Late-October ENSO Deck: CPC Logs Niño 3 at 3.6 °C, Niño 4 at Zero

The NOAA Climate Prediction Center kept its ENSO Alert System at El Niño Advisory in the monitoring deck it published on 26 October 2026, reporting that El Niño is present, that equatorial sea surface temperatures are above average across the east-central and eastern Pacific, and that atmospheric circulation anomalies over the equatorial Pacific are consistent with El Niño. The agency said the event continues to strengthen.

Where the Niño regions stand

The CPC listed the latest weekly sea surface temperature departures region by region: 4.4 °C in Niño 1+2, 3.6 °C in Niño 3, 2.5 °C in Niño 3.4 and 0.0 °C in Niño 4. That east-heavy gradient matches the four-week picture the agency describes, in which equatorial SSTs ran above average east of the Date Line and below average near and west of it. Globally over the same four weeks, the CPC reported above-average SSTs across most of the world's oceans, with equatorial values near to below average around Indonesia and above average in the Indian Ocean and the western and eastern Atlantic.

The deck also tracks the Relative Oceanic Niño Index, a supplementary diagnostic that takes the Niño 3.4 anomaly and subtracts the tropical mean (20°S–20°N) SST departure, with the variance rescaled and a three-month running mean applied. The CPC gives the most recent RONI value, for July–September 2026, as 1.7 °C, following a rise through the year from -0.4 °C in February–April, 0.0 °C in March–May, 0.5 °C in April–June, 1.0 °C in May–July and 1.4 °C in June–August. The agency notes that RONI values switched to the ERSSTv6 dataset on 10 August 2026 after NCEI discontinued ERSSTv5, while the weekly OISSTv2.1 data used for region monitoring is unaffected. For historical classification, the deck states that a threshold of ±0.5 °C must be met for at least five consecutive overlapping three-month seasons before a period is counted as a full episode.

Below the surface and in the atmosphere

The CPC reported that recent upper-ocean (0–300 m) heat anomalies are above average and the thermocline slope index is below average — the configuration the agency associates with a Pacific warm episode. Positive subsurface anomalies increased from late May to late July 2026 and have since held steady, with above-average subsurface temperatures persisting across the east-central and eastern Pacific over the past two months.

Over the last 30 days, the agency observed below-average outgoing longwave radiation, indicating enhanced convection, along the equator from near the Date Line to the eastern Pacific, and above-average OLR, indicating suppressed convection, over the Philippines, Indonesia and Papua New Guinea. Low-level 850-hPa westerly wind anomalies extended from the western to the east-central equatorial Pacific. The deck records downwelling oceanic Kelvin waves initiated in December 2025, January 2026, March 2026 and June 2026, and upwelling waves initiated in October 2025, with positive subsurface anomalies currently east of the Date Line and strengthened negative anomalies to the west.

The outlooks

The probabilistic outlooks reproduced in the deck carry an update date of 8 October 2026. The CPC expects El Niño to persist through March–May 2027, with chances favouring ENSO-neutral in April–June and May–July 2027. Its strength outlook makes a strong-to-very strong El Niño the most likely category through January–March 2027.

Separately, the agency said chances remain high for a historic event that would exceed the strength of previous El Niño episodes back to 1950, which it defines as a three-month RONI value of +2.5 °C or more. The CPC put that probability at 54% for September–November, 83% for October–December and 70% for November–January.

The NCEP CFS.v2 forecast issued 26 October 2026 — model output rather than observation — has its ensemble mean favouring El Niño continuing through Northern Hemisphere winter 2026-27. The CPC's November 2026–January 2027 seasonal outlooks for U.S. temperature and precipitation combine long-term trends, soil moisture and, where appropriate, ENSO. The full slide deck is published by the CPC.