That could cause flash flooding and rising river levels.
The warning says: "The rain will be locally heavy with up to 30mm in places, but hills exposed to the southwest could see 40mm of rain. The period of rain is expected to last for six-nine hours. The Environment Agency is warning that everywhere in England and Wales is currently saturated and there is the risk that any further heavy rainfall will run off the ground and go straight into the rivers. As a result, we could see the levels in watercourses responding very quickly."
Sky News weather forecaster Lucy Verasamy said it was unclear which areas would be hit hardest. "There is some uncertainty as to the rain's northerly extent but vulnerable areas are at risk," she said."So it is worth checking the Sky News weather forecast over the weekend to see how things develop."