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 of rainfall and 60mph winds over the next 36 hours, with pockets of Scotland, northern England and the south west particularly susceptible to flooding.
The Environment Agency has already put out several flood alerts, and said further warnings are likely to be issued for river and surface water flooding elsewhere. People in the south west and south east of England are urged to prepare for possible flooding before going to bed on Sunday, it added.
Paul Mott, senior meteorologist at MeteoGroup, 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 Sunday and Monday night.
Members of the public are urged to check the Environment Agency website for the latest information at www.environment-agency.gov.uk/flood, or by calling the Environment Agency Flood Line on 0845 988 1188.