The UK is likely to see stormier conditions this autumn due to a powerful natural climate phenomenon developing over the Pacific Ocean. Weather experts say El Niño is set to be the strongest in living memory, resulting in 2027 predicted to become the hottest year on record.
For the rest of 2026, the Met Office has said it is expected to increase the risk of a wet and stormy autumn. This comes after one of the warmest summers on record in Wales, with five heatwaves hitting the region. The unprecedented string of heatwaves and lack of rainfall in recent months brought the driest July in 190 years and pushed almost three-quarters (71.3%) of England and all of Wales into drought, putting severe pressure on the water system, wildlife, farmers, emergency services and infrastructure.
What is El Niño?
The Met Office says the name 'El Niño' is widely used to describe the warming of sea surface temperature that occurs every few years, typically concentrated in the central-east equatorial Pacific. It explains: "An El Niño is declared when sea temperatures in the tropical eastern Pacific rise 0.5 °C above the long-term average. El Niño is felt strongly in the tropical eastern Pacific with warmer than average weather."
The effects of El Niño often peak during December; its name "the boy" is thought to have originated as 'El Niño de Navidad' centuries ago when Peruvian fishermen named the weather phenomenon after the newborn Christ.
What causes it?
The Met Office explains: "The cycle is the consequence of slow feedbacks in the ocean-atmosphere system acting alongside the strong air-sea interaction processes in the tropics that allow the growth of small disturbances to the large-scale ocean state." Normally the equatorial Pacific Ocean has a pool of relatively warm water in the upper ocean in the west and a shallower layer of relatively cool water in the east, maintained by and in balance with easterly surface winds. The well-mixed upper ocean layer (a few tens of metres deep) lies above a thin 'thermocline' layer, with cold water below.
"An El Niño event can start in several ways, usually with the sea surface temperature raised slightly in the central/east Pacific. This may be, for example, through the action of 'westerly windbursts' (short-lived storm-like events in the Western Pacific) that disturb the 'balance' maintained by easterly winds, or through slow evolution of the ocean thermocline as a consequence of a previous event. The increased sea surface temperature influences the atmospheric winds, which in turn influence the upper ocean and the thermocline such that the sea surface temperature is increased further - a positive feedback. When conditions are favourable, this feedback generates an El Niño event."
Wet and stormy autumn and 2027 forecast
Professor Adam Scaife, head of long-range forecasting at the UK Met Office, described it as "an unprecedented event", adding the UK faces greater risk of a wet and stormy autumn. He said: "I have never seen an El Niño signal this intense in our forecasts."
Significant heat is released from the ocean to the atmosphere during El Niño. Dr Nick Dunstone, climate scientist for the Met Office, said: "It can mean an increase in global average temperature, particularly in the calendar year following the winter peak of the El Niño. Hence, 2027 is very likely to replace 2024 as the warmest year on record."
