Record Pacific Heat Signals a Powerful El Niño, Raising Global Weather Risks in 2027

The Niño 3.4 index, which tracks sea-surface temperature departures from normal in the central-eastern equatorial Pacific, rose from +1.6°C in June 2026 to +2.5°C in August.

Sea temperatures in the central and eastern tropical Pacific are forecast to reach record levels during October–December 2026, feeding a strengthening El Niño that could reshape weather far beyond the ocean where it began. The World Meteorological Organization's monthly Global Seasonal Climate Update points to a December peak, with rising risks of extreme heat, drought and floods affecting communities, economies and ecosystems across the globe. For people whose livelihoods depend on reliable rainfall or manageable temperatures, the forecast brings growing concern about the months ahead.

A warmer ocean feeds an exceptional event

WMO Secretary-General Celeste Saulo says El Niño is firmly established and strengthening rapidly, with a nearly 100% chance of continuing through February 2027 and the potential to become one of the strongest events since at least 1950. That confidence comes from agreement across thirteen national and international forecasting centres, stretching from Washington and Tokyo to London and Pune, supported by ocean buoy, satellite and radiosonde observations shared in real time through WMO's coordinated network.

The Niño 3.4 index, which tracks sea-surface temperature departures from normal in the central-eastern equatorial Pacific, rose from +1.6°C in June 2026 to +2.5°C in August. Its October–December seasonal average is forecast to reach approximately +3.7°C, exceeding the previous record of +2.6°C during November 2015–January 2016. Forecasts starting from September observations show further strengthening towards December, with anomalies measured against the 1993–2009 baseline. These numbers describe how much warmer the water is than average, rather than its actual temperature.

Speaking at the Global Heat Forum in Bangkok, Saulo explained that El Niño releases heat already stored beneath the ocean's surface, helping push global temperatures higher rather than creating new heat. She pointed to 2024 as an example of the intense warmth associated with a strong event and stressed that the ocean now holds an unprecedented amount of heat available for release. Reports from the EU's Copernicus Climate Service, NOAA and NASA identified August as the hottest recorded, with global sea-surface temperatures also reaching an observed all-time high.

Heat spreads, rainfall patterns change

The October–December outlook shows an overwhelming likelihood of temperatures above the 1993–2009 average across large areas of the world, increasing the chances of heat extremes and related impacts. A warmer seasonal average does not mean every place will experience unusual warmth every day, and the rainfall forecasts describe probabilities rather than guaranteed outcomes. Families, farmers and local authorities still need national and local forecasts to understand what these broad signals could mean for their own communities.

Above-normal rainfall is most strongly favoured across the central and eastern equatorial Pacific east of the Date Line, with wetter conditions also more likely in the Greater Horn of Africa, parts of Central Asia and coastal East Asia, northern areas of the Arabian Peninsula, parts of North America south of 45°N, and southeastern South America. The dry outlook covers the western Pacific and equatorial Atlantic, extending across the South Pacific towards South America's southern tip; reduced rainfall is also forecast for the Indian subcontinent, southern Central America, parts of the Caribbean and northwestern South America.

Conditions in other oceans help shape this picture: a positive Indian Ocean Dipole, which influences rainfall around the Indian Ocean, is expected to peak in October before declining, with an October–December seasonal anomaly of about +0.5°C. Equatorial Atlantic sea-surface temperatures are forecast to remain above normal. The monthly update brings these influences together with the El Niño–Southern Oscillation, complementing WMO's quarterly El Niño/La Niña Update to give decision-makers a fuller view of seasonal risks.

Turning the forecast into preparation

WMO and its members are mobilising across economic sectors, with national meteorological and hydrological services and regional climate outlook forums regularly briefing decision-makers. Updates shared through the WMO Coordination Mechanism are helping UN agencies and humanitarian partners prepare for changing risks. The strengthening El Niño and associated extreme heat are also central themes at the Global Heat Forum in Bangkok, running from October 6–9, with WMO among its sponsors, where 600 experts are meeting to turn climate science into practical, sustainable responses that help protect lives and livelihoods.