However, temperatures are still expected to be relatively warm in Lancashire, with peak temperatures of around 22C on Saturday and 20C on Sunday.
Meanwhile, London's fire chief has called for barbecue bans to be imposed in the capital's parks after a record-breaking number of grass fires.
There have been instances of patients and visitors have vomiting and passing out, with temperatures on some wards exceeding 30℃, according to the RCN, which also noted that some nurses were not allowed to take water bottles on to wards.
In the west, Glasgow is already cloudy, with maximum temperatures of around 22C.
A yellow weather warning has been issued for Yorkshire and the Humber, including Sheffield, as thunderstorms are expected to hit between 2pm and 11.45pm on Friday (July 27).
Lincolnshire is now in the yellow and amber warning zones Met Office
Britons are sweltering in a prolonged heatwave, with temperatures set to test national records, the Meteorological Office says. Heavy rain and thunderstorms in the small hours of tomorrow will continue to bring the temperature down, making for a slightly cooler and rainy weekend in the capital, with some sunny intervals.
"25-30 mm of rain is possible in less than an hour but the vast majority of sites will miss these thunderstorms and see very little, if any, rain".
"Large hail, frequent lightning and strong, gusty winds will be additional hazards - however, many places will see much lower rainfall amounts".
SCOTLAND is on track for one of its driest summers for 108 years - as an African roast blows north to deliver a sizzle pushing 27C (80F) this week.
But the wet weather and cooler temperatures will just be a temporary respite as the mercury will likely rise again.