The Met Office has issued a yellow weather warning for rain this weekend.
Another heavy spell of rain is set to hit parts of Brecon and Radnorshire tomorrow evening (Friday) and throughout Saturday.
The warning is in place between 9pm on Friday and runs until 3pm on Saturday.
Ystradgynlais and the entire Swansea Valley is included in the warning area, which snakes across the south-west of the constituency.
Llandovery in Carmarthenshire is set to be affected by the band of heavy rain, which may come as far east along the A40 as Sennybridge.
A spokesperson for the Met Office said: "Another area of rain will cross the UK starting from Friday evening, before it clears to the east during Saturday. Some of that rain, especially in southwestern parts of the UK, is likely to be heavy at times, and follows many weeks of above-average rainfall in this area.
"The associated weather system should clear to the east during Saturday afternoon, with more showery conditions following. 10 to 15mm is expected widely in the warning area, with a few places near southern coasts and over high ground seeing 20 to 30mm, with a chance that the southern slopes of Dartmoor and the hills of southwest Wales could see 40 to 50mm."
The forecaster has warned that spray and flooding could lead to difficult driving conditions and some road closures.
They have also warned of possible delays or cancellations to train and bus services, and potential flooding of a few homes and businesses.