Weather forecasters have warned that heavy rain, thunderstorms and hail could bring flooding to parts of Britain.
The Met Office has issued a severe warning of heavy rain for London and the South East, South West England, the East, Yorkshire, the Midlands, Wales and Grampian.
Up to 1.5 inches of rain could fall within an hour in some areas, forecasters warned.
Met Office forecaster Emma Sharples told the Daily Mail: "Heavy rain has moved up from the south overnight and by 9am it will be over the north of England and Wales – though there will still be thundery showers over the south as well.
"It has been caused by weather fronts that have started to move in from the south and the west, which have combined with low pressure and the warm temperatures over the continent."
The next few days are set to be unsettled, with more showers predicted.
Speaking to AOL Travel, chief forecaster at The Weather Channel, Leon Brown, said: "Saturday looks a rather wet day for Central to Northern England. Some heavy rain is expected early in the day moving from East Anglia and the Midlands to North Wales and the North of England, followed by a lot of heavy showers with local downpours, hail and thunder. 20 to 25mm of rainfall is likely quite widely but it will be drier over Scotland with just a few showers."
Leon says that Sunday will be Scotland's turn to see the heaviest showers with 15 to 25mm of rainfall likely over the east of the country. "There is likely to be some more heavy showers over central to northern England in the afternoon too but East Anglia and the South East may miss most of the showers. Temperatures will be in the 15 to 18C range."
There's better news for Bank Holiday Monday with a fine and quite sunny start for England and Wales. Mr Brown says that scattered showers will develop over South Wales to South West England by the afternoon, with the threat of some rain late in the day reaching the South East. But it will be a mild 17 to 20C.
For the rest of next week, there is likely to be more unsettled weather across the South as another area of low pressure develops, while the best of the weather is expected over the North West of Britain with shelter from the prevailing East to North East flow. Leon adds: "Temperatures will be near average and perhaps a little above over the West to North West of the UK until mid-week, in the 18 to 21C range."
Places you won't believe are in the UK
UK weather: Flood risk as heavy rain, hail and thunder on the way
No, it's the Vale of Glamorgan, Wales
Wales has a number of working vineyards and Llanerch Vineyard, located in the heart of the Glamorganshire countryside, is particularly picturesque. At first glance, the working vineyard appears as a scene straight out of France or even Australia. The site also holds a restaurant, bistro, boutique hotel and cookery school.
No, it's in Cardiff, Wales
Nineteenth century high gothic Castell Coch was built when 'eccentric genius' William Burges was given free rein by his paymaster, John Patrick Crichton-Stuart, the third marquess of Bute, to create a rural retreat to complement his main residence, Cardiff Castle. He didn’t hold back and created the fascinating residence, reminiscent of a Polish castle, with dazzling ceilings and over-the-top furnishings.
No, it's Liverpool, England
Chinatown in Liverpool is home to the oldest Chinese community in Europe and features the largest, multiple-span arch of its kind outside of China. Located near Liverpool Cathedral, Chinatown has an array of reputable Chinese restaurants, Chinese takeaways and a huge selection of Chinese groceries from many Chinese supermarkets.
No, it's Gwynedd, Wales
Portmeirion was designed in the style of a rustic Italian village in 1925 by Sir Clough Williams-Ellis, who wanted to show how a naturally beautiful site could be developed without spoiling it. The village was built as a place where events, concerts and exhibitions could take place, with 70 acres of exotic woodlands and coastal walks surrounding it.
No, it's Barra, Scotland
Beautiful Barra is the most southerly of the inhabited islands in the Outer Hebrides and boasts Caribbean-like beaches and waters.
No, it's the West Highlands of Scotland
A ride across the Glenfinnan Viaduct will make you like you’re in the magical world of Harry Potter as you cross the viaduct on the steam train. Built entirely out of concrete, the viaduct has 21 arches and is 30 metres high, offering breathtaking views over Lochaber’s Loch Shiel.
No, it's London, England
Piccadilly Circus is one of London's most iconic sites with its famous advertising hoarding, statue of Eros and many shops. The busy junction is popular with tourists who like to stop and take photos in front of the illuminated adverts, similar to those in the brightly lit Times Square in New York.
No, it's Brighton, England
The Royal Pavilion in Brighton is an exotic palace built for the Prince Regent, later King George IV, between 1787 and 1823. The extravagant building was heavily influenced by Chinese and Indian architecture of the time is as impressive inside as out and reflects the vibrancy of Brighton.
No, it's Cornwall, England
Looks just like an ancient Greek site overlooking the Aegean, right? Cornwall's Minack Theatre is an open-air theatre, where stone arches are used as scenery and the sea as the backdrop. The cliffside theatre in Porthcurno hosts summer shows and features landscaped gardens with stunning sea views for day visitors.
No, it's Cumbria, England
This epic wall built by the Roman Emperor Hadrian in AD122 took soldiers six years to complete and is 73 miles long from sea to sea. Hadrian's Wall is surrounded by wild countryside and scattered with Roman forts, temples and milecastles. The wall, along with the Great Wall of China, was declared a World Heritage Site in 1987.