Communities across the country are braced for an abrupt end to the warm September sunshine after the Environment Agency prepared to issue dozens of flood warnings.
It comes as forecasters predict up to 60mm rainfall and 60mph winds over the next 36 hours, with pockets of the south west, northern England and Scotland particularly susceptible to flooding.
The Environment Agency has already put out several flood alerts, and today said further warnings are likely to be issued for river and surface water flooding elsewhere. People in the south west and south east are urged to prepare for possible flooding before going to bed tonight, they added.
Paul Mott, senior meteorologist at MeteoGroup, the weather division of the Press Association, warned: "There is going to be a big change in the weather from what we have had recently."
Parts of Britain have basked in warm temperatures in the mid-20s during September, a welcome break from the rain and wind which dogged much of July and August.
Mr Mott said: "Some parts of the country have enjoyed some very dry and warm days during September, with barely a couple of inches of rainfall.
"But, over the next 36 hours, quite a few areas are looking at 30 to 40mm of rain, with as much as 50 to 60mm locally.
"There is likely to be some localised flooding, and gusts of up to 60mph in parts of Scotland, which is enough to pull up the odd tree."
The Environment Agency told residents to be prepared for significant disruption, including to travel and flooding of properties and communities, between today and Monday night.
Its director of operations, David Jordan, said: "We are expecting flooding across the country from this evening and in to Monday and Tuesday.
"We strongly urge people to sign up to flood warnings, keep a close eye on local weather forecasts and be prepared for the possibility of flooding. We also ask that people stay safe, by staying away from swollen rivers and not attempting to drive through floodwater."
But Mr Mott said there was likely to be some respite as the week went on, particularly in southern England.
He said: "I think the worst of the weather will be over the next couple of days and will settle down in the south in time for the weekend."
Members of the public are urged to check the Environment Agency website for the latest information at http://www.environment-agency.gov.uk/flood (WEBSITE CORR) or by calling the Environment Agency Flood Line on 0845 988 1188.