Heavy rain could cause "disruption and probable flooding" on Monday with an amber weather warning in place for south Wales.
The Met Office said heavy rain, external was expected over south Wales from late Sunday and throughout Monday, with 20-40mm (0.78-1.58in) expected across the wider region and 100-120mm (3.9-4.7in) in a few places on higher ground.
A yellow warning of rain, external is also in place for mid and north Wales on Monday, with the Afon Glaslyn in Beddgelert, Gwynedd, nearly broaching the garden wall of a house nearby.
The weather alerts come two weeks after danger to life flood warnings were issued and homes and businesses in Monmouth and elsewhere hit after rivers burst their banks.