CPC Keeps El Niño Advisory as Niño 1+2 Runs 3.2 °C Above Average

NOAA's Climate Prediction Center held its ENSO Alert System at an El Niño Advisory in the ENSO evolution and forecast update prepared on 24 August 2026, reporting that El Niño is present and strengthening, 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.

A basin divided at the Date Line

The weekly sea surface temperature departures listed by the CPC describe a sharply tilted Pacific: +3.2 °C in the Niño 1+2 region nearest South America, +2.5 °C in Niño 3, +1.8 °C in Niño 3.4 and 0.0 °C in Niño 4. Over the four weeks covered by the deck, the agency says, equatorial temperatures were above average east of the Date Line and below average to the west, with positive anomaly changes across the east-central Pacific and negative changes across the west-central Pacific and near Indonesia.

The CPC's narrative of 2026 runs as follows. Through February, below-average temperatures covered most of the equatorial Pacific. Above-average water emerged in the far eastern equatorial Pacific in early February and then generally expanded across the east-central and eastern Pacific from mid-April. Since mid-June, the agency adds, below-average equatorial temperatures have expanded to the Date Line.

Below the surface, the CPC reports upper-ocean (0–300 m) heat content anomalies above average and a thermocline slope index below average, the combination it associates with a warm episode. Positive subsurface anomalies developed and grew from mid-December 2025 through late April 2026, decreased from late April to late May, increased again from late May to late July, and have since remained steady. Downwelling oceanic Kelvin waves were initiated in December 2025 and in January, March and June 2026, after upwelling waves in August and October 2025.

In the atmosphere, the CPC describes below-average outgoing longwave radiation — enhanced convection and rainfall — 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 westerly wind anomalies at 850 hPa ran from the western to the east-central equatorial Pacific, with easterly anomalies over the eastern Pacific.

Reading the indices as the deck presents them

Two different measures appear in the update and are not interchangeable. The Niño-region figures above are weekly departures drawn from the OISSTv2.1 dataset used for the CPC's weekly monitoring slides. The Relative Oceanic Niño Index, or RONI, is a separate three-month running-mean quantity: the Niño 3.4 (5°N–5°S, 120°–170°W) departure with the tropical mean (20°S–20°N) departure subtracted and the variance rescaled, computed from the ERSST reconstruction. The most recent RONI value in the deck, for May–July 2026, is 1.0 °C, after 0.5 °C in April–June and 0.0 °C in March–May. The CPC calls RONI one measure of the El Niño–Southern Oscillation, useful for placing events in historical perspective, and notes that other indices can confirm whether coupled ocean-atmosphere features accompanied a given period. No Oceanic Niño Index value is given in this update. The operational definitions printed in the deck are stated in RONI terms: at or beyond ±0.5 °C, with full episode classification requiring at least five consecutive overlapping three-month seasons past the threshold. The CPC also flags a dataset change — from 10 August 2026, with NCEI discontinuing ERSSTv5, RONI values switched to ERSST.v6, while weekly OISSTv2.1 monitoring is unaffected.

The outlook, stated in probabilities

The CPC's probabilistic outlooks, updated 13 August 2026, assign a greater than 90% chance to a very strong El Niño for the seasons from September–November through November–January 2026-27; the update does not specify the numeric anomaly bounds that define that strength category. El Niño is expected to persist through Northern Hemisphere spring 2027, in the agency's wording. Separately, the NCEP CFS.v2 forecast issued with the 24 August deck — model output rather than observation, and one modelling system rather than a multi-agency comparison — has an ensemble mean that the CPC says favors El Niño continuing through Northern Hemisphere winter 2026-27.

For North America, the CPC reports that height anomalies over the North Pacific and the contiguous United States have been variable since late June, with above-average heights and temperatures over the west-central contiguous United States since late July. Its September–November 2026 seasonal outlooks combine long-term trends, soil moisture and, where appropriate, ENSO. The summary statements are refreshed monthly, on the second Thursday, alongside the ENSO Diagnostics Discussion.