The Met Office has issued an amber extreme heat warning, with temperatures expected to hit more than 30C later this week.
The warning covers most of southern England and parts of eastern Wales, and will last from Thursday (August 11) through to the end of Sunday (August 14).
Met Office deputy chief meteorologist Dan Rudman said: “Thanks to persistent high pressure over the UK, temperatures will be rising day-on-day through this week and an extreme heat warning has been issued.
“Temperatures are expected to peak at 35C on Friday and Saturday, or even an isolated 36C on Saturday. Elsewhere will see temperatures widely into the high twenties and low thirties.
“Coupled with the high daytime temperatures, there will be some warm nights, with temperatures expected not to drop below the low twenties for some areas in the south.”
The Met Office warns of potential impacts on health, transport and infrastructure, with National Highways advising people to take plenty of water with them when travelling and to check their vehicles before heading out.
Dr Agostinho Sousa, head of extreme events and health protection at the UK Health Security Agency, said: “Temperatures will feel very warm again this week, particularly in southern and central parts of the country.
“We want everyone to enjoy the warm weather safely when it arrives, but remember that heat can have a fast impact on health.
“It’s important to ensure that people who are more vulnerable – elderly people who live alone and people with underlying health conditions – are prepared for coping during the hot weather.
“The most important advice is to ensure they stay hydrated, keep cool and take steps to prevent their homes from overheating.”
The mayor of London, Sadiq Khan, said he is “urging all Londoners to stay safe and vigilant in the hot weather”.
He added: “This heatwave, part of a pattern as a result of climate change, brings with it a potential threat to life so it’s crucial we all take sensible precautions to look after ourselves and help reduce the pressure on our emergency services who will be very busy at this time.”
The warning follows a heatwave earlier this summer, in which fires broke out across the UK as temperature records were broken.
The London Fire Brigade said July 21 was its busiest day since World War Two, with 1,146 incidents across the capital.
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