UK Records Hottest May Day in 79 Years as Iberian Plume Pushes London Toward Historic Bank Holiday Heat

Britain just lived through its hottest May day in at least 79 years, with the Met Office confirming temperatures hit 32.3 degrees Celsius — about 90 degrees Fahrenheit — at Kew Gardens in southwest London on Sunday, the highest May reading anywhere in the U.K. since 1947. Forecasters say the bank holiday Monday is likely to surpass even that mark, with London and the South East expected to push toward 34C and the national May record of 32.8C, set at Camden Square in May 1944, now in serious danger of falling.

Met Office chief meteorologist Tony Wisson said the heat was being driven by an unusually intense "Iberian plume," a warm air mass pushed north from Spain and the Sahara by a stalled jet stream and reinforced by sea-surface temperatures off the English coast running 2 to 3 degrees above the long-term average. "What is remarkable is not just the peak temperature but the persistence," Wisson told the BBC. "We are seeing tropical nights, where minima do not fall below 20C, across much of southeast England — something that used to be a once-a-decade event in May and is now happening multiple times each spring."

Wales recorded its hottest May day on record Sunday with 27.4C at Cardiff's Bute Park, and Northern Ireland matched its 2026 high of 23.4C at Armagh. Scotland remained noticeably cooler under a band of cloud, but East Lothian still touched 25C, the warmest May reading there since 2017. The U.K. Health Security Agency extended an amber heat-health alert across nine English regions through Tuesday, warning of "significant impacts likely across the whole health and social-care sector" and urging households to check on elderly relatives.

The surge in temperature collided with the long weekend's outdoor traditions. Brighton beach drew an estimated 250,000 visitors on Sunday afternoon, with police closing the seafront approach roads for nearly two hours, and Network Rail reported buckled-rail speed restrictions on the South Western mainline between London Waterloo and Basingstoke that delayed roughly 40 percent of services. National Grid said electricity demand for cooling peaked at 38.4 gigawatts on Sunday afternoon, a record for May, with rooftop solar arrays generating nearly a quarter of total supply. Wildfire risk was rated "very high" across the New Forest, the Surrey Hills and the North York Moors, where two grass fires required helicopter water drops on Sunday evening.

Climate scientists were quick to put the numbers in context. Dr. Friederike Otto of Imperial College London, co-lead of the World Weather Attribution group, said preliminary analysis indicated a heat event of this magnitude in May would be "essentially impossible without human-caused warming" and is now expected roughly once every 15 years in the current climate, compared with once in several centuries before industrialization. "Every fraction of a degree of warming makes these spring heatwaves more likely and more severe," Otto said. "The U.K. is built for damp bank holidays, not 34-degree ones, and the infrastructure is showing it."