The Met Office has put a weather warning in place for south-west England, Wales and parts of the north.
Areas of the UK will be battered by winds of up to 40mph on Friday.
Forecasters predict the weekend downpours, which in some places will exceed a “month’s-worth of rain”, will “become widespread and heavy at times” throughout Friday.
But conditions are expected to warm up shortly after.
The yellow weather warning is in place from 8am on Friday until 10pm that evening.
The Met Office has said the wet weather will cause disruption to those travelling on road and public transport.
It also said flooding of homes and businesses is also possible in some areas.
A summary read: "Rain is expected to become widespread and heavy at times during Friday. Heavy rain may also coincide with peak travel times during the afternoon and early evening leading to difficult driving conditions on major routes.
"The heaviest rain is most likely over high ground, where some places may see 60-80 mm. Strong winds are also expected with 30-40 mph gusts likely around exposed coasts and hills."
The gloomy weather will carry on through the weekend, with up to 1.6in (40mm) of rain predicted to fall in some areas, with more thunderstorms across the UK also predicted.
But in a long-range forecast, the Met Office predicted there could be a “long spell of dry and sunny weather” around the end of August.
“There are signs that high pressure will increasingly dominate the weather across the British Isles,” the office said in a statement.
“Southern areas are most likely to see the driest and sunniest weather at first, perhaps with some lingering wet and potentially windy conditions affecting the north.
“However, longer spells of dry and sunny weather may develop across all parts.
“Temperatures are generally likely to be warmer than average.”