CPC's 19 October Deck: Niño 1+2 at 4.4 °C, RONI Reaches 1.7 °C

The NOAA Climate Prediction Center kept its ENSO Alert System at El Niño Advisory in the slide deck it issued on 19 October 2026, reporting that the event is still strengthening and that equatorial sea surface temperatures remain above average across the east-central and eastern Pacific.

In the agency's summary, El Niño is present, atmospheric circulation anomalies over the equatorial Pacific are consistent with the event, and a strong-to-very-strong El Niño is considered likely through January-March 2027, with that probability remaining greater than 83%.

Where the indices stand

The CPC deck lists the latest weekly sea surface temperature departures by Niño region: Niño 4 at -0.1 ºC, Niño 3.4 at 2.4 ºC, Niño 3 at 3.5 ºC and Niño 1+2 at 4.4 ºC. The east-west split that those numbers imply is described directly by the agency: over the last four weeks, equatorial sea surface temperatures were above average east of the Date Line and below average near and west of it.

CPC also reports that above-average sea surface temperatures were prevalent over most of the global oceans during the same four-week window, with near-to-below-average values around Indonesia, above-average values in the equatorial Indian Ocean, and amplified warmth east of the Date Line in the Pacific.

On the Relative Oceanic Niño Index — which the deck describes as "a principal measure for monitoring, assessing, and predicting ENSO" and which subtracts the 20ºS-20ºN tropical mean from Niño 3.4 departures — the most recent value, for July-September 2026, is 1.7 ºC. CPC's table of three-month RONI seasons shows the 2026 sequence climbing from -0.9 ºC in December-February to 0.0 ºC in March-May, 0.5 ºC in April-June, 1.0 ºC in May-July, 1.4 ºC in June-August and 1.7 ºC in July-September. The agency's operational definition, as stated in the deck, requires a RONI of +0.5 ºC or more sustained across at least five consecutive overlapping three-month seasons for a full-fledged El Niño episode.

Below the surface and in the atmosphere

CPC reports that upper-ocean (0-300 m) heat anomalies are above average and the thermocline slope index is below average, both consistent with a warm episode. Positive subsurface temperature anomalies increased from late May to late July 2026 and have since remained steady, the agency says, and above-average subsurface temperatures have persisted across the east-central and eastern Pacific over the last two months. Downwelling Kelvin waves were initiated in December 2025, January 2026, March 2026 and June 2026, according to the deck.

In the atmosphere, CPC notes below-average outgoing longwave radiation — indicating enhanced convection and rainfall — along the equator from near the Date Line to the eastern Pacific over the last 30 days, with suppressed convection over the Philippines, Indonesia and Papua New Guinea. Low-level westerly wind anomalies at 850 hPa extended from the western to the east-central equatorial Pacific.

The forecast and a data change

CPC's probabilistic outlook, updated 8 October 2026, has El Niño expected to persist through March-May 2027, with chances favouring ENSO-neutral in April-June and May-July 2027. The same update puts the odds of a historic event — defined by the agency as a three-month RONI of +2.5 ºC or more, exceeding every El Niño back to 1950 — at 54% for September-November, 83% for October-December and 70% for November-January. The NCEP CFS.v2 ensemble mean, model output issued 19 October 2026, favours El Niño continuing through Northern Hemisphere winter 2026-27.

The deck also flags a dataset change: as of 10 August 2026, with NCEI discontinuing ERSSTv5, RONI values have switched to ERSST.v6, while the weekly OISSTv2.1 data used for the Niño-region monitoring slides is unaffected. CPC says both tables remain available. The full update is published on the CPC website, and the summary statements are refreshed monthly alongside the ENSO Diagnostics Discussion.