Japan and China confirm the event
Japan's Meteorological Agency said on Friday, 9 October, that El Niño had strengthened to its strongest level on record since September, and gave a 100% chance that the conditions will continue into the Northern Hemisphere winter. The sea surface temperature anomaly in the El Niño monitoring region reached +4.0°C in September, the highest since records began in 1949. The agency put the previous record at +3.6°C, set in December 1997. China's National Climate Centre said separately that the super El Niño officially formed in September, after rapid warming of the Pacific Ocean from May to September met the criteria for the extreme climate event. Both announcements came on the same day, 9 October.
WMO outlook through the winter
The World Meteorological Organization (WMO) expects El Niño to keep strengthening before peaking in December, with a probability close to 100% that it persists until February 2027. Its forecast for October to December puts the seasonal sea surface temperature anomaly at about +3.7°C, above the previous WMO record of +2.6°C recorded between November 2015 and January 2016. The Niño 3.4 index, which tracks the central and eastern equatorial Pacific, rose from an average of +1.6°C above normal in June 2026, the month the US Weather Service announced the phenomenon's return, to +2.5°C in August. The WMO said its outlook is a consensus of 13 national and international centres, from Washington to Tokyo, London and Pune, which exchange real-time data from ocean buoys, satellites and radiosondes. WMO Secretary-General Celeste Saulo said the event could be one of the most intense since at least 1950. Saulo explained the mechanism two days earlier at the World Heat Forum in Bangkok.
Heat, rainfall and health risks
The WMO expects temperatures above average across much of the planet in the coming months, along with changes to rainfall patterns that raise the risk of droughts and floods in several regions. In Bangkok, Saulo explained where the extra heat comes from:
El Niño does not add more heat to the planet, but releases heat that the ocean has already stored below the surface.
Saulo added that the ocean supplying this heat is the warmest ever measured, which is why a strong event often coincides with one of the hottest years on record, as happened in 2024. The phenomenon is already upending weather across South America and Asia, with economic disruptions that could linger long after the pattern dissipates. In September, researchers at the University of Chicago's Climate Impact Lab predicted that this super El Niño could cause up to 451,000 deaths worldwide between June 2026 and February 2027.
What happens next
El Niño recurs every two to seven years and typically lasts nine to twelve months, so the current episode is set to run past the winter. The next milestone in the forecast is the December peak, when the WMO expects sea surface temperatures in the central and eastern tropical Pacific to reach record levels in October, November and December.
- Rapid Pacific warming begins, continuing through September
- US Weather Service announces the return of the phenomenon
- Niño 3.4 index reaches +2.5°C above normal, up from +1.6°C in June
- Japan records a +4.0°C anomaly, and China's centre says the event formed
- WMO expects the peak, with an anomaly of about +3.7°C for October to December
- WMO gives a near 100% probability that conditions persist
After the peak, the WMO gives a probability close to 100% that conditions persist until February 2027, and the Japanese agency expects them to continue into the Northern Hemisphere winter. The 451,000 death estimate covers a period that is still under way, so it remains a projection rather than a count.