The yellow warning is in place from 11am on Thursday until 8pm.
According to the Met Office heavy showers and thunderstorms on Thursday have the potential to bring surface water flooding in a few places, and disruption to travel.
A spokesperson said: "Following overnight rain and showers, more intense showers and thunderstorms are expected to break out fairly widely from late-morning, before easing during the evening.
"Whilst most areas will miss the most intense storms, torrential downpours are possible in a few places. Where these occur, there is potential for 20 to 30 mm of rain in less than an hour and up to 40 mm in 2 hours. This would have the potential to generate surface water flooding, especially if it falls over an urban area."
What to expect according to the Met Office
There is a small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater, lightning strikes, hail or strong winds
Where flooding or lightning strikes occur, there is a chance of delays and some cancellations to train and bus services
Spray and sudden flooding could lead to difficult driving conditions and some road closures
There is a small chance that some rural communities could temporarily become cut off by flooded roads