The Met Office has warned that this year's El Niño could be the "largest in living memory" and an "unprecedented event", increasing the chances of wetter, stormier conditions for northwest Europe, including the UK, in the coming autumn and early winter. Atmospheric waves triggered by El Niño destabilise the polar vortex, also increasing the chance of heavy snow, experts added.
Unprecedented El Niño signal
Professor Adam Scaife, head of Long Range Forecasting at the Met Office, said: "I have never seen an El Niño signal this intense in our forecasts. A typical El Niño leads to an equatorial Pacific sea-surface temperature rise of between 1 and 2 degrees, with 2°C being a really big event."
He added: "This implies that if the forecast is accurate - and other forecast systems show similar extreme values - then 2026 will far exceed our recent experience of El Niño and its worldwide climate influences. We should be clear that this is an unprecedented event."
Wetter and stormier odds
There is twice the normal chance of the October to December period being wet overall, while windy and mild weather is also more likely than usual. El Niño is a naturally occurring climate phenomenon that develops in the Pacific Ocean when sea surface temperatures across the central and eastern equatorial Pacific become significantly warmer than average, changing atmospheric circulation patterns and affecting weather worldwide.
Dr Will Lang, chief forecaster at the Met Office, described it as a "subtle shift in the odds" rather than a definite prediction of wetter, milder and windier conditions. He said, however, that "we are going in with a heightened potential for wet weather, heightened potential for potentially stormy conditions, and that leads through to a heightened potential for flooding".
Polar vortex and cold weather risk
A Met Office spokesperson added: "Through the latter part of the winter, following a peak in El Niño, the stratospheric Polar Vortex can become weaker, leading to an increased chance of Sudden Stratospheric Warming (SSW) events unfurling, increasing the potential for cold weather."
SSW relates to warming between 10km and 50km above the Earth's surface. This phenomenon can cause cold air to rush downwards, impacting the jet stream and potentially creating a "blocking pattern", which could cause cold conditions to stay for the remainder of the year.
