Thunderstorms and torrential rain are forecast to sweep across the UK, bringing an end to a week of blazing sunshine and scorching temperatures.
The Met Office has warned Friday’s storms could bring lightning, hail and flooding to some areas, with up to 50mm of rain falling in an hour.
A yellow weather warning is in place for most of England, Scotland and east Wales from midday to 9am on Saturday, and parts of Northern Ireland from 1pm until 10pm on Friday.
The south-west and part of the south-east coast of England are not covered by the warning.
Met Office meteorologist Craig Snell told the PA news agency: “Not everyone will see a storm, but if you catch one, you will certainly know about it.”
The change in weather comes as the UK experienced its hottest day of the year so far on Thursday, with the mercury rising to 33.4C (92.1F) at Heathrow Airport in west London.
The heatwave saw thousands of people flock to the south coast, resulting in a major incident being declared and Government experts warning people against gathering in large groups.
Scotland and Wales also experienced their hottest days of the year so far, with the former recording 30.8C (87.4F) in Prestwick, and the latter seeing temperatures rise to 31.4C (88.5F) in Trawsgoed, near Aberystwyth.
Temperatures on Friday are forecast to reach 31C (87.8F) in London, the mid-20s for the rest of England and up to 27C (80.6F) in the Scottish Highlands, making for a “relatively warm and humid” day, Mr Snell said.
The storms are expected to clear northeastwards on Friday afternoon and into the evening, but will remain over north-east Scotland until Saturday morning, the Met Office said.
On Friday morning, the Environment Agency issued seven flood alerts – meaning flooding is possible – of which five were focused near rivers in the West Midlands, while others were for the waterways around Loughborough in Leicestershire and the River Trent tributaries in Nottinghamshire.
Temperatures are expected to drop on Saturday to 22C to 23C (73.4F) in London, and stay around the “high teens to low 20s” for the rest of the UK, Mr Snell said.
He added: “It (the weather) will change, but it will be more what people expect our summer to be like – a mix of sun and showers.”
Earlier on Thursday, Bournemouth, Christchurch and Poole council said it was left with no choice but to declare a major incident after services were “completely overstretched” as huge numbers of visitors defied advice to stay away from its beaches.
Condemning the “irresponsible” behaviour of crowds who gridlocked roads, dumped rubbish, abused refuse collectors and parked illegally, the council said extra police patrols have been brought in.
Local MP Tobias Ellwood, speaking from Bournemouth beach on Friday morning, said: “This place was deluged and social distancing went out the window and that’s why a major incident was declared, because the local authority and indeed the police couldn’t cope.”
He told BBC Breakfast: “The beach should have been closed down, or at least shut down to prevent further people from entering it.”
There have been warnings not to be tempted to cool off in open water, following the deaths of two people in recent days in Berkshire and Scotland.
A 10-year-old boy died after getting into difficulty in Loch Lubnaig, near Callander in the Highlands, on Wednesday evening, Police Scotland said.
Meanwhile, a body was found following a search for a missing man at Lulle Brook in Cookham, Berkshire.
A cousin told the PA news agency that Syrian refugee Eyad Al Ryabi had gone into the water on Tuesday evening to try to help his friend.
The friend survived and was taken to hospital in a serious condition, Thames Valley Police said.
Meanwhile, the AA has urged drivers to check their tyre pressure and coolant levels before leaving home following an increase in heat-related breakdowns.
AA president Edmund King said: “With the combination of the severe heat, cars that have been in lockdown and millions of vehicles that have delayed their MoTs, the AA has seen more breakdowns.”