NASA satellites show this year's El Niño tracking ahead of the 1997 giant

The El Niño building across the Pacific this fall is keeping pace with the 1997-98 event, one of the most powerful on record, and may surpass it. NASA scientists reached that view by comparing satellite measurements of sea level taken almost three decades apart.

"And right now, this one is on track to be even bigger," said Josh Willis, project scientist for sea level missions at NASA's Jet Propulsion Laboratory. He paired that assessment with a caution that matters as much as the headline comparison: an El Niño that looks like 1997 in the ocean will not necessarily deliver 1997's weather on land.

The federal forecast points the same direction. In its Oct. 8 outlook, the National Oceanic and Atmospheric Administration put the odds at 83 percent that strong to very strong El Niño conditions will be in place from January through March 2027. When a long-running satellite record and NOAA's probabilities line up this closely, the strength of the event looks well established. What remains open is where its effects will land.

Reading heat from the height of the sea

The comparison rests on satellite altimetry, which tracks small rises and dips in the ocean surface. Warmer seawater expands, so a sea surface sitting unusually high in the central and eastern equatorial Pacific marks where El Niño's heat is collecting.

JPL researchers set two maps side by side. The first shows Oct. 13, 1997, measured by the TOPEX/Poseidon satellite. The second shows Oct. 12, 2026, from Sentinel-6 Michael Freilich. The team processed both datasets the same way and stripped out seasonal swings and long-term trends, so what remains reflects El Niño and other short-lived natural variation. Red marks water above its usual level, white is normal, and blue is below average.

The comparison carries weight because of the record behind it. Each altimetry mission has flown nearly the same ground track as the one before, and each overlapped its predecessor in orbit. "What's unique about altimetry is that we have a 35-year record from nearly identical satellites," Willis said. Many climate datasets mix instruments and methods over time. This one gives scientists an unusually direct comparison across decades.

By that measure, the 2026 event stands out. It strengthened far more abruptly than the 1997-98 episode did. By October, though, the two maps had converged. Both show the Pacific tilted, with sea level low in the west and high in the east. Both also show a ridge of elevated, unusually warm water running east along the equator all the way to the coast of South America.

That eastward spread follows the basic mechanics of El Niño. Normally, steady trade winds push warm surface water west, where it piles up and leaves the western Pacific slightly higher than the east. When those winds slacken, warm water drifts back east. That can weaken the winds further or even reverse them, which lets still more warm water move east. The loop feeds on itself, raising ocean temperatures and sea levels across the central and eastern basin. The cycle typically recurs every two to seven years. The rapid buildup this year suggests the feedback took hold quickly, which leaves less lead time than in 1997 for anyone planning around the coming winter.

Why 2015 is the cautionary case

The 1997-98 El Niño brought heavy rain to California and other parts of the southern United States, and NASA says the current resemblance raises the possibility of similar conditions this winter. Strong events carry consequences well beyond the U.S. Both the 1997-98 episode and the 2015-16 event brought destructive fires in Indonesia and the Amazon, severe drought and crop failures in southern Africa, and intense rainfall and coastal flooding in Southern California.

The 2015-16 event is the reason scientists are hedging. Measured by overall strength, it belonged in the same class as 1997. For comparison, the JPL team pulled Jason-2 satellite data from Oct. 12, 2015, roughly the same point in the season. The equator again showed exceptionally warm water and high sea levels. But that warmth did not push toward South America's coast as strongly as it did in 1997 or does now.

The weather that followed had a different shape. Much of the El Niño-related precipitation that winter fell over Central America and the southeastern United States, and Mexico saw significant flooding. The lesson is that the location of the warm water can matter as much as the amount. On that point, this year's map looks more like 1997 than 2015, which is the strongest reason behind NASA's comparison.

Even that resemblance has limits. El Niño reshapes weather around the world by shifting how heat and moisture move through the atmosphere. The farther a region sits from the tropical Pacific, the more other atmospheric processes can bend or blunt the expected pattern. NOAA's 83 percent figure speaks to the strength of the event, not to which coastlines or farm belts will take the brunt.

"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." He called the comparison the team's best guess at the moment, and that is an honest description of where the science stands.

"The search for the 'typical' El Niño is very elusive," Willis said, noting that the events differ in where they land and how their impacts play out. The thing to watch over the next few months is whether the warm water keeps hugging the South American coast, as it did in 1997, or retreats toward the central Pacific, as it did in 2015. That will be the clearest sign yet of which historical winter this one resembles.