A Record El Niño Is Building Toward a December Peak
Temperatures above 30C have been recorded for the first time in parts of the tropical Pacific, as record sea-surface temperature anomalies and exceptional subsurface warmth meet in the equatorial Pacific zone used to monitor El Niño. BBC
An anomaly means a departure from the long-term average. Forecasts from the European Centre for Medium Range Weather Forecasts and the US National Oceanic and Atmospheric Administration indicate El Niño is likely to peak in December. The warmth now stretches well beyond the tropical region normally used to monitor El Niño. Comparisons with the major events of 1972-73, 1982-83, 1997-98 and 2015-16 show much more widespread ocean warmth across the Pacific and into the Gulf of Mexico.
Berkeley Earth climate scientist Dr Zeke Hausfather said: "We are currently witnessing an El Niño event that is unprecedented in the historical record."
Heat from surface to depth
NOAA's Climate Prediction Center reported sea surface temperature anomalies exceeding +4.0°C in portions of the eastern equatorial Pacific in its 8 October discussion. NOAA Climate Prediction Center The peak is still ahead. The same assessment put the Niño-3.4 index at +2.1°C, the Niño-3 index at +3.0°C, and the Niño-1+2 index at +3.9°C. These indices track different slices of the equatorial Pacific.
Below the surface, the pattern is also extreme. Subsurface temperatures in excess of +10.0°C at depth were reported in the eastern Pacific Ocean. The equatorial subsurface temperature index averaged from 180°-100°W was well above average, reflecting a deeper-than-average thermocline, the boundary between warm surface water and colder deep water.
The atmosphere is coupled to the ocean. Low-level westerly wind anomalies and upper-level easterly wind anomalies stretched from the western to the east-central equatorial Pacific. Enhanced convection and rainfall, meaning rising air and cloud formation, persisted from the central to the eastern Pacific, while anomalies remained suppressed over Indonesia. The traditional and equatorial Southern Oscillation indices, which measure pressure differences, were significantly negative.
The World Meteorological Organization forecast that the October-November-December seasonal average Niño 3.4 sea surface temperature anomaly will reach approximately +3.7°C, peaking around December. WMO
NOAA's Climate Prediction Center forecast El Niño will continue to strengthen through the end of the year, with a strong-to-very strong El Niño likely through January-March 2027 at greater than 83% chance. The next ENSO Diagnostics Discussion is scheduled for 12 November 2026.
A new yardstick and a December peak
Australian and US official forecasters are now using a Relative Ocean El Niño Index (RONI) to remove the additional human-induced warming signal and enable better comparison to historical events. NOAA's Climate Prediction Center defined a historic El Niño exceeding previous events dating back to 1950 as +2.5°C or more for a 3-month RONI value.
On that basis, the Center estimated a 54% chance of a historic El Niño for September-November, 83% for October-December, and 70% for November-January. NOAA CPC also issued ENSO Strength Probabilities in October 2026, showing the chance of El Niño as red bars and ENSO-Neutral as grey bars for nine upcoming overlapping periods.
The Australian Bureau of Meteorology's average weekly RONI data only goes back to 2008. On the RONI measure, the Bureau's average weekly data now exceeds levels during the record-breaking December of 2015.
Earlier assessments pointed in the same direction. The BBC reported on 22 September that the developing El Niño is now the strongest on record, with weather impacts already being felt around the world. Carbon Brief published an analysis stating the 2026 El Niño is on track to smash the all-time record, and Down To Earth reported on 9 October that El Niño is still strengthening and could reach unprecedented levels. The UK Met Office published a blog titled "Record-Breaking El Niño Surpasses Previous Benchmarks" on 22 September, after earlier blogs in June and August that El Niño conditions had developed and that 2026 would be renowned for the development of the largest El Niño in living memory.
WMO stated in August that El Niño is firmly established and is expected to strengthen further, later saying it will intensify into a very strong event in the coming months. NOAA forecasters had predicted in June that El Niño would intensify to a moderate or strong level in the fall. The UK Met Office reported that 2025 was the warmest year on record where El Niño conditions did not occur during at least part of the year.
The World Meteorological Organization says there is currently no evidence that climate change is making El Niño events stronger or more frequent.
The broader context here is measurement as much as magnitude. Absolute temperatures were always likely to break records in a warming ocean, which is why Canberra and Washington shifted to RONI. That the event still exceeds December 2015 on that adjusted scale, and that NOAA assigns an 83% probability to a historic October-December value above any three-month RONI since 1950, separates background warming from ENSO dynamics.
In my view, the geography matters as much as the indices. Past super-events concentrated anomalies in the eastern equatorial cold tongue. Current warmth stretching across the basin and into the Gulf of Mexico alters teleconnection pathways, the distant links through which El Niño affects regional weather, and lead times for regional impacts. Forecasters will be watching whether coupling persists through the boreal winter peak and into January-March 2027, when global impacts typically lag the oceanic maximum. What remains is calibration of impacts, not direction of travel.
