Potentially 'record-breaking' June temperatures
Ben Birchall/PA WireWarm temperatures in June "are potentially going to be record-breaking", according to a Met Office meteorologist.
The UK Health Security Agency (UKHSA) upgraded an amber heat health alert to red for Devon and Cornwall, which is in force until 23:00 BST on Thursday.
Alex Deakin, from the Met Office, said the length of the warm spell was "very unusual" - adding the "exceptional" temperatures would reach the mid to high-30s in some areas.
BBC broadcast meteorologist Bee Tucker said a heatwave was "likely" in the South West by the end of Wednesday, with temperatures likely to reach 30C and 35C (86F and 95F) respectively in Cornwall and Devon.
Deakin said: "It's really unusual, we're likely to push if not break records for June, even in Cornwall, but certainly across the rest of the UK."
He urged people to follow water safety rules and warned of cold water shock.
He said the UKHSA heat alert focused on a health impact where as the Met Office issued extreme heat warnings for when temperatures were "pushing records".
He said temperatures would vary across Cornwall due to the coast.
He added inland areas were set to be in the mid-30s on Tuesday and Wednesday, while coastal areas would be in the high-20s.
Deakin said there was a "big contrast" between land and sea temperatures.
"The sea is still warming up, it is quite chilly," he said. "Please only go to a lifeguarded beach if you can...cold water shock is a real thing," he said.
'Don't push yourself'
Sarah Bird, lead consultant in health protection at UKHSA South West, said it was "vitally important" people understood the risk associated with the high temperatures.
A red heat health alert indicated "a risk to life for even the healthy population," she said.
She said: "Simple actions like staying hydrated, avoiding the sun during the hottest part of the day, and keeping your home cool can make a big difference."
Bird urged health and social care services to be prepared.
"It's also important to look out for others, especially elderly relatives, neighbours, and those with underlying health conditions, to make sure they are aware of the forecast and following the necessary advice," she added.
In a post on X, Cornwall Council said its waste and recycling collections would begin earlier on 23 and 24 June due to the temperatures.
It urged people to put recycling, food waste, rubbish, garden containers and clinical waste out by 06:00.
Woolacombe Surf Life Saving Club coach Luxy Allix urged people to avoid staying in cold water for too long.
Allix said: "Unfortunately, we had those deaths recently in the last heatwave due to water shock. People do need to be really aware of that.
"Don't push yourself, don't go in too long and get really cold. Come out, warm up and then go back in."