El Niño Then and Now
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A 35-year satellite altimetry record lets scientists hold this year’s El Niño up against its strongest predecessors.
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Summary
NASA’s Earth Observatory has released satellite data comparing the current El Niño event in October 2026 with the strong events of 1997 and 2015. Altimetry maps show that sea levels in the central and eastern equatorial Pacific are significantly higher than normal in 2026, a pattern that closely mirrors the conditions observed in October 1997. This similarity suggests the current event may have a similar character and potential impact to the 1997-98 El Niño, which was one of the strongest on record. In contrast, the 2015-16 El Niño, while also very strong, exhibited a different pattern where warm water did not extend as far toward the South American coast, resulting in distinct weather outcomes such as concentrated rainfall in Central America and the southeastern United States. The mechanism behind El Niño involves a feedback loop where weakened trade winds allow warm water to move eastward, further weakening the winds and intensifying the warming. Satellite altimetry detects this by measuring sea surface height, as warmer water expands and rises. Josh Willis, a project scientist at NASA’s Jet Propulsion Laboratory, highlighted that the 35-year record from nearly identical satellites allows scientists to make precise historical comparisons. Although the 2026 event developed more rapidly than the 1997 event, the current sea level tilt and warm water distribution indicate it is on track to be significant. NOAA currently forecasts an 83 percent chance of a strong-to-very strong El Niño through early 2027. However, because El Niño signals propagate through a chaotic atmosphere, the exact global weather impacts for the coming winter remain subject to variability, with Willis noting that while 1997 is the best model for prediction, it is not a guarantee of identical outcomes.
Key points
- NASA satellite altimetry data from October 2026 shows sea levels in the central and eastern equatorial Pacific are higher than normal, a hallmark of El Niño.
- The sea surface height pattern in October 2026 closely resembles that of October 1997, one of the strongest El Niño events in the 35-year satellite record.
- While the 2026 event developed more suddenly than the 1997-98 event, the current tilt of sea level and warm water extending to South America suggest similar potential impacts.
- The 2015-16 El Niño, also very strong, differed in character because elevated warm water did not reach the South American coast as extensively, leading to different rainfall patterns.
- Altimetry satellites measure sea surface height to track El Niño, as warmer water expands and raises sea levels in affected regions.
- Josh Willis of NASA JPL noted that the 35-year record from overlapping satellite missions allows for direct comparisons between current and past events.
- NOAA's October 8, 2026, outlook predicts an 83 percent chance of a strong-to-very strong El Niño persisting through the first three months of 2027.
- Despite similarities to 1997, atmospheric chaos means the exact global weather impacts for winter 2026-27 remain uncertain.
Context and interpretation
The current El Niño is being tracked as a potential 'heavyweight' event comparable to the severe 1997-98 and 2015-16 episodes, which caused global disruptions including droughts, fires, and flooding. The ability to compare 2026 data directly with 1997 and 2015 using a consistent 35-year satellite record provides a critical baseline for forecasting the severity and geographic distribution of upcoming weather impacts, although atmospheric variability still introduces uncertainty.
Source: NASA
