Forecast El Niño Peak Beats the 2015 Record by 1.1C

The World Meteorological Organization expects sea-surface temperatures in the heart of the tropical Pacific to average about 3.7C above normal between October and December 2026. The previous record for that measure, the Niño 3.4 index, was 2.6C, set across November 2015 to January 2016. WMO published the forecast in its monthly Global Seasonal Climate Update on 8 October 2026 and expects the event to peak around December.

The index has moved fast. It averaged 1.6C above normal in June 2026 and 2.5C in August, and the forecast now adds more than another degree on top of a figure that was already at the edge of the observational record.

Thirteen centres, one number

That near-certainty is not one model's output. WMO says it reflects a consensus across thirteen national and international forecasting centres, from Washington to Tokyo to London to Pune, built on real-time exchange of ocean buoy, satellite and radiosonde data that the organisation coordinates. Two other basins feed the seasonal outlook: a positive Indian Ocean Dipole, forecast at about +0.5C for October to December and expected to peak in October before declining, and equatorial Atlantic sea-surface temperatures that are expected to stay above normal.

September already set a record

The ocean is arriving at this point unusually warm. NOAA's National Centers for Environmental Information reported on 9 October that global sea surface temperature departures from average in September 2026 reached an all-time high for any month, beating the record set in August 2026. The same report put September as the second-warmest September in the 1850 to 2026 record, 1.33C above the 20th-century average and 0.07C behind September 2023, with the Arctic, North America and Asia each recording their warmest September. NOAA attributes record warmth across the central and eastern tropical Pacific to the El Niño conditions themselves.

The last event of this kind is the reason the forecast matters beyond the index. A study in Earth's Future, which Parallax Nexus covered on 8 October, found that 75 per cent of tropical forests endured simultaneous extreme heat and drought for an average of six months during the 2023-24 El Niño. That event peaked at an anomaly well below the one now forecast.

Released heat, not new heat

Saulo was careful at the Global Heat Forum in Bangkok about what the event does and does not do. "El Niño doesn't add new heat to the planet. It releases heat the ocean has already been storing beneath the surface," she said, adding that "the ocean it's drawing from is the warmest we've ever measured it. There is simply more heat available to release." The honest reading is that the 3.7C figure is a redistribution number rather than a forcing number, and it is large mainly because the reservoir behind it is.

What is not known is how much of the forecast survives contact with December. WMO's figure is an ensemble mean across thirteen systems initialised in September, and seasonal forecasts of El Niño amplitude three months ahead carry real spread; the organisation publishes the model lines precisely because they disagree. The comparison with 2015-16 is like-for-like on WMO's own 1993-2009 baseline, but anomalies quoted elsewhere against a 1991-2020 baseline will read lower, which is a frequent source of confusion when these numbers circulate.