niño from October–December 2026 through December–February 2026–27.
  • The World Meteorological Organization expects central Pacific temperatures to rise about 3.8°C above normal from November through January, peaking around December. Secretary-General Celeste Saulo has said the projection exceeds values of roughly 3°C seen in earlier record events.

Nevertheless, Willis has urged caution about translating ocean conditions into specific regional outcomes. El Niño’s influence must pass through a chaotic atmosphere, and its signal can become less distinct outside the tropics. “There’s always a bit of a dice roll here,” he said, adding that the resemblance to 1997 is the best available guide rather than a guarantee of identical impacts.