Wet weather is expected to hit the south west before moving north, causing damage and disruption as it falls on areas already battered by Storm Angus.
The Environment Agency said it is preparing to put up temporary defences "where necessary" and said rivers have been cleared to make sure water can flow freely.
An amber "be prepared" warning has been issued for Devon, where the worst of the rain is expected to hit in the early hours of Monday.
Exeter had already faced more than 54mm of rainfall overnight into Sunday - more than half of what is usually expected in the area for the entire month of November.
The West Midlands, Wales and north of England are all covered by a yellow "be aware" warning, with more than 60mm of rain forecast to fall in some places.
Alison Baptiste, national flood duty manager at the Environment Agency, said: "With more heavy rain on its way, people in the north and south west need to be prepared for the risk of flooding.
"People should remember not to drive through flood water and be aware travel may be disrupted.”
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Storm Angus has brought gusts of more than 80mph and caused power cuts for more than 1,000 homes in the south west.
Fire crews in Devon spent Sunday pumping out flooded properties and roads, and warned many of those same areas are due to be hit by wet weather again.
Devon and Somerset Fire and Rescue Service station manager Martin Bayet said there is likely to be surface water on country roads so motorists should be wary of the possibility of floods, take notice of road closure signs and not attempt to drive through flood water.
Wind speeds of up to 50mph are expected on Monday and the persistent downpours in the south west early on in the day are likely to be followed by thundery showers, the Met Office warned.
RAC traffic spokesman Rod Dennis said: “Large parts of the UK continue to experience very wet weather, with Met Office warnings in force across the north and west of the country. With saturated ground, road conditions are likely to remain difficult at least until the end of the day.
"Our advice is for motorists to check for disruption on their routes before they set out, listen to local radio for traffic updates while driving, and be prepared for delays and diversions caused by floodwater.
"Switch on dipped headlights and reduce your speed significantly to improve the chances of stopping safely.
"Where possible avoid driving through standing water which can cause your vehicle to aquaplane, and never drive through water if you can’t be sure how deep it is – if in doubt, turn around and find another safer way to your destination.”
November has brought drivers wintery weather and motorists have already been urged to take care of potential snow storms this month.