The Met Office has issued a “danger to life” warning as gale-force winds and 70mm of rain are forecast to hit Britain this weekend.
Warmer conditions on Friday morning will give way to heavy rain in the afternoon, which will slowly move northeast.
“There will be rain across many areas,” said Grahame Madge, a Met Office spokesman.
“And gales will be developing across the English channel.”
Low cloud, mist and hill fog will also develop on Friday, though there will be occasional moments of sunshine in the south.
By the evening, conditions will drastically decline, with heavier rain and blustery showers expected across the country.
Severe gales are also likely to develop in the southwest.
The winds will grow stronger on Saturday, with 60mph winds expected to arrive inland and 70mph gusts likely to hit more exposed areas, such as hills and coastal regions.
Four yellow weather warnings have been issued across the UK for Saturday.
A warning for wind is in place across the southeast and southwest from 4am to 4pm on Saturday.
“The strongest gusts [are] most likely across coastal southwest England where isolated gusts of up to 80mph are possible in very exposed locations during the morning,” the Met Office said.
“There is a small chance of injuries and danger to life from flying debris, more likely across southwest England.”
There is also a possibility that buildings could be damaged and that power cuts could occur.
“The strongest winds will probably be around 70mph and along the channel coast and areas like the Isle of Wight,” Mr Madge said.
A second warning for heavy rain is in place for the southwest from 6am to midnight on Saturday.
“We’re looking at 60mm to 70mm worth of rain in some isolated areas, and 30mm to 40mm quite widely. As always ... there is a risk of localised flooding,” Mr Madge said.
The Met Office has said the heavy rain could lead to “some flooding and travel disruption” in southwest England.
The Environment Agency has issued four flood warnings and 19 flood alerts across England.
Heavy rain is also expected to fall over northern Scotland, particularly over hills. Two warnings for rain have been issued for the country.
Both are in place from 6am on Saturday to 12pm on Sunday and forecasters fear parts of the region will be flooded.
“Flooding of a few homes and businesses is likely,” the Met Office said.
Significant delays to road, rail, air and ferry services are also likely across the UK.
Despite the series of warnings, temperatures on Saturday will remain mild.
“We’re looking at daytime highs of 13C for Southampton [and] 14C for the southeast and London,” said Mr Madge.
“Manchester will see double figures too, probably around 11C. Everywhere in England and, to be honest, even in Scotland will have a pretty mild day, though a wet and windy one.”
Sunday will begin with significant amounts of cloud and rain across the UK. Rain is expected to be heaviest in Scotland, Wales and southwest England.
The unsettled weather will continue into early next week, with rain and strong winds eventually subsiding before drier and colder conditions arrive in the southeast.
But signs of colder weather remain and the first wintry precipitation of the season is expected to fall on Scottish mountains, such as the Cairngorms over the weekend.
“The rain will be much more patchy on Sunday,” Mr Madge said.
“But there will be some more wind and rain on Monday.”
The meteorologist said unsettled conditions were likely to continue for the rest of the week, with temperatures likely to drop further as cooler air arrives.
“Nothing too drastic,” he added. “There will be a bit of frost, a bit of fog.
“It will be an unsettled week but we do see better periods existing within that.”
Additional reporting by agencies
