Sea levels across the central and eastern equatorial Pacific are higher than normal this month, a hallmark of El Niño, and the pattern closely resembles October 1997, during one of the strongest events in the satellite record, NASA's Earth Observatory reports.
The comparison is made through sea surface height. Because water expands as it warms, higher-than-normal sea levels in that part of the Pacific signal the buildup of heat associated with El Niño. The published maps show 13 October 1997 from the TOPEX/Poseidon satellite and 12 October 2026 from Sentinel-6 Michael Freilich, with 12 October 2015 from Jason-2 for comparison.
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 events, in 1997-98 and 2015-16, upended weather patterns worldwide, from fires in Indonesia and the Amazon to crop failures from drought in southern Africa and heavy rain and coastal flooding in southern California.
Each event 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. "They're all different in terms of where they land and how their impacts play out."
"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."
This year's event arrived much more suddenly than the 1997-98 one. But as of October the two look similar in character, with sea level tilted low in the west and high in the east and warm water extending all the way to South America, so Willis thinks the impacts could be similar too. In 1997-98 that meant a great deal of rain in California and across the southern tier of the United States.
The 2015-16 event was another heavy hitter but differed in its character. Less of the elevated water reached the coast of South America, and rainfall that winter concentrated more over Central America and the south-eastern United States, with significant flooding in Mexico.
NOAA's El Niño outlook on 8 October called for an 83 per cent chance of a strong-to-very-strong El Niño through the first three months of 2027. Willis noted that the influence propagates through a chaotic atmosphere and the signal can get muddled beyond the tropics. "There's always a bit of a dice roll here," he 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."
The maps were made by NASA Earth Observatory's Lauren Dauphin using altimetry data provided by scientists at the Jet Propulsion Laboratory, with the story written by Kathryn Hansen.
What has been assembled here deserves to be appreciated on its own terms: a measuring instrument of remarkable consistency, pointed at a phenomenon of remarkable inconsistency. Thirty-five years, a succession of nearly identical satellites, almost the same ground track, each mission overlapping the next, in order to establish that the search for the typical El Niño is very elusive.
The record now holds three very strong events. Two of them look alike and behaved differently. The third looks different and is expected to behave like one of the first two. Our analysts observe that this exhausts the available combinations.
The Department of Unnecessary Research notes that the sample size is three, the population is one ocean, and the ocean has been observed doing something unprecedented and familiar at the same time. No further instruments are required to reach this result, and none would help.
There is nothing wrong with any of it. It is simply the unusual case of a measurement so precise that it has established, to the centimetre, the exact shape of not knowing.
After thirty-five years of continuous observation the Pacific can at last be compared with itself in detail, and the finding is that it declines to be.