The UK's heatwave is predicted to come to a dramatic end this week, as forecasters say it will give way to three days of thunderstorms.
The Met Office has issued a yellow weather warning for thunderstorms in England, Wales, Scotland and Northern Ireland for Monday, Tuesday and Wednesday.
There are also predictions that the heavy downpours will lead to flooding, as ground dried by days of scorching temperatures may not be able to absorb large amounts of water.
Dan Stroud, a meteorologist at the Met Office, said the expected downpours will not alleviate the current 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.”
Mayor of London Sadiq Khan told Londoners to brace themselves for flash flooding this week.
“Speaking to the Met Office, the Environment Agency and many others, we are concerned that over the next few days we could see a huge amount of rain in a short period of time which could lead to flash flooding," he said.
“I have written to tens of thousands of Londoners who live in homes that could be affected by flash flooding."
Professor Hannah Cloke, an expert in hydrology at the University of Reading, said London could see flooding in the Tube if heavy rain hits the capital.
“If you get a heavy rain in a city, the drainage system can copy up to a point but if there is really heavy rain it can overwhelm the system – the rain cannot run away quick enough," she said.
“Water tends to find the lowest pathway – that is why it is so dangerous for cities with these surface area floods.
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“That is why it is of concern to the Tube and underground car parks and things like that."
She pointed out that flooding had affected London Tube stations last year.
Robert Caudwell, chairman of the Association of Drainage Authorities (Ada), said there is “very little” water management companies can do to prevent groundwater flooding.
“It’s been a really dry spell and the land is very hard, so any thunderstorms are unlikely to soak into the soil – they’ll run off the land very quickly,” he said.
Some places in the UK will still see temperatures of 31C and 32C on Monday, forecasters said, while other areas will be hit by thunder and lightning.
Power cuts and rail and bus cancellations are predicted, while spray and sudden flooding could lead to difficult driving conditions for motorists.
The yellow thunderstorm warnings applies to Scotland and Northern Ireland for Monday, and all of England and Wales on Monday and Tuesday, while it is in place on the south west and south east of England from Monday to Wednesday.
An official drought was declared in eight areas of England on Friday by the National Drought Group (NDG), which comprises representatives from the government, water companies, the Environment Agency (EA) and others.
On Monday, a hosepipe was announced in Cornwall for the first time in 26 years.
South West Water said the ban is being introduced in Cornwall and parts of Devon from 23 August.
“It’s the first time in 26 years but we’ve been left with no other choice. We need to have a hosepipe ban now to protect our precious water,” a company spokesman said.
“We’ve done our best to avoid this ban. We’ve increased the amount of water we can store, doubling it since the last drought in 1976."
Welsh Water, Southern Water, and South East Water have all imposed hosepipe bans, while Yorkshire Water has announced a ban will start on 26 August and Thames Water is planning one in the coming weeks.
Watch: Drought declared in parts of England