NASA’s Earth Observatory published a side-by-side comparison on Oct. 23 of the Pacific Ocean in three different Octobers: 1997, 2015 and 2026. A 35-year satellite altimetry record, it says, lets scientists hold this year’s El Niño up against its strongest predecessors, and the comparison shows an event that rivals the very strong episodes of 1997-98 and 2015-16.
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The maps track sea surface height, a measure of how much heat the upper ocean is storing, and they were drawn from three different satellites flown in three different decades. Josh Willis, a project scientist for sea level missions at NASA’s Jet Propulsion Laboratory, supplied the interpretation, along with a caution about how far the resemblance should be pushed.
Three satellites, three Octobers
The comparison depends on a chain of spacecraft. The 1997 map uses data from TOPEX/Poseidon for Oct. 13, 1997. The 2015 map uses Jason-2 data for Oct. 12, 2015, and the 2026 map comes from Sentinel-6 Michael Freilich on Oct. 12, 2026. NASA’s El Niño Then and Now shows the anomalies after seasonal cycles and long-term trends are removed, so the colors show how far the ocean sits from its usual state.
The physics is simple. Warm water expands, so higher-than-normal sea levels in the central and eastern equatorial Pacific signal stored heat. The data credited to the maps are the NASA-SSH sea surface height records assembled by Willis, Severine Fournier and Kevin Marlis of NASA’s Jet Propulsion Laboratory, with maps by Lauren Dauphin and a story by Kathryn Hansen.
1997 as the closest match, 2015 as the outlier
The closest resemblance is to 1997. As of October, according to the Earth Observatory, the two years look similar: sea level is tilted, low in the western Pacific and high in the east, and warm, high water extends all the way to South America. The one clear difference is speed. The 2026 event arrived much more suddenly than the one in 1997.
Willis said the impacts could turn out similar as well. In 1997-98, those impacts included heavy rain in California and the southern United States. The 2015 event looks different on the map, because less elevated water reached South America, and the rain that winter concentrated over Central America and the southeastern United States, with significant flooding in Mexico. Each strong El Niño has therefore delivered its own regional pattern of wet and dry, so the comparison lays three maps next to one another instead of treating any one year as the template.
NOAA’s odds and the limits of a look-alike
The Climate Prediction Center put numbers on the outlook in its Oct. 8 diagnostic discussion. It called for “a strong-to-very strong El Niño likely through January-March 2027,” and gave the chance of a historic event, defined as a three-month relative index of +2.5 degrees Celsius or higher, as 54% for September-November, 83% for October-December and 70% for November-January. NASA’s own summary of the outlook cites the 83% figure.
Willis was careful about what a matching map can and cannot say. The signal can get muddled in the chaotic atmosphere, he cautioned, and “Just because this El Niño looks like 1997 doesn’t mean it will be exactly the same.” A look-alike ocean raises the odds of familiar impacts, but the weather that reaches any single city depends on how the atmosphere responds in a given month.
What the sea-level numbers add
A separate NASA report from Oct. 15, NASA Satellites Observe Historic 2026 El Niño, gives the measurements behind the picture. Local sea levels rose by as much as 1 to 1.3 feet (30 to 40 centimeters) in some areas, while levels 6 to 8 inches (15 to 20 centimeters) below normal appeared around Indonesia and northern Australia. Altimetry records have been kept since 1993, and Sentinel-6 measures ocean height across the whole ocean every 10 days.
The same report traces how the event began. A Kelvin wave was spotted near Micronesia in January 2026, and by early April those waves had reached the eastern Pacific, where sea surface temperatures began to warm. Willis described Kelvin waves as “like the heartbeat of El Niño.” The report also notes that equatorial Pacific waters have become measurably bluer over recent months as phytoplankton decline, an expected effect of El Niño that NASA’s PACE satellite, launched in 2024 and observing its first El Niño, can detect from orbit. Matthew Kehrli, lead research scientist for the PACE team at NASA’s Goddard Space Flight Center, said that seeing the results in real time is gratifying. NASA adds that eastern Pacific sea surface temperatures were about 3 degrees Fahrenheit (1.7 degrees Celsius) above the long-term average when that report was written.
For readers who want the raw record, NASA’s Jet Propulsion Laboratory maintains the El Niño 2026 sea level page, and the mission sheet for Sentinel-6 describes the spacecraft that produced this year’s map.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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