The persistent downpours could bring flooding and disruption to parts of the UK this weekend, as the Met Office issued weather warnings covering large areas of the country.
It comes after a low-pressure system named Storm Alex moved in from France and clipped the southern edge of Britain on Friday.
It brought heavy rain and strong winds, with the highest gust of 71mph recorded at Berry Head on the Devon coast.
The Met Office warns there is likely to be flooding and disrupted travel.
Many places will see 25-50mm of rainfall, with totals of 70-90mm expected over higher ground of Wales and south-west England.
Yellow rain warnings are also in place for the east of England, London and the South East plus much of Wales, western England and eastern Scotland where heavy rain is set to push in from the north west.
The rain is set to last throughout Saturday and into Sunday in these areas, the Met Office said.
Mr Dewhurst said “it is going to be raining and horrible all day” on Saturday, adding: “If you have to travel take extra time on your journey, the roads will be pretty treacherous at times with poor visibility due to the heavy rain.”
Drains could become blocked with debris as trees are now in full leaf and there is a heightened risk of flooding and very difficult driving conditions.
Met Office chief meteorologist Steve Ramsdale said now that the strong winds and rain linked with Storm Alex have cleared away, another low-pressure system has moved towards the UK from the east.
It will bring “further very heavy rain to many over the weekend as well as some strong winds,” he said.
Met Office deputy chief meteorologist Laura Ellam said Saturday will be “a very wet and cold day for many” and the weekend will see a “spell of challenging and disruptive weather”.
She said: “Conditions will improve for many on Sunday though it is still likely to remain wet and windy for some.”
She added: “In areas with amber warnings, such as Snowdonia, Exmoor and eastern Scotland, over 100mm of rain could fall over the weekend – this is likely to lead to significant impacts from flooding.”
Carol Holt, flood duty manager at the Environment Agency, added that “widespread and persistent rain is likely to lead to flooding” in some areas over the weekend.
She added: “We urge people to stay away from swollen rivers and not to drive though flood water – it is often deeper than it looks and just 30cm of flowing water is enough to float your car.”
RAC Breakdown spokesman Rod Dennis said that road conditions will be “miserable if not downright dangerous” for drivers this weekend.
He said they will need to be prepared for “an ugly mix” of surface spray, gusty winds and more than likely some disruption on the roads.