Amber heat health alerts have been issued across parts of England as forecasters warned of a heatwave more severe than the one in May.
The warnings cover London, the south-east, south-west and east of England, and are in place from Thursday afternoon until 8pm on Tuesday June 23.
According to the UK Health Security Agency (UKHSA) website, the warning means an “increased demand” is likely to be placed on health and social care services, and could result in a rise in deaths.
Those aged 65 and over, as well as those with health conditions, will be most vulnerable, it said, though there may also be impacts on younger age groups.
Less severe yellow health alerts cover the east and west midlands, warning of minor impacts on services.
It comes as forecasters have predicted the incoming heatwave could feel even hotter than that experienced in May, with temperatures likely to push into the mid 30s.
As conditions turn “humid and muggy”, the south of England could see hights of 32C on Sunday – and even higher temperatures on Monday, the Met Office said.
Met Office meteorologist Honor Criswick said: “It’s a bit different to the last heatwave, because last time the humidity wasn’t as high, whereas this time the humidity is quite a bit higher.
“It’s just going to make it feel that bit muggier and that bit more humid during the day and overnight as well, so it just means it’s going to be more uncomfortable, the heat itself.”
She added: “Because the humidity is so high, there’s a chance that this could potentially spark off some thunderstorms.
“It’s always tricky with thunderstorms, because they could pop up pretty much anywhere, particularly across central, southern, south-east parts of England.
“But wherever they do hit, it’s probably going to be quite an intense, heavy downpour for a time with some rumbles of thunder, some sparks of lightning, but exactly where they’ll be is a tricky one to forecast at the moment.”
While it is not yet known when the heat will subside, it is likely to be prolonged over the weekend and for at least the first part of next week, Ms Criswick said.
Much of central and western Europe is also feeling the heat, with temperatures climbing well above average in places, helping to feed warmer air towards the UK, the Met Office added.
The AA has advised drivers to check tyres, oil and coolant levels, pack water for passengers and pets, and avoid driving during the hottest part of the the day – especially if using an older car.
A spokesperson added: “A parked car can become dangerously hot in minutes, so never leave children, older or vulnerable passengers, or pets inside a vehicle, even briefly.
“If you do break down, stop somewhere safe, if possible, keep well away from moving traffic and wait in the shade, in a safe place, while help is on the way.”
According to the forecaster, a heatwave is defined as three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold.
A record-breaking heatwave last month saw May 26 become the hottest May day on record for both England and Wales, with 35.1C recorded at Kew Gardens and 32.9C at Cardiff Bute Park.
The Met Office has warned people heading to the coast should be careful with sea-surface temperatures, which are not as high as they would be in mid-summer.
There was a spate of water-related deaths during the last heatwave, as many took to the water amid scorching temperatures, with as many as 15 fatalities recorded.
