High pressure could bring temperatures to record-breaking levels by Sunday, with forecasters closely watching whether London will meet the official heatwave threshold for the first time this year.
Temperatures in the capital are predicted to climb sharply from Friday, with some models suggesting highs of 28°C in Greater London and Cambridgeshire on 22 May. That would make it the hottest day of 2026 so far, surpassing the 26.6°C recorded at Kew Gardens on 8 April. Saturday could push even higher, with the south-east of England potentially reaching 29°C and isolated spots touching 30°C in the south and south-east. By Sunday, London is again expected to hit 30°C, while much of the rest of the south-east sees highs around 26°C.
The significance of these figures lies in the Met Office’s definition of a heatwave: three consecutive days above a county-specific threshold. For London, that threshold is 28°C. If temperatures remain elevated through Friday, Saturday and Sunday, the city would officially record its first heatwave of the year. The current spell follows a period of unusually cool and unsettled weather, with temperatures having been below average for much of May.
The May record for the highest temperature in the UK stands at 32.8°C, set in London in 1944. Meteorologists believe the current forecasts could approach that mark, though the likelihood remains uncertain. Beyond the capital, large swathes of England are expected to see highs between 22°C and 25°C on Friday, rising to between 20°C and 25°C on Saturday, and between 21°C and 27°C on Sunday. Northern areas and Scotland are likely to stay cooler, with more cloud and occasional rain – a typical north-south divide when high pressure settles over southern England.
How the pressure system is driving the warm spell
The driver of this prolonged warm period is a significant area of high pressure building from the south. Forecasters say this system is expected to remain in place for at least the first half of next week, drawing warm and increasingly humid air up from southern Europe. Met Office data indicates that this pattern could sustain dry, settled conditions across much of the UK well into the Bank Holiday week.
By Bank Holiday Monday, temperatures could again reach 30°C in the south, with slightly cooler conditions further north. Tuesday may bring another 30°C day for London. Some longer-term forecasts suggest a possible spike to 32°C by Thursday 28 May in London, with other parts of the country seeing 30°C. The Met Office’s three-month outlook points to a 40% chance of a “hot” summer from May through July 2026, and there is potential for record-breaking highs that could reach 40°C by July and August – a stark reminder of the climate context in which extreme heat is becoming more frequent.
Reports indicate that by mid-century, UK heatwaves could regularly exceed 40°C, and the risk of homes overheating is rising. Extreme heat is already considered the most immediate climate-related threat to life in Britain. The current event, while not at that level, will test how buildings, offices and retail spaces perform in warmer conditions; an ongoing survey is assessing UK building preparedness for heatwaves.
Uncertainty remains over whether the threshold will be reached
Despite the strong signal for hot weather, forecasters are cautious. Ms Murray, a forecaster tracking the system, said: “If temperatures hold up on Saturday, we are expected to keep high pressure around into at least the first half of next week, so there is a potential that we may see those thresholds reached by the time we get to Sunday but… it’s not 100% certain on that yet.” The possibility of thundery showers, particularly on Saturday, could disrupt the heat build-up, and the Met Office has warned of “unsettled” weather at times even as temperatures climb.
A broader climatic influence is also at play: a “Super El Niño” event is affecting global weather patterns, increasing the likelihood of warmer-than-average conditions in the UK but also raising the risk of heavy rainfall and flooding later in the season. This year’s warm spell, however, remains a short-term phenomenon with public health implications already being flagged. The most vulnerable groups – older people, young children, pregnant individuals, those with pre-existing health conditions, and people who spend a lot of time outdoors or in hot environments – face risks including dehydration, overheating, heat exhaustion and heatstroke.
Health authorities advise staying indoors or in the shade between 11am and 3pm, avoiding strenuous outdoor activity during the hottest parts of the day, and drinking plenty of fluids while avoiding alcohol, caffeine and sugary drinks. Light-coloured, loose-fitting clothing, a hat and sunglasses are recommended, along with sunscreen of at least SPF 30. Homes can be kept cool by closing blinds and curtains during the day and opening windows at night; electric fans are effective only if temperatures are below 35°C. People are urged to check on vulnerable friends, family and neighbours.
Infrastructure could also come under strain. Hot weather can put pressure on water and energy networks, transport systems, and health and fire services, potentially causing power cuts, water supply issues and transport disruption. Local authorities and utilities will be monitoring the situation closely, but for now the focus remains on whether London will string together three days above 28°C by Sunday – a milestone that would confirm the arrival of the year’s first official heatwave.
