El Niño Hits a Pacific Record on a Warmer Ocean

El Niño pushed the Niño 3.4 patch of the equatorial Pacific to 29.70°C (85.5°F) in September, the highest monthly reading in the Copernicus Climate Change Service record. That figure beat the peaks of the 1982/83, 1997/98 and 2015/16 events, and the present episode has not yet peaked.

The EU monitor still will not crown it the strongest El Niño on record. A newer index, built to strip out the warming of the wider tropics, says this is a very large event on a much warmer ocean, which is why 2026 and 2027 are both in play as record years.

The Pacific Box Hit 29.70°C Before the Peak

Copernicus, implemented by the European Centre for Medium-Range Weather Forecasts, said the monthly sea-surface temperature for the Niño 3.4 region reached an all-time high of 29.70°C in September. Those earlier very strong events all peaked between November and January. This reading arrived while the pattern was still building.

The September anomaly in the same box was also a record, at 2.99°C above the 1991-2020 average, above the previous mark of 2.81°C set in December 1997. Monthly temperatures sat more than 3°C above average across much of the central equatorial Pacific, including Niño 3.4.

The service posted the bulletin on October 12.

🌡 The latest C3S Climate Bulletin reports September was the 2nd-warmest on record, at 1.63°C above the estimated pre-industrial level. The average sea surface temperature across the extra-polar ocean reached a September record of 21.05°C. https://t.co/hPLo0JxSjT pic.twitter.com/3OckqKKhuW

— Copernicus ECMWF (@CopernicusECMWF) October 12, 2026

WHAT ELSE THE PACIFIC DID IN SEPTEMBER

• Extra-polar ocean: The 60°S to 60°N average was 21.05°C, the highest September on record, above 20.92°C in September 2023.
• All-time monthly mark: August still holds that, at 21.07°C, with September only a shade cooler.
• Daily streak: Since June 19, each calendar day’s extra-polar sea-surface temperature has been the highest recorded for that date.
• Eastern spike: Anomalies reached 6-7°C above average along the Peruvian coast and west of the Galápagos.

Carlo Buontempo, director of Copernicus, told AFP the episode is “very exceptional” and that it is too early to say whether it is the strongest ever observed. The last El Niño helped make 2024 the hottest year on record. This one emerged in June after Pacific warmth had already been building through spring.

Why Copernicus Still Will Not Call It the Strongest

Copernicus adopted a new yardstick that compares the central Pacific with the rest of the tropics at the same time, and on that scale the present event is not yet stronger than the classic Super El Niño years. Rising background ocean heat can make recent events look stronger than they were, which is why the service will not treat the 29.70°C reading as a simple historical knockout.

ECMWF released that Relative Niño index against tropical warming on June 8. Traditional Niño numbers compare a Pacific box with a fixed past baseline. As the whole tropical ocean warms, that older method folds climate change into the El Niño score. The relative version subtracts the tropics-wide anomaly so the leftover is closer to the oscillation itself.

Rising background temperatures can make recent El Niño events appear stronger than they are, and La Niña events seem weaker. The new Relative El Niño indices compare the Niño 3.4 and other regions with the overall temperature of the tropics at the same time, offering a perspective that is less sensitive to long-term warming.

Tim Stockdale, Principal Scientist, ECMWF

Buontempo put the same point in plainer terms: “It’s a very large event even in that metric. This very large event today is happening in a much warmer climate.” If the hottest Niño 3.4 water on record still does not settle the title, the extra heat is sitting in the rest of the tropical ocean. That gap is the climate-change signal inside the index, not a rounding error.

Stockdale added that even after the adjustment, forecasts still pointed to an unusually strong event later in 2026. Florian Pappenberger, Director-General of ECMWF, said at the June release that the centre could be looking at an event as significant as any in the past 50 years. Significance for weather is not the same as a raw temperature crown, and that is the split the September bulletin refused to blur.

Japan’s Gauge Is a Different Stretch of Ocean

The Japan Meteorological Agency does not wait on that relative scale. In its outlook covering October 2026 to April 2027, JMA said El Niño conditions, present since spring, have reached their strongest intensity on record since September.

