“This system has the potential to cause disruption, and severe weather warnings are likely to be issued over the weekend as details become clearer,” he added.
Outbreaks of rain will become persistent and heavy, the Met Office said, with up to 40mm (1.6in) of rainfall in some areas and 60-80mm of rain over Dartmoor and high ground in south Wales, which could amount to more than half the average monthly rainfall in December.
Spray and flooding on the roads could cause difficult driving conditions, the forecaster said, with a chance of cancellations to train and bus services.
There is a small chance of some communities being cut off by flooded roads, as well as of homes and businesses being damaged by rising water.
The Met Office warning also highlights the possibility of fast flowing water causing danger to life, with some areas also facing the potential of power cuts.
