The persistent heavy downpours that have swamped much of the country will continue today and cause some areas to experience a whole month's rainfall in just 24 hours, weather experts say.
Communities across England and Wales are bracing themselves for the risk of floods from rivers and surface water as up to 100mm, almost four inches, of rain could fall by the end of the day, the Met Office said.
In England the Environment Agency has issued 55 flood warnings for the South West, the Midlands, Wales, the North East and North West, and 164 less serious flood alerts in the South East and East Anglia.
The Pennines are likely to receive the heaviest rain, leading to an increased risk of flooding for communities around the rivers Aire and Calder.
Strong winds are also expected to batter parts of Northern Ireland and Scotland, with gusts of up to 70mph along coastal areas later this morning.
A significant number of flood warnings could be issued over the coming days as the wet weather looks set to persist over the UK until the middle of the week.
Tom Tobler, a forecaster with MeteoGroup, the weather division of the Press Association, said Wales and northern England would see much of the heaviest rain today.
He said: "Further south and east, and in central and southern England, there will be some sunny spells.
"But there will be heavy showers coming in along the south coast and Kent. Places like East Anglia will be fairly dry, with just the odd shower.
"The heavy rain will be across the north west and north east, which have already had a lot of rain since yesterday, and there will be a risk of flooding.''
Mr Tobler said parts of England and Wales had experienced up to 50mm of rain up to 6pm yesterday, and a further 25mm to midnight, with 5mm falling every hour in many areas.
He said: "It is the persistent nature of the rain, rather than it being torrential, so it just adds up.''
The rain has already caused floods and travel chaos.
The Environment Agency is urging people to be prepared for flooding, keep an eye on local weather reports and sign up to its flood warning service. People are also being urged to stay away from swollen rivers and not to attempt to drive through floodwater.
Heavy rain yesterday led to more than 100 properties flooding, with some 42 properties in the South West, 35 in the Midlands and 20 in the South East hit by surface water floods.
There was widespread disruption and long delays to rail services in the South West, the Midlands, northern England and Wales, with the lines between Exeter and Bristol, and Wakefield and Leeds among those hit.
The AA said it had been called out to more than 200 vehicles driven through or stuck in floodwater.
Devon and Somerset Fire Service responded to dozens of reports of flooding, with water up to 3ft deep in some properties in Wedmore, near wells, Somerset.
Avon Fire and Rescue Service said people had to be rescued from cars in water and flooding in homes in Bristol, North Somerset and South Gloucestershire.
The heavy rain and flooding is the latest to hit parts of the UK this year, which saw drought in the spring give way to repeated downpours leading to the wettest April on record and the wettest summer for 100 years.