NOAA raises chance of historic-strength El Niño to 75% for October–December 2026
The Climate Prediction Center (CPC) raised the probability of a historic-strength El Niño during October–December 2026 to 75% on September 10, 2026, up from 69% in August, after the coupled ocean-atmosphere event strengthened further across the tropical Pacific. CPC also raised the probability of a very strong event during the same three-month period from 95% to 98%.
NOAA coral reef watch 5km sst anomalies-September 9, 2026 shows the strengthening El Nino. Credit: NOAA/NESDIS
Sea surface temperature anomalies exceeded +3°C (+5.4°F) across the eastern equatorial Pacific during August. Niño-3.4 increased to +1.8°C (+3.2°F), Niño-3 reached +2.5°C (+4.5°F) and Niño-1+2 rose to +3.4°C (+6.1°F), while Niño-4 decreased to +0.1°C (+0.2°F).
CPC said the combined oceanic and atmospheric conditions reflected a strengthening El Niño.
The August measurements reported in CPC’s September 10 assessment represent a further increase from July, when anomalies stood at +1.4°C (+2.5°F) in Niño-3.4, +1.7°C (+3.1°F) in Niño-3 and +2.9°C (+5.2°F) in Niño-1+2.
CPC’s August assessment assigned a 69% probability that the October–December three-month Relative Oceanic Niño Index (RONI) would reach at least +2.5°C (+4.5°F). The September update increased that probability by 6 percentage points.
CPC describes an October–December RONI of +2.5°C (+4.5°F) or higher as a historic event because it would exceed the strength of previous El Niño events in its record dating to 1950. The 75% probability represents a forecast and does not mean that a record-strength event has already occurred.
The updated assessment advances the outlook covered by The Watchers on August 17, when CPC placed the historic-event probability at 69% and the chance of a very strong October–December event at 95%.
CPC’s strength categories use a lower threshold for a very strong event. Its September forecast gives a 98% probability that the October–December RONI will reach at least +2°C (+3.6°F), up 3 percentage points from August.
The probability of a very strong event is 93% for November 2026–January 2027 and 75% for December 2026–February 2027. It then falls to 39% for January–March 2027 and 5% for February–April.
Warmth continued well below the Pacific surface. CPC reported that the equatorial subsurface temperature index, averaged between 180° and 100°W, remained steady during August as the thermocline stayed deeper than average. Widespread subsurface temperature anomalies exceeded +10°C (+18°F) at depth.
Atmospheric conditions remained coupled with the anomalously warm ocean. Low-level westerly wind anomalies and upper-level easterly wind anomalies extended from the western to east-central equatorial Pacific.
Convection and rainfall remained enhanced from the central to eastern Pacific and suppressed over Indonesia. The traditional and equatorial Southern Oscillation indices also remained negative.
CPC expects El Niño to continue strengthening through the end of 2026 and has maintained its El Niño Advisory. The agency summarized the outlook as carrying a greater than 90% chance of a very strong event during Northern Hemisphere fall and winter 2026–27.
The forecast does not mean that regional impacts will increase in direct proportion to the RONI value. CPC said stronger El Niño events tend to increase confidence in some characteristic impacts but do not guarantee a particular temperature or precipitation outcome in any location.
References:
1 ENSO Diagnostic Discussion – CPC/NCEP/NWS – September 10, 2026
2 Official NOAA CPC ENSO Strength Probabilities – NOAA/CPC – issued September 2026
Rishav Kothari is Editor-in-Chief of The Watchers, where he runs the newsroom and covers earthquakes, volcanoes, severe weather and space weather.
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