Thunderstorms are expected to cause flooding, lightning and power outages across parts of the UK, with warnings of road and transport disruption.
The Met Office has issued an amber warning for thunderstorms stretching from Norwich in East Anglia to Brighton on the south coast, including London, Chelmsford and Canterbury.
The warning is in place from 4pm to 9pm on Monday, with the Met Office saying thunderstorms and heavy rain may cause travel disruption.
Forecasters warned of sudden flooding which could lead to difficult driving conditions and road closures, as well as power cuts and flooding of homes and businesses.
“Flooding of homes and businesses is likely and could happen quickly, with damage to some buildings from floodwater, lightning strikes, hail or strong winds,” the Met Office said.
A yellow weather warning for rain is also in place which covers central and southern parts of the UK stretching from Brigg in North Lincolnshire to Weymouth in Dorset and Canterbury in the South East.
People in those areas have been warned of heavy rain and a small chance of flooding and disruption.
The warning is in place from noon to midnight, with between 0.6in (15mm) and 1in (25mm) of rain expected to fall across the area.
Up to 2.4in (60mm) of rain could fall in isolated areas within the warning area, the Met Office said.
“We have an unsettled week with quite a lot of rain,” spokeswoman Nicola Maxey told the PA news agency on Monday.
“There’s a warning out for quite a lot of rain to come through today, especially for the southern and central areas, where it will be heaviest.”
The Environment Agency has issued three flood warnings for the River Avon in the South West, near Bristol and Bath.
As of 1.45pm, the agency had 42 flood alerts in place across the South West, Midlands and parts of Yorkshire.
Parts of the UK have already seen more than half of their average monthly rainfall, the Met Office said.
Norfolk in East Anglia has been drenched, with 91% of the county’s monthly rain falling already.
In the South West, Wiltshire has also had a wet October, experiencing 89% of its average monthly rainfall so far.
The UK as a whole has seen 55% of its average monthly rainfall, which Ms Maxey said is not abnormal for this time of year.
“When you get into winter, you tend to see long spells of rainfall and it comes across the whole month and it’s more evenly spread, but we’re in that transition period,” she said.
The Met Office said Scotland, northern England and the West will remain mostly dry for the first few days of the week before another weather front brings downpours to those areas on Wednesday.
The low pressure system is forecast to start moving across the country on Wednesday night, with a chance of thunder in the West.
Strong winds and locally heavy showers are expected, particularly in the West from Wednesday to Friday.