Yellow weather warnings for rain and wind are in force every day until Thursday as a newly named storm approaches the UK.
Storm Ciaran is set to bring strong winds and heavy downpours to southern parts of England and Wales - with "unsettled" conditions forecast for much of the UK.
Met Office yellow warnings are in place, but they are likely to be escalated in the coming days once confidence in the modelling improves.
Met Office deputy chief meteorologist Chris Almond said: "Winds associated with Storm Ciaran are likely to gust to 80mph along the south coast of England, with a small risk of somewhere exposed seeing 90mph, and winds could even gust up to 50mph or 60mph further inland."
He added: "This deep low-pressure system will also bring heavy rain to much of the UK, but the heaviest rain is expected in southern and western areas with 20 to 25mm quite widely across the region but up to 40 to 60mm potentially over higher ground.
"Heavy and persistent rain will fall on to already saturated ground bringing a risk of further impacts such as flooding in areas that are already struggling to clean up from the heavy rainfall we have seen over the last week or so."
Sky News weather producer Joanna Robinson said a deep area of low pressure is set to move in on Wednesday night - and weather warnings could be escalated over the coming days.
There is an increased risk of fallen trees because of saturated ground - with fresh flooding in areas already struggling to clean up after heavy rainfall.
ScotRail services will be returning to normal after speed restrictions were introduced while a yellow weather alert was in force in much of eastern and northeast Scotland.
The company's service delivery director, David Simpson, said: "The vast majority of services will operate as normal on Monday, and we look forward to welcoming passengers to take advantage of our off-peak all-day trial.
"Our first priority is always the safety of customers and staff, and we only run services when we are absolutely sure the lines are safe.
"We thank customers, especially those in the north of the country, for their understanding and patience following the extreme weather."
Some communities could be cut off by flooded roads on Thursday, and the Met Office said fast flowing, and deep floodwater could cause a danger to life.
Yellow warnings for rain affect southern areas of Northern Ireland, southern Wales, the north and east of Scotland, and the northeast and southeast of England.
The Met Office indicates the rainfall could affect transport networks and bring down power supplies.
Read more: Why Storm Babet brought so much rain
The Environment Agency has issued 72 flood warnings across the UK, but largely focussed on the south coast.
It warned of "significant coastal flooding", with a further 175 alerts in place.
Flooding has already occurred over the weekend with a deluge of rain in Sussex closing shopping centres and holiday parks.
Kate Marks, flood duty manager at the Environment Agency, said: "We urge people to stay safe on the coast and to remember to take extreme care on coastal paths and promenades. Flooding of low-lying coastal roads is also possible and people must avoid driving through flood water, as just 30cm of flowing water is enough to move your car."
The warnings arrive in the aftermath of Storm Babet, which flooded large parts of the UK and left some homes and businesses underwater.
Seven people are known to have died during Storm Babet, including three in Scotland.