CPC: Over 90% Odds of a Very Strong El Niño, 69% Chance of a Record Event

NOAA's Climate Prediction Center says El Niño is present and strengthening in the tropical Pacific, and now puts the odds of a very strong event during the Northern Hemisphere fall and winter of 2026-27 at greater than 90 percent. The assessment comes in the centre's ENSO evolution, status and predictions update dated 17 August 2026, which keeps the ENSO Alert System status at El Niño Advisory.

The most striking number in the deck concerns the upper end of the strength distribution. For the October–December 2026 season, the CPC's Official ENSO Outlook, updated 13 August 2026, assigns a 69 percent chance of what the centre calls a historic event — one that would exceed the strength of previous El Niño episodes dating back to 1950. The centre also expects El Niño to persist through Northern Hemisphere spring 2027.

An ocean that flipped in six months

The CPC's account of the year so far describes a rapid reversal. Through February 2026, below-average sea surface temperatures covered most of the equatorial Pacific. Above-average SSTs appeared in the far eastern equatorial Pacific in early February, and since mid-April warmth has expanded across the east-central and eastern basin.

The latest weekly SST departures listed by the CPC show a strong east–west gradient: +3.2ºC in Niño 1+2, +2.5ºC in Niño 3, +1.8ºC in Niño 3.4, and +0.2ºC in Niño 4. Over the past four weeks, the centre reports, equatorial SSTs were above average east of the Date Line and below average to the west, with the positive anomalies amplified east of the International Date Line.

Beneath the surface, the CPC says upper-ocean heat content anomalies are above average and the thermocline slope index is below average — both patterns the centre associates with warm episodes. Positive subsurface anomalies developed from mid-December 2025 through late April 2026, eased between late April and late May, and increased again from late May onward. Downwelling equatorial Kelvin waves were initiated in December 2025, January 2026, March 2026 and June 2026, according to the deck, with positive subsurface anomalies now persisting east of the Date Line.

The atmosphere is responding in step. The CPC reports enhanced convection along the equator from near the Date Line eastward, suppressed convection over the Philippines, Indonesia and Papua New Guinea, and low-level westerly wind anomalies from the western to the east-central equatorial Pacific over the last 30 days. Easterly anomalies have generally prevailed over the far eastern Pacific. The centre judges these circulation anomalies to be consistent with El Niño.

Index bookkeeping: a switch to ERSSTv6

The update also flags a data change. As of 10 August 2026, NOAA's National Centers for Environmental Information is discontinuing ERSSTv5, and the CPC's Relative Oceanic Niño Index values have switched to ERSSTv6; weekly SST monitoring continues to use OISSTv2.1. Both index tables remain available from the centre.

The RONI is described by the CPC as a measure that subtracts tropical-mean (20ºS–20ºN) SST departures from the Niño 3.4 anomaly to place events in historical perspective. The deck states NOAA's operational thresholds in terms of that index: El Niño at +0.5ºC or above, La Niña at −0.5ºC or below, with a full episode requiring at least five consecutive overlapping three-month seasons beyond the threshold. Conditions are considered present when monthly relative Niño 3.4 departures meet the threshold alongside consistent atmospheric features and are forecast to persist for three months. The most recent RONI value, for May–July 2026, is 1.0ºC, having climbed from 0.0ºC in March–May and 0.5ºC in April–June, per the CPC's table.

What the models show

The NCEP CFS.v2 forecast issued 17 August 2026 — model output rather than observation — has an ensemble mean that favours El Niño continuing through Northern Hemisphere winter 2026-27. For the United States, the CPC notes only that its August–October 2026 seasonal temperature and precipitation outlooks combine long-term trends, soil moisture and, where appropriate, ENSO; over the past 60 days it observed above-average heights and temperatures across the west-central contiguous states since mid-July. Related background is available on our science and glossary pages.

The CPC updates these statements once a month, on the second Thursday, alongside its ENSO Diagnostics Discussion.