The Met Office has issued a yellow weather warning for thunderstorms and heavy rain across parts of Wales and five English regions, valid until 4 a.
m. Thursday.
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The warning follows record-breaking May temperatures.
Forecasters warned that severe downpours, hail, and spray could disrupt drivers, damage buildings through lightning strikes, delay public transport, cause localized flooding, and trigger short-term power cuts.
The severe weather developed after Kew Gardens reached 35.1°C and Cardiff Bute Park hit 32.9°C on Tuesday.
These are the hottest May days ever recorded for England and Wales.
Health Alerts Extended
Amid the soaring temperatures, the UK Health Security Agency extended amber heat health alerts for London, the East of England, the South East, the South West, and the East and West Midlands until 5 p.
m. Thursday.
The North West and North East remained under yellow alerts.
The extreme heat caused a massive surge in public inquiries for medical advice, according to NHS England data.
The NHS heatstroke advice webpage received 20,092 visits on bank holiday Monday, compared to 488 the previous Monday.
Total weekend hits reached 36,724.
The NHS also recorded 10,314 total weekend visits for sunburn advice.
Traffic to baby first aid and sun safety pages surged nearly 3,500 percent on Monday, drawing 4,728 hits.
Duncan Burton, Chief Nursing Officer for England, said many new parents sought advice on keeping babies safe in the sun.
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He noted that while temperatures are beginning to drop, health alerts remain active across multiple regions until Thursday evening.
Burton urged people to stay vigilant, especially when caring for vulnerable individuals.
Babies, children, older people, and those with long-term conditions like diabetes or heart problems are at higher risk of heat exhaustion or heatstroke.
Medical authorities emphasized that dehydration and heat exhaustion can quickly escalate into life-threatening heatstroke if left unmanaged.
The NHS website offers information for different age groups to help keep loved ones safe and avoid dehydration.
Fatalities in Open Water
Alongside heat illnesses, emergency services reported multiple fatalities in open water across South Yorkshire, West Yorkshire, Devon and Cornwall, Warwickshire, Lincolnshire, and Lancashire.
Cheshire Police confirmed that underwater search teams, a police helicopter, and fire crews recovered the body of a 17-year-old boy on Wednesday after he went missing in Pickmere Lake at Marston.
Chief Inspector Jamie Lewis warned that while warm weather tempts people to cool off in open water, hidden currents and unseen dangers such as mud banks or submerged objects can be deadly.
Similar tragedies occurred nationwide, including the recovery of a teenage boy's body at Hawley Lake after a multi-agency search began on Tuesday afternoon.
Other recent incidents include the deaths of 15-year-old Declan Sawyer at Swanholme Lakes, 13-year-old Reco Puttock at Leadbeater Dam, and a teenage girl at Kingsbury Water Park.
A man in his sixties suffered a fatal cardiac arrest at Tregirls Beach while rescuing two family members on Monday.
A teenager's body was recovered from Rother Valley Country Park early Tuesday, and a 12-year-old boy died Tuesday evening in the River Ribble.
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The RNLI warned that despite record-setting air temperatures, low water temperatures present a very real risk of cold water shock for open water swimmers.
