Wednesday will be a “thoroughly wet day”, according to BBC forecaster Helen Willetts. Winds are set to bring 70mph gusts with a weather front that could become Storm Aiden.
Heavy rain could bring up to three inches of rain in areas of Scotland today.
The Met Office have issued a yellow weather warning for Wednesday for south west Scotland.
Heavy rain is expected to bring disruption to travel for Dumfries, Galloway and Strathclyde.
The Met Office said: “Heavy rain will arrive in the early hours leading to a very wet Wednesday morning. 25-35mm will fall quite widely in around 6-9 hours, with 40-50mm in a few locations.
“Despite the recent dry conditions, these totals will be enough to cause some surface water flooding, or flooding from smaller watercourses.”
If winds are powerful enough this week to spark an amber warning from the Met Office, Storm Aiden will be named as the first of the season.
Ms Willetts said: “Wet, windy and feeling cooler on Wednesday.
“Cooler weather still is on its way for the end of the week.
Aidan McGivern, Met Office Meteorologist, said: “Following a fine Tuesday for many of us, Wednesday will bring outbreaks of rain at times along with a freshening wind, gales around exposed western coasts.”
He added: “Quite a long strip of wet weather pushing into western Britain during Wednesday morning.
“Certainly, Northern Ireland, western Scotland, western parts of England and Wales seeing a lot of wet weather first thing.
“And that wind picking up as well around those western coasts 50mph gusts in exposed spots or perhaps more.”
By midday on Wednesday, most of Scotland and England will be drenched in wet weather.
Mr McGivern added: “Very heavy rainfall moving into southern England.”
Temperatures are set to drop from the mid-teens Celsius to the low-single figures this week in some parts of the UK.
By the end of the week, frost is expected in many parts of the north and west of Britain.
Mr McGivern said a low pressure moving is will get “deepened quite furiously by the jet stream which dives to the south of the UK”.
He added: “And by Friday it’s significantly deeper and it’s likely to bring a significantly wetter period of weather during Friday and much of the weekend for various parts of the UK.”