Heavy rain will see parts of Britain already battered by Storm Angus at risk of further flooding in the next 24 hours.
Wet weather is expected to sweep across the South West and move north, causing damage and disruption as it falls on already saturated ground.
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.
Motorists are being warned not to drive through flood water and residents in at-risk areas have been advised to contact their local councils for sandbags to protect their homes.
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. The Met Office has extended the amber alert to include Somerset, meaning the county should be prepared for transport to be affected while the flooding of homes and businesses is "possible".
Exeter had already faced more than two inches (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 two inches (60mm) of rain forecast to fall in some places.
Alison Baptiste, national flood duty manager at the Environment Agency, said: "Large parts of southern England have already experienced the impacts of Storm Angus this weekend.
"With more heavy rain on its way, people in the North and South West need to be prepared for the risk of flooding."
Storm Angus, the first named storm of the season which moved off into the North Sea by about midday on Sunday, brought gusts of more than 80mph and caused power cuts for more than 1,000 homes in the South West.
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.