October ENSO Discussion: CPC Logs Niño-3 at +3.0 °C, Advisory Unchanged

NOAA's Climate Prediction Center left its ENSO Alert System Status at El Niño Advisory in the monthly ENSO Diagnostic Discussion issued on 8 October 2026, reporting that the event grew stronger over the past month across both the ocean and the atmosphere.

The agency's synopsis reads: "El Niño continues to strengthen, with a strong-to-very strong El Niño likely through January-March 2027 (remaining greater than an 83% chance)."

What the CPC observed last month

Most of the monitored Niño regions rose over the month, according to the CPC. The agency listed +2.1 °C in Niño-3.4, +3.0 °C in Niño-3 and +3.9 °C in Niño-1+2, the easternmost region nearest the South American coast. The discussion also reported sea surface temperature anomalies exceeding +4.0 °C in portions of the eastern equatorial Pacific, pointing readers to Figure 1 of the product; the text does not specify the longitude band over which that maximum was reached.

Below the surface, the CPC said its equatorial subsurface temperature index — the average taken between 180° and 100°W — was well above average, which the agency linked to a deeper-than-average thermocline. Subsurface temperatures remained in excess of +10.0 °C at depth in the eastern Pacific Ocean, the discussion stated, citing Figure 4; again, the prose does not give the depth at which that anomaly was found.

The atmospheric signature was consistent with the ocean state. The CPC described low-level westerly wind anomalies and upper-level easterly wind anomalies stretching from the western to the east-central equatorial Pacific, with enhanced convection and rainfall persisting from the central to the eastern Pacific while anomalies stayed suppressed over Indonesia. Both the traditional and equatorial Southern Oscillation indices were significantly negative. Collectively, the agency concluded, the coupled ocean-atmosphere system reflected a strengthening El Niño.

The RONI threshold and its seasonal odds

The CPC Official ENSO outlook, which the agency says synthesises multiple models from North America and abroad, indicates El Niño will continue to strengthen through the end of the year.

The discussion then attaches numbers to a specific, narrowly defined question: the chance of what the CPC calls a historic event, one that would exceed the strength of previous El Niño events dating back to 1950. The agency sets that bar at a 3-month RONI value of +2.5 °C or more. Measured that way, the CPC gave a 54% chance for September–November, 83% for October–December and 70% for November–January.

Those three percentages apply to the RONI threshold in those specific overlapping seasons, and not to any other index or period. The RONI is a different yardstick from the raw Niño-3.4 anomaly quoted earlier in the same discussion, so the two sets of figures are not interchangeable. Background on how the various Niño regions and indices are constructed is available in our science section and glossary.

Impacts framed as probabilities

The CPC was explicit that an event of this size does not lock in outcomes. With an event of this magnitude, the agency wrote, the chances of experiencing impacts consistent with El Niño are larger, though not guaranteed, and it directed readers to its own seasonal outlooks for probabilities of seasonal anomalies rather than to the diagnostic discussion.

The index values reported above are observations the agency logged for the past month; the seasonal percentages are model-based forecasts issued by the CPC, and the agency published them as probabilities rather than as expected outcomes.

Publication schedule

The discussion is described as a consolidated effort of the National Oceanic and Atmospheric Administration, NOAA's National Weather Service and their funded institutions. The CPC notes that oceanic and atmospheric conditions are updated weekly on its website through its El Niño/La Niña current conditions and expert discussions pages, and that a separate probabilistic strength forecast is published online.

The CPC has scheduled the next ENSO Diagnostics Discussion for 12 November 2026, and operates an e-mail notification list for the monthly releases.