2026 El Niño event

The 2026 El Niño event is an episode of El Niño, the warm phase of the El Niño–Southern Oscillation (ENSO), involving coupled changes in ocean temperatures and atmospheric circulation across the tropical Pacific. The United States Climate Prediction Center (CPC) confirmed its onset on 11 June 2026. As of 14 October 2026, the event was still strengthening, with forecasts indicating strong-to-very-strong conditions into early 2027. Its eventual peak intensity, duration, and complete impacts remained undetermined. (cpc.ncep.noaa.gov)

Development and observed conditions

Onset in mid-2026

The CPC’s June assessment identified above-average sea-surface temperatures across the central and eastern equatorial Pacific, together with atmospheric changes characteristic of El Niño. The latest weekly Niño-3.4 index reported in that assessment was $+0.7\,^\circ\mathrm{C}$, while the easternmost Niño-1+2 index was $+2.1\,^\circ\mathrm{C}$. Warm subsurface waters persisted beneath the central and eastern Pacific. (cpc.ncep.noaa.gov)

The ocean warming was accompanied by anomalous low-level westerly winds, upper-level easterly winds, and negative Southern Oscillation indices. Convection was slightly enhanced over the central and east-central equatorial Pacific and near or below average over Indonesia. These combined observations supported a diagnosis of a coupled ocean–atmosphere event, rather than isolated surface warming. (cpc.ncep.noaa.gov)

Strengthening through October

By the CPC assessment issued on 8 October 2026, sea-surface temperature anomalies exceeded $+4.0\,^\circ\mathrm{C}$ in parts of the eastern equatorial Pacific. The latest reported Niño-region indices were $+2.1\,^\circ\mathrm{C}$ for Niño-3.4, $+3.0\,^\circ\mathrm{C}$ for Niño-3, and $+3.9\,^\circ\mathrm{C}$ for Niño-1+2. These indices describe different monitoring regions and should not be treated as interchangeable measures of event strength. (cpc.ncep.noaa.gov)

The October assessment also reported a deeper-than-average thermocline and subsurface temperature anomalies exceeding $+10.0\,^\circ\mathrm{C}$ at depth in the eastern Pacific. Rainfall and convection were enhanced from the central to eastern Pacific and suppressed over Indonesia, while both traditional and equatorial Southern Oscillation indices were significantly negative. (cpc.ncep.noaa.gov)

Physical basis

El Niño involves interaction between the ocean and the atmosphere, not simply an increase in water temperature. Under ordinary tropical Pacific conditions, the Walker circulation reflects the contrast between the warmer western Pacific and cooler eastern Pacific. During El Niño, this circulation weakens or changes, and warm water extends farther east toward South America. The 2026 event exhibited both ocean warming and the associated atmospheric response. (noaa.gov)

The substantial reservoir of subsurface warmth was important to forecasts of further development. In June, the CPC linked its confidence in continued strengthening to unusually high oceanic heat content and expanding westerly wind anomalies across the equatorial Pacific. (cpc.ncep.noaa.gov)

Measurement and classification

Relative Oceanic Niño Index

The event developed during a change in NOAA’s operational ENSO monitoring. Effective 1 February 2026, the CPC adopted the Relative Oceanic Niño Index (RONI) for official monitoring and prediction. Unlike the traditional Oceanic Niño Index, RONI compares warming in the Niño-3.4 region with warming across the wider tropical oceans, reducing sensitivity to the choice of climatological reference period. (weather.gov)

RONI is a three-month running average based on Niño-3.4 sea-surface temperature anomalies, with the tropical mean anomaly subtracted and the resulting difference rescaled to preserve the original index’s variance. Consequently, weekly regional temperature anomalies, conventional seasonal indices, and seasonal RONI values are related but distinct quantities. NOAA also cautions that the most recently published RONI estimates can be revised as the underlying sea-surface temperature analysis is updated. (cpc.ncep.noaa.gov)

“Very strong” and “super El Niño”

“Very strong” is used in operational assessments of ENSO intensity. The expression “super El Niño”, although used outside those assessments, is not part of the World Meteorological Organization’s standardized operational classification. Describing the 2026 episode as “super” therefore does not establish a separate scientific category or a completed historical ranking. (wmo.int)

Forecast intensity and duration

The October CPC forecast assigned an 83% probability to a three-month RONI value of at least $+2.5\,^\circ\mathrm{C}$ during October–December 2026. The assessment described that outcome as potentially exceeding the strength of earlier El Niño events in the record beginning in 1950. This was a forecast probability, not confirmation that a record seasonal peak had already occurred. (cpc.ncep.noaa.gov)

The accompanying official outlook gave median RONI forecasts of $+2.74\,^\circ\mathrm{C}$ for October–December 2026, $+2.65\,^\circ\mathrm{C}$ for November 2026–January 2027, and $+1.90\,^\circ\mathrm{C}$ for January–March 2027. Its central forecast then indicated weakening during spring 2027. These values represented a distribution of possible outcomes derived from multiple climate models and observations, rather than a fixed future trajectory. (cpc.ncep.noaa.gov)

Climate effects and attribution limits

The World Meteorological Organization’s September assessment indicated increased chances of above-normal temperatures across almost all land areas for September–November 2026, together with rainfall patterns characteristic of a strong Pacific El Niño. It also identified the expected positive Indian Ocean Dipole and warm tropical Atlantic conditions as factors capable of modifying regional outcomes. Event strength alone does not determine the severity of impacts in an individual country. (public.wmo.int)

For the United States, NOAA described the usual El Niño winter tendencies as a southward-shifted Pacific jet stream and storm track, wetter or stormier conditions across the southern tier, and warmer conditions across the north. El Niño also generally favors reduced Atlantic tropical cyclone development and enhanced development in the eastern and central Pacific. These are climatological tendencies, not a catalogue of impacts already observed during the 2026 event. (noaa.gov)

A stronger event can increase confidence in some expected regional responses without guaranteeing them. Conditions in other ocean basins, the season, and regional atmospheric variability can reinforce or counteract ENSO influences. Comparisons with earlier events also require consistent indices and averaging periods; an extreme local temperature anomaly cannot by itself establish the event’s overall historical rank. (cpc.ncep.noaa.gov)

References

1. Climate Prediction Center: ENSO Diagnostic Discussion, 11 June 2026cpc.ncep.noaa.gov
2. Climate Prediction Center: ENSO Diagnostic Discussion, 8 October 2026cpc.ncep.noaa.gov
3. El Nino forms, expected to strengthen, say NOAA forecastersnoaa.gov
4. Public Information Statement 26-05: Relative Oceanic Niño Indexweather.gov
5. CPC adopts Relative Oceanic Niño Index (RONI) for reliable, responsive monitoring and tracking of ENSOcpc.ncep.noaa.gov
6. Climate Prediction Center: Relative Oceanic Niño Index (RONI)cpc.ncep.noaa.gov
7. WMO: Prepare for El Niñowmo.int
8. Official NOAA Relative Oceanic Niño Index (RONI) Outlookcpc.ncep.noaa.gov
9. El Niño set to become very strong, raising risks of extreme weather into 2027public.wmo.int