CPC's 10 September Read: 75% Chance El Niño Exceeds Every Event Since 1950

NOAA's Climate Prediction Center (CPC) said in its monthly ENSO Diagnostic Discussion, issued 10 September 2026, that El Niño strengthened further over the past month and that there is a greater than 90% chance of a very strong event during the Northern Hemisphere fall and winter of 2026-27. The centre kept its ENSO Alert System Status at El Niño Advisory.

The index values the CPC reported

The CPC said sea surface temperature anomalies exceeded +3.0°C in the eastern equatorial Pacific. Among the monitoring regions, the centre reported Niño-3.4 at +1.8°C, Niño-3 at +2.5°C and Niño-1+2 at +3.4°C, all having increased. The exception was the Niño-4 index, which the CPC said decreased to +0.1°C in August.

A point of care for readers comparing these numbers with the forecast further down the discussion: the CPC ties the Niño-4 figure explicitly to August but does not spell out in the text of the discussion the averaging window applied to the other regional values. The seasonal threshold quoted later in the same document is stated on a different basis again — a three-month value of the relative oceanic Niño index (RONI). The two sets of figures are therefore not directly interchangeable.

Below the surface, the CPC reported that its equatorial subsurface temperature index, an average from 180°-100°W, remained steady during August, reflecting a deeper-than-average thermocline, and that subsurface temperatures continued to be significantly above average.

Atmospheric signals

The CPC described low-level westerly wind anomalies and upper-level easterly wind anomalies extending from the western to the east-central equatorial Pacific. Enhanced convection and rainfall persisted from the central to the eastern Pacific, the centre said, while anomalies remained suppressed over Indonesia. Both the traditional and equatorial Southern Oscillation indices stayed negative. Taken together, the CPC concluded, the coupled ocean-atmosphere system reflected a strengthening El Niño.

That combination — surface westerly anomalies, easterly anomalies aloft, and rainfall displaced eastward away from the Indonesian region — is the pattern forecasters look for when judging whether an oceanic warm anomaly has coupled with the overlying circulation rather than remaining a sea-surface signal alone. Background on the mechanism is on our science pages.

Two labels, one defined threshold

The CPC Official ENSO outlook, which the centre says synthesizes multiple models from North America and abroad, indicates El Niño will continue to strengthen through the end of the year. For the October-December 2026 season, the CPC placed a 75% chance on a historic event that would exceed the strength of previous El Niño events dating back to 1950 — a category the discussion defines numerically as a 3-month RONI value of +2.5°C or more.

The centre's other label carries no stated numerical test in this document. The phrase "very strong event," used in the CPC's synopsis and repeated in its closing summary alongside the greater than 90% probability, is not accompanied in the discussion text by the index or threshold the centre applies to it. Only the "historic" category is quantified, and it is quantified in RONI rather than in the Niño-region sea surface temperature values listed earlier. Readers should treat the two as distinct claims made on distinct measures.

The CPC also attached a caveat to the forecast magnitude: with an event of this size, it said, the chances of experiencing impacts consistent with El Niño are larger, though not guaranteed, and it pointed to its own outlooks for the probabilities of seasonal anomalies. Both figures are forecast probabilities, not observations.

Next update

The discussion is described by the CPC as a consolidated effort of the National Oceanic and Atmospheric Administration, NOAA's National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center website, and the centre notes that a probabilistic strength forecast is published separately. The next ENSO Diagnostics Discussion is scheduled for 8 October 2026. Successive updates are tracked in our news archive, and the Niño regions and RONI are explained in the glossary.