Parts of the UK are set to be hit by heavy downpours with up to 70mm (2.7 inches) of rain forecast from Monday evening.
The Met Office has issued a yellow weather warning for rain for areas of southern England and South Wales, including Hampshire, Oxfordshire, Gloucestershire, Cardiff, Devon, and Cornwall.
The warning, which runs from 6pm on Monday to 3am on Tuesday, means rain will become persistent and heavy, with car, bus and train journey times set to take longer and power supplies and other services likely to be affected.
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Most of the affected area will see up to 40mm (1.6 inches) of rain, with the highest levels expected in places such as Dartmoor and Exmoor.
Northern Scotland will bear the brunt of the unseasonal conditions from late on Tuesday through Wednesday when forecasters have predicted up to 90mm (3.5 inches) in the worst affected areas.
A second yellow weather warning is in place from 10pm on Tuesday until 11.59pm on Wednesday and covers areas including Angus, Aberdeenshire, Moray, and the Highlands.
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Some communities could be cut off due to flooded roads, the Met Office has warned, and driving conditions may become difficult because of flooding and spray, while fast-flowing or deep floodwater could cause a danger to life.
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The weather agency said anyone planning to use public transport should be ready for delays and cancellations as 20-30mm (0.8-1.2 inches) of rain falls across most of the affected area.
But 50-75mm (2-2.8 inches) could fall in places that suffer localised heavier bursts.
And up to 90mm (3.5 inches) is possible across Grampian and the northwest Highlands.
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Met Office spokesperson Andrea Bishop said: “The first half of this week is unsettled – wet and cool is a trend to hopefully some better conditions by the weekend, although you’ve still got sort of sunny spells but with showers in places.”
Central England is expected to enjoy the UK’s warmest weather this week with temperatures of up to 24C (75F) on Tuesday, while the country’s coldest temperature of 3C (37F) is forecast in rural Scotland on Thursday evening.
