A yellow weather warning for rain over South Wales and parts of Mid Wales is currently in force.
The heavy and persistent rain could have some flooding impacts, although some areas will miss the worst of the downpour.
Spray and sudden flooding could lead to difficult driving conditions and possible road closures. Trains and bus services could be delayed or cancelled due to the weather.
A spokesperson for the Met Office has said: “Where heavy downpours occur, 20-40 mm are possible within an hour or two. Over a longer period a few places could see more than 50-60 mm, possibly even as much as 80 to 100 mm if repeated batches of heavy rain affect the same locations - this perhaps more likely during the second half of Thursday.”