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 said storms could bring lightning, hail and flooding to some areas on Friday, with up to 50mm of rain falling in an hour. A yellow weather warning was issued for most of England, Scotland and east Wales from midday to 9am on Saturday. The south-west and parts of the south-east coast of England were not included in the warning. The Met Office meteorologist Craig Snell said: “Not everyone will see a storm, but if you catch one, you will certainly know about it.” The change in weather comes after the UK experienced its hottest day of the year so far on Thursday, when the mercury rose to 33.4C (92.1F) at Heathrow airport in west London. Thousands of people flocked 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 had their hottest days of the year so far, with the former recording 30.8C in Prestwick and the latter peaking at 31.4C in Trawsgoed, near Aberystwyth. Temperatures on Friday were forecast to reach 31C in London, the mid-20s for the rest of England and up to 27C in the Highlands, making for a relatively warm and humid day, Snell said. The storms were expected to clear north-eastwards in the afternoon and evening but would linger over north-east Scotland until Saturday morning. On Friday morning, the Environment Agency issued seven flood alerts, indicating flooding was possible, of which five were near rivers in the West Midlands, while others centred on the waterways around Loughborough, in Leicestershire, and the River Trent tributaries in Nottinghamshire. Temperatures were expected to drop on Saturday to 22-23C in London and stay around the high teens to low 20s in the rest of the UK. Snell said: “The weather will change but it will be more what people expect our summer to be like: a mix of sun and showers.” On Thursday, Bournemouth, Christchurch and Poole council declared a major incident after services were overstretched when huge numbers of visitors defied advice to stay away from its beaches. Condemning the “irresponsible” behaviour of crowds who gridlocked roads, dumped rubbish and parked illegally, the council said extra police patrols had been brought in. The local MP, Tobias Ellwood, told BBC Breakfast: “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. “The beach should have been closed down … to prevent further people from entering it.” The public has been advised to avoid cooling off in open water, after the deaths of two people 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 during the search for a missing man at Lulle Brook in Cookham, Berkshire. Eyad al-Ryabi, a Syrian refugee, had gone into the water on Tuesday evening to help a friend, his cousin said. The friend survived and was taken to hospital in a serious condition, Thames Valley police said. Meanwhile, the AA advised drivers to check their tyre pressures and coolant levels before leaving home after an increase in heat-related breakdowns. Its 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.”