The shift in forecasts reflects changes observed across the tropical Pacific Ocean since early 2026. The event was not yet established in March, but warmer sea surface temperatures and atmospheric patterns consistent with El Niño have since emerged, leading scientists to revise their outlooks.
NOAA Forecasts a Very Strong El Niño After Months of Strengthening Signals
El Niño is the warm phase of the El Niño-Southern Oscillation (ENSO), a recurring climate pattern that can influence weather conditions around the world. Its effects vary by region and are not guaranteed in every location, but typical impacts can include wetter conditions in parts of the southern United States and drier conditions in some northern areas.
According to NOAA’s Climate Prediction Center, El Niño strengthened during July, with sea surface temperature anomalies exceeding +2.0°C in the eastern equatorial Pacific. The agency reported that the July Niño-3.4 index reached +1.4°C, while Niño-3 reached +1.7°C and Niño-1+2 reached +2.9°C.
The ocean beneath the surface also showed signs of a strengthening warm event. According to the NOAA Climate Prediction Center’s August 13 ENSO Diagnostic Discussion, subsurface temperature anomalies reached +10.0°C at depth, while a deeper-than-average thermocline and changes in tropical winds supported the development of the event.
Forecast confidence increased steadily through 2026. In March, NOAA estimated only a one-in-three chance of a strong El Niño during October to December. By June, forecasters placed the chance of a very strong event during November to January at 63 percent. The August update raised that probability above 90 percent for the fall and winter period.
A Potential Historic Event Is Being Monitored Through Ocean Measurements
NOAA’s latest outlook indicates that the event could rank among the strongest El Niño episodes recorded since 1950. According to the Climate Prediction Center, there is a 69 percent chance that the October to December 2026 period will produce a Relative Oceanic Niño Index (RONI) value of +2.5°C or higher, which would exceed previous El Niño events in the historical record.
The RONI is used by NOAA to monitor and compare ENSO events over time. The index measures sea surface temperature departures in the Niño-3.4 region while adjusting for tropical average temperatures. NOAA reported that the most recent RONI value for May-July 2026 was 1.0°C.
Current observations show several features linked with the ongoing El Niño. According to NOAA data, above-average sea surface temperatures were present across the east-central and eastern equatorial Pacific, while atmospheric circulation patterns over the region remained consistent with El Niño conditions.
The agency expects El Niño conditions to continue through Northern Hemisphere spring 2027. NOAA will continue updating its assessments as new ocean and atmospheric observations become available, with the next ENSO Diagnostic Discussion scheduled for September 10, 2026.