JMA tracks NINO.3, a box that sits farther east than Niño 3.4, from 150°W to 90°W between 5°N and 5°S. In September the NINO.3 sea-surface temperature was +4.0°C above normal. That beat the previous record of +3.6°C set in December 1997, the highest in a series that starts in 1949.

The agency said the strongest conditions are virtually certain (100%) to continue until Northern Hemisphere winter, and that NINO.3 is expected to rise further, with a record peak likely in that season. The five-month running mean for July was +2.6°C, the fourth straight month above JMA’s El Niño threshold. Subsurface water was far above normal in the central and eastern equatorial Pacific, and trade winds over the central Pacific were much weaker than normal.

SEPTEMBER WEATHER THAT MATCHED PAST EL NIÑO YEARS

• Heat belt: Above-normal temperatures from the southern Philippines to Java, from northern South America to the tropical central Pacific, and from eastern to southwestern Australia.
• Cool pockets: Below-normal temperatures in southern South America and southern Polynesia.
• Rain shift: Above-normal rain in southern Argentina; below-normal rain in northern South America, from southwestern Polynesia to northern Australia, and in southeastern Southeast Asia.
• Japan winter: JMA said the pattern could bring a warmer-than-usual winter, with more rain than usual on the Pacific side of eastern Japan and in the Okinawa-Amami region.

The Indian Ocean was above normal in September, and JMA’s Dipole Mode Index stood at +0.69, with the western tropical Indian Ocean especially warm. That is a separate pattern, but it is running at the same time as the Pacific event, which is how a “Pacific story” starts leaking into African and Australian rainfall as well.

NOAA Puts a Historic Mark on Odds, Not on the Books

The U.S. Climate Prediction Center, in its October 8 diagnostic, is closer to Copernicus than to Tokyo on the title fight. CPC now scores El Niño on relative sea-surface temperatures, Niño 3.4 minus the tropical mean from 20°N to 20°S, then rescales the result so the old thresholds still make sense.

Most of those relative indices rose in September, reaching +2.1°C in Niño 3.4, +3.0°C in Niño 3, and +3.9°C in Niño 1+2. Patches of the eastern equatorial Pacific exceeded +4.0°C. The subsurface, averaged from 180° to 100°W, stayed well above average, with temperatures still in excess of +10.0°C at depth in the east. Convection stayed enhanced from the central to eastern Pacific and suppressed over Indonesia, and the Southern Oscillation indices were strongly negative.

Historic, in CPC’s language, means a three-month Relative Oceanic Niño Index of +2.5°C or more, a bar that would exceed every El Niño in its record back to 1950. The centre gave an 83% chance of a historic event for October-December, with 54% for September-November and 70% for November-January. A strong-to-very strong event remains likely through January-March 2027, still above an 83% chance. The next diagnostic is due on November 12.

THREE AGENCIES, THREE SEPTEMBER READINGS

None of those rows is a correction of the others. They are different boxes, different baselines, and in NOAA’s case a different subtraction. The wire-story habit of collapsing them into “strongest ever” is what the relative index was built to stop.

The Ocean Feeding This Event Is the Warmest Measured

Celeste Saulo, Secretary-General of the World Meteorological Organization, told the Global Heat Forum in Bangkok on October 6 that El Niño does not add new heat to the planet. It releases heat the ocean has already stored. The eleven years from 2015 to 2025 were the eleven warmest humanity has recorded, she said, and the ocean set a new heat record for the ninth year running in 2025.

The ocean it’s drawing from is the warmest we’ve ever measured it. There is simply more heat available to release.

Celeste Saulo, Secretary-General, World Meteorological Organization

WMO’s Global Seasonal Climate Update said the Niño 3.4 anomaly rose from +1.6°C above normal in June to +2.5°C in August. For October-December the seasonal average is forecast to reach about 3.7°C above normal, peaking around December, with a near-100% likelihood that El Niño persists through February 2027. Saulo called it “one of the strongest since at least 1950.”

