The Niño3.4 region of the central and eastern equatorial Pacific averaged 29.70°C (85.5°F) at the sea surface in September, an absolute monthly record, according to the Copernicus Climate Change Service. Copernicus said that reading exceeded the peak absolute temperatures measured during the strong El Niño events of 1982–83, 1997–98 and 2015–16.
The region is one of the main places scientists track El Niño, the warm phase of a natural Pacific climate cycle that can shift rainfall and temperature patterns around the world. The 2026 event formed in June and is still intensifying, so the September record arrived before forecasters expect it to peak.
A temperature record is not the whole ranking
Scientists do not judge El Niño strength only by the water’s absolute temperature. Human-driven warming has raised the background temperature of the oceans, making a direct comparison with older events less straightforward.
Copernicus director Carlo Buontempo told AFP that the event was exceptional but that it was too early to call it the strongest on record. The service has also adopted an index that adjusts for warming across the tropical oceans. On that relative measure, the current event had not yet surpassed every previous El Niño.
That distinction also explains why different agencies can describe the same event with different numbers. Absolute temperature measures how warm the water is. An anomaly measures how far it is above an expected baseline, while a relative index compares the El Niño region with the broader tropics.
NOAA expects more strengthening
In its Oct. 8 ENSO discussion, NOAA said the September monthly anomaly in Niño3.4 reached +2.1°C and that El Niño was likely to strengthen through the end of 2026.
NOAA gave an 83% chance that its three-month RONI value for October through December would reach at least +2.5°C, a level it said would make the event historically strong compared with El Niños dating to 1950. It also said a strong-to-very-strong event was likely to persist through January–March 2027.
A larger El Niño raises the odds of the rainfall and temperature shifts commonly associated with the pattern. NOAA cautioned that those effects are not guaranteed in any particular place, leaving the record-setting ocean reading as an important marker rather than a complete forecast.