Three days of rain and yellow weather warnings are forecast for the UK, bringing an end to the dry weather and weekend highs well into the 30s.
Despite most of the UK being under weather warnings, the most intense storms are expected first in Scotland and Northern Ireland before moving into England and Wales. Some southern areas may even remain hot and dry for a day or two longer.
Power cuts and delays and cancellations in trains and buses are predicted, while spray and sudden floods could lead to difficult driving conditions.
“First half of the week, we're looking at some heavy downpours and thunderstorms developing,” said Met Office meteorologist Greg Dewhurst.
“You can sort of see that sort of transition coming in from the north, it's day by day.
“It's still hot tomorrow, we're looking at highs around 31°C, possibly 32°C, and then it starts to come down. As we head towards Tuesday, temperatures are around 26°C or 27°C. Wednesday Thursday will be the mid 20s.”
In Scotland and Northern Ireland, a yellow warning for thunderstorms was in place from 9am on Sunday, with a sweep of heavy rain expected for the next two days.
The severe weather began to affect shops as customers were moved from a Tesco supermarket in Inverness when water poured in through the ceiling.
Videos on social media showed ceiling tiles falling and water pouring in, covering most of the floor in the supermarket on Sunday.
Second heatwave of the summer
The highest temperature at the weekend was recorded in Charlwood, Surrey, at 34.1ºC, said the Met Office.
Several wildfires erupted across England caused by the hot weather, with blazes breaking out in Yorkshire, Northamptonshire, Essex and Devon.
A search was made for a man in the River Thames in west London after he reportedly got into difficulty in the water.
An official drought was declared in eight areas of England on Friday by the National Drought Group, which includes representatives from the government, water companies and the Environment Agency.
Three water companies — Welsh Water, Southern Water, and south-east Water — have all imposed hosepipe bans, while Yorkshire Water said that a ban would start on August 26, and Thames Water is planning one in the coming weeks.
Mr Stroud said that despite the forecast for intense showers over the next few days, it is unlikely to help the drought.
“It will help a little but to be honest, really, it’s almost the wrong sort of rain,” he said.
“What we’re likely to see is some heavy, intense downpours. With the ground baked so dry, it’s very difficult for the ground to actually absorb the water very quickly.
“So what tends to happen in these circumstances is the water runs off and we can potentially get some surface run-off issues, so some flash floods.”
On Saturday, residents in Surrey were without water after problems at the Netley Mill Water Treatment Works.
Thames Water apologised and distributed bottled water to residents in Guilford, Surrey Hills, Dorking and Horsham while engineers worked to restore the supply.
By Sunday morning the problem had been fixed, with residents being told water was “gradually returning to the area”.
Just before 7pm, the company said the Netley Mill works were running normally.
“We are very sorry that customers have been affected, especially at a time of high temperatures,” Thames Water said.
“When supplies do begin to return, we are asking customers to try to use this just for essential use initially. This will help us return supplies to everyone quicker.
“We are supplying bottled water to customers who we know need additional help. If anyone is unable to travel to a bottled water site they should contact us on 0800 316 9800 and we will provide assistance.”