That forecast and Copernicus’s relative caution can both be true. WMO is describing a Pacific that is about to dump stored heat into the air. Copernicus is describing an oscillation whose own amplitude, once the tropical background is removed, has not yet cleared 1982, 1997 or 2015. The weather still changes. Drought, flood and fire risk still rise. The title on the event is the part that depends on which ruler you pick.

Buontempo, speaking to AFP, kept the cause in view: while El Niño plays a role, “the ultimate cause of the rise and the exceedance of 1.5°C is anthropogenic emissions of greenhouse gases.”

A Second Month Above the 1.5°C Line

September’s global surface air temperature was 16.27°C, 0.82°C above the 1991-2020 average, which made it the second-warmest September in the ERA5 dataset and 0.11°C cooler than September 2023. It was 1.63°C above the 1850-1900 preindustrial average, the second straight month above 1.5°C after August. The last month before August to clear that line was November 2025.

A month above 1.5°C is not a breach of the Paris Agreement, which is a long-term average. The 12-month mean from October 2025 to September 2026 was 1.50°C above 1850-1900, the first time that running average has sat at 1.50°C since October 2025. Nations agreed in Paris in 2015 to keep warming well below 2°C and to pursue 1.5°C. The United Nations said in September that the long-term 1.5°C target would be missed in a matter of years.

Global land in September averaged 13.67°C, behind the 14.10°C record from September 2023. Europe’s land average was 16.26°C, 1.54°C above 1991-2020, the third-warmest September there and 0.97°C behind 2023. Western Europe tied September 2023 as its joint warmest, at 2.51°C above average. Portugal had its warmest September on record, and France and Ireland their second warmest, on preliminary national figures cited by Copernicus. West Antarctica ran 10-15°C above average, a classic El Niño teleconnection via high pressure over the Amundsen Sea.

HOW THE 2026 EVENT HAS BUILT

1. June 2, 2026: WMO announces El Niño conditions are under way in the equatorial Pacific.
2. June 19, 2026: Daily extra-polar sea-surface temperatures become the highest on record for each calendar day, a streak Copernicus said was still intact through September.
3. August 2026: A new run of months more than 1.5°C above 1850-1900 begins. Extra-polar SST hits an all-time monthly mark of 21.07°C.
4. September 2026: JMA’s NINO.3 anomaly hits +4.0°C. Global air finishes 1.63°C above preindustrial, the second month of the new 1.5°C run.
5. October 8-12, 2026: NOAA posts 83% odds of a historic October-December RONI. JMA calls its index the strongest since 1949. Copernicus publishes the Niño 3.4 monthly SST record and still withholds the strongest-ever label.

Buontempo said the new run of months above 1.5°C, with a strong El Niño still intensifying, is likely to last into 2027. “Crossing the Paris Agreement’s long-term limit is only a matter of time. How far we overshoot, and for how long, is still up to us.”

Could 2026 Be the Hottest Year on Record?

From January through September, 2026 ranks as the second-warmest year on record, behind 2024 and ahead of 2023 and 2025. That ranking is a poor guide to the finish, Copernicus warned, because the last El Niño of this strength, in 2023, produced a sharp rise in global anomalies in the final months. The present event is already stronger than 2023 at the same stage and is forecast to strengthen further by the end of 2026.

If the last three months of 2026 are as warm as they were in 2023, Copernicus said the annual average would sit close to 2024, the current hottest year. Buontempo went further on the lag that follows a big Pacific event: “If we follow the pattern we have seen in the past, we may have a record-breaking 2026, followed by a record-breaking 2027.” El Niño typically arrives every two to seven years and lasts about nine to 12 months, and it often lifts global temperature most in the year after its peak as stored Pacific heat leaks into the air.

WMO has the event persisting through February 2027. JMA has record-strength conditions continuing through winter. NOAA has a strong-to-very strong El Niño likely through January-March 2027. Those are duration forecasts, not a verdict on the calendar-year trophy, and they can all verify while the relative index still refuses the “strongest ever” stamp.

The Niño 3.4 water is already hotter than it was at the peak of the last three Super El Niño years. The relative index says the oscillation has not yet outrun those years. The practical result is the same either way: a large Pacific event is unloading heat from the warmest ocean in the instrumental record, and the 1.5°C monthly run that started in August is the early receipt.