A yellow weather warning has been issued over Brecon and South Wales by the Met Office for Thursday, December 7 from midnight until 3pm.
The warning for heavy rain is likely to cause some flooding and disruptions to travel.
Bus and trains services in the area are likely to be affected by the weather with spray and flooding on the roads making journey times longer.
The Brecon Beacons is likely to see 60-80mm of rainfall, with other areas of the region expecting 30-40mm.
The rain is expected to be persistent over Wednesday night and become heavier throughout Thursday.
(Met Office)
The Met Office's warning impact matrix shows that heavy rain is likely to occur with a low impact.
Follow the link below to see tips of how to stay safe in heavy rain: