Heavy rain is forecast in Devon, Cornwall and much of the south of England - raising fears of more flooding over the weekend.
The Met Office has extended a yellow warning for rain after Storm Ciarán brought flooding and damage.
The Environment Agency (EA) said rivers would rise "really quickly" as the ground was already saturated by rain.
It urged people to sign up to the EA's flood warning service and check their area.
The Met Office warned: "Flooding of a few homes and businesses is possible.
"Large waves may lead to dangerous conditions across some English Channel coastlines."
Clarissa Newell, from the Environment Agency in the South West, said: "When the catchments are full of water like this it's really important to know that it will rise very quickly.
"You can think you're having a bit of rain then suddenly it's coming in through your door."
In this situation, she warned people turning off electricity and gas, and moving to safety, and "bringing important documents with you", was key.
Bee Tucker, BBCSW broadcast meteorologist, said: "Some places have had close to 50mm (2ins) of rain since the start of the month, almost a third of the average rainfall for November.
"Some of the heaviest showers could give 20mm (0.8in) of rain and some places could get all their monthly average rainfall by the end of play on Sunday."
Across the British Isles, the clean-up after Storm Ciarán continued on Saturday, after roofs were blown off homes and some train lines completely ground to a halt.
In Hampshire, families in more than 18,000 homes headed into the weekend without water or experiencing low pressure after the storm led to a supply works being shut down.
National Grid said on Saturday morning that all storm-related power cuts in Devon and Cornwall had been resolved, while Energy Networks Association (ENA) said nationally there were no outstanding outages.
Most railway services had also resumed on Saturday but the GWR line between Liskeard and Looe is expected to remain closed throughout the day, the operator said, as a result of "heavy rain and winds over the last 24 hours".
A bus replacement is operating and tickets for travel on Saturday can be used on Sunday.
Meanwhile, Cornwall Council said work on the clean-up after Storm Ciarán would continue into the weekend, after its highway team responded to more than 400 incidents, with all fallen trees now cleared.
Pondhu Primary School in St Austell, Cornwall, remained shut on Friday due to extensive flooding, with the school saying it needed time to "dry and clean the building so the children can return safely".
Councillor Martyn Alvey, who responsible for the environment at Cornwall Council, said: "Our next concern is surface water flooding that is possible as a result of the rain on saturated ground.
"I would say that every community that knows they have a vulnerability to flooding should be on alert.
"We are not going to have the same issue we had last weekend with spring tides locking in those coastal villages but some of them will still have trouble from the river that feeds through the village and into the sea.
"We are ready to respond as required.
"Unfortunately, the nature of weather as it hits Cornwall is you can never know exactly which community is going to be hit so it's a case of deploying resources as the incidents come in."