Amber and yellow weather warnings for severe rain and wind have been issued by forecasters at the Met Office for Friday.
Wales is set to experience a heavy spell of rain, with up to 40mm set to to fall from midday, creating the risk of fast-flowing or deep floodwater, which could cause “danger to life.”
The downpours are set to continue on Saturday across south west Wales from 6am until 11pm and there is a risk of hail and thunder too.
London, the south east, the south west, and parts of Scotland are set to be pelted with up to 50mm of heavy rain from 1pm. Strong winds with gusts of up to 70mph are also expected.
There is a risk of flooding to some homes and businesses and journey times are expected to be longer.
Met Office forecaster Alex Deakin said: “It’s going to turn pretty bleak out there by this afternoon… A big swirl of cloud out in the Atlantic is heading our way, already pushing its way into the west.
“There’s the rain, accompanied by ever-strengthening winds. Because we’ve had so much rain recently, especially across Pembrokeshire, that’s why we have the amber warning.
“It will actually be quite mild with temperatures in double figures but obviously it won’t feel all that mild, particularly as the wet and windy weather arrives.”