The monthly sea-surface temperature of the Niño 3.4 region of the equatorial Pacific reached 29.70 degrees Celsius (29.70C) in September 2026, the highest value ever recorded for that index. The figure comes from the Copernicus Climate Change Service, the European Union’s climate monitor, and it sits above the peaks of three of the most powerful El Niño events on record.
The 29.70 figure is easy to misread, so the details matter: it is a one-month average for one box of ocean, not a global temperature and not a measure of how strong the El Niño is. The sections below separate what the number measures, what the comparison with earlier events does and does not establish, and what NOAA’s forecast says is coming.
The Niño 3.4 box and the ERA5 data behind 29.70 degrees
Niño 3.4 is a rectangle of the central equatorial Pacific that forecasters watch because warm water there shifts rainfall and the jet stream across the globe. Copernicus describes it as the ocean region used to monitor El Niño conditions, and its bulletin states that the monthly sea-surface temperature for the region “reached an all-time high of 29.70°C in September,” exceeding the peak values of the 1982/1983, 1997/1998 and 2015/2016 events, according to the Copernicus September 2026 climate bulletin.
The scope of that sentence is narrow. The value is a monthly mean for September 2026, not a weekly reading, and weekly and monthly averages of the same ocean can differ by several tenths of a degree. The bulletin draws its sea-surface figures from ERA5, the reanalysis in the Copernicus ERA5 monthly means dataset, which estimates ocean temperature at roughly 10 metres depth.
Other agencies compute the same box with different datasets, depths and base periods, so a 29.70 reading from Copernicus should not be compared directly with a figure from another provider without checking which product produced it.
What beating 1982, 1997 and 2015 does and does not establish
Copernicus compares the September value with the peaks of three events: the 1982/1983 El Niño, the 1997/1998 El Niño and the 2015/2016 El Niño. In each case the comparison is of the highest monthly Niño 3.4 sea-surface temperature reached during that event against the September 2026 monthly value. All three are the benchmark very strong events in the modern record, which is why the bulletin treats surpassing them as notable.
What the comparison does not establish is that 2026 is the strongest El Niño ever. El Niño is defined by an anomaly, meaning how far the region runs above a long-term baseline, and not by an absolute temperature. A box that is warm in absolute terms can be a modest El Niño if the baseline is also warm, and the long-term warming of the tropical oceans means that each new event starts from a higher floor than the 1982 one did. A record absolute reading is therefore a strong hint, but the verdict belongs to the anomaly figures.
The anomaly figures come from NOAA. In its 8 October 2026 discussion, the Climate Prediction Center reported that Niño indices increased over the past month, reaching +2.1°C in Niño 3.4, +3.0°C in Niño 3 and +3.9°C in Niño 1+2, according to the NOAA Climate Prediction Center ENSO discussion. Strong by that yardstick, but the center’s threshold for a historic event is a three-month relative index of +2.5°C or more, which has not yet been reached.
NOAA’s 83 percent odds and the winter outlook
The forecast side of the story is also NOAA’s. The Climate Prediction Center keeps an El Niño Advisory in place and says El Niño continues to strengthen, with a strong-to-very-strong event likely through January to March 2027. It puts the chance of a historic event, one that would exceed previous El Niño events dating back to 1950, at 83 percent for October to December. The same discussion gives 54 percent for September to November and 70 percent for November to January, so the probability peaks in the current season rather than climbing steadily.
The percentages are forecast odds for a three-month season, not a statement that a historic event is already underway. The distinction matters for the record-setting temperature: the Copernicus number describes September, while NOAA’s 83 percent describes what the ocean and atmosphere may do over the coming months.
Carlo Buontempo, director of the Copernicus Climate Change Service, said the world is in a new run of months above 1.5 degrees Celsius and that, with a strong El Niño still intensifying, the run is likely to last into 2027. His point links the Pacific box to the global thermometer: El Niño tends to add heat to the atmosphere with a lag, so the warmest consequences often arrive after the ocean peak.
For readers asking what kind of winter this means, the honest answer is that the discussion points elsewhere. NOAA’s diagnostic text does not give a temperature or precipitation forecast; it refers readers to the center’s seasonal outlooks. Background on how the tropical Pacific steers winter patterns is laid out on NOAA’s ENSO resource page, and the historical record of strong events is tabulated in the Oceanic Niño Index table, which is the standard way past events are ranked by anomaly.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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