The unprecedented El Ni帽o gathering strength in the Pacific Ocean could upend forecasts for UK weather this winter, bringing continuously wet, stormy conditions until spring.
El Ni帽o is a natural climate phase that happens when easterly trade winds weaken, allowing the warm water they had piled up in the western Pacific to wash back across the central and eastern Pacific. This swathe of warm water heats the atmosphere and weakens the winds further in a feedback loop.
The phenomenon鈥檚 impact on the weather in the UK and north-western Europe is notoriously tricky to predict, because weather patterns in this region are strongly affected by weather phenomena in the North Atlantic.
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Under an El Ni帽o event of normal intensity, the UK is more likely to experience wetter, windier, stormier weather in the late autumn and early winter, potentially followed by a colder, drier end to winter.
However, the sheer size of the current El Ni帽o 鈥� already one of the largest on record and still intensifying 鈥� could mean that the end of winter and start of spring continue to be wet and stormy, says at the Met Office, the UK鈥檚 national weather service, who leads the agency鈥檚 long-range forecasting.
鈥淲e found that the big events show a slightly different response over the Atlantic,鈥� he says. El Ni帽os usually increase the likelihood of cold easterly winds prevailing over the UK during late winter. But a very strong El Ni帽o may reverse that trend, leading to prevailing westerlies late in the season. The weather under those conditions is 鈥渟till cold, but it鈥檚 not extreme鈥�, he says.
Scaife first reported this effect of strong El Ni帽os in a he co-wrote with , now at NORCE Research in Norway. The study assessed the weather in the North Atlantic during El Ni帽o years and found that very strong El Ni帽os produced this mild and wet pattern in late winter.
The El Ni帽o in 1997-1998, for example, was one of the most powerful on record. It saw high pressure developing in the North Atlantic to the west of the UK over the late winter, leading to westerly prevailing winds that blew milder, wetter, stormier air over the UK and northern Europe. The same pattern appeared in the 2015-2016 El Ni帽o, when the UK had one of its mildest and wettest winters on record.
鈥淲e think that鈥檚 a real effect [of strong El Ni帽os],鈥� says Scaife. 鈥淲e鈥檙e looking for that at the end of this winter.鈥�
A prolonged wet and stormy winter could saturate soils and make parts of the UK more susceptible to severe flooding. But it would also offer an opportunity to replenish reservoirs and groundwater after an exceptionally dry summer.
However, Scaife warns it is very difficult to tease apart the effect of a strong El Ni帽o compared with that of a standard-strength one, in part because there are only a few very strong events in the historical record for which we have good data.
El Ni帽os 鈥� and their opposite pattern, La Ni帽as 鈥� also vary hugely from year to year and decade to decade, so it can be fiendishly difficult to separate out a signal from the noise in the system. What鈥檚 more, it is very difficult to predict weather patterns months in advance, and there is still huge uncertainty over what late winter will hold for the UK.
This week, the World Meteorological Organisation (WMO) warned that the El Ni帽o is still intensifying in the tropical Pacific and is set to be the largest on record, fuelling drought, floods and extreme temperatures around the world. In most cases, a stronger El Ni帽o brings more pronounced impacts globally, such as severe drought in Australia, the Amazon and Indonesia, and heavy rain in parts of South America, East Africa and the southern US.
The pattern is likely to peak in November, but will persist until at least February 2027, the WMO said, bringing extreme impacts that will last well into next year.
