The “persistent” rain on Saturday and Sunday is likely to cause disruption to travel with “lots of spray on the roads”, the national weather service said.
Alex Burkill, a Met Office meteorologist, said areas such as Devon and Cornwall could see coastal gales of up to 50 mph, with between 30mm and 40mm of rain expected to fall in areas with warnings in place.
"We have got a deep area of low pressure that will bring heavy and persistent rain, and strong winds too,” he said.
"In terms of rainfall totals, the greatest amounts could be up to 70mm. That will be over the hills and mountains," he added. "Away from there, some places could see 30mm to 40mm in a short space of time."
His fellow Met Office meteorologist, Becky Mitchell, added that the wet weather is expected to be widespread as “most places this weekend are likely to see some rain”.
Cities including Leeds, Manchester, Sheffield, Liverpool, Bangor, Swansea and Cardiff are covered by the weather warnings.
Mr Burkill said that large waves and high spring tides could also increase the risk of "coastal impact" in southwest England.
The Met Office said there will be sunny spells and showers across England and Wales on Saturday morning, before the worst weather arrives later in the evening.
The weather warning has already led to the cancellation of the inaugural Regatta London race, which was due to take place on the River Thames on Sunday.
Organisers said they were unable to safely run the event due to "stormy weather" affecting the river's water quality.
Going into next week, the rain is expected to ease but temperatures will drop by the middle of the week, with some parts of Scotland seeing single figure temperatures.
Agencies contributed to this report
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