The Met Office have upgraded a weather warning in the region to Amber.
Forecasters say heavy rain is expected to bring some flooding and transport disruption to the area.
A band of rain will become slow moving and heavy across Wales, the West Midlands and into southwest England.
Many places will see 25-50 mm of rainfall, with totals of 70-90 mm expected over higher ground of Wales.
The unusual wind direction associated with the rainfall will mean that the peak rainfall totals are likely to occur in some areas that are usually well sheltered and drier during unsettled spells of weather.
The warning will be in force tomorrow from 12pm until 6am on Sunday.
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