Weather experts fear there is a chance that thunderstorms 'may cause some flooding and disruption' tonight (Sunday, May 15). The yellow warning has also been put in place for Monday (May 16).
A Met Office statement, just before 10am, read: "There is a small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater, lightning strikes or hail.
"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 slight chance that power cuts could occur and other services to some homes and businesses could be lost."
People are advised to stay safe when travelling in storms, rain and strong wind."
The Met Office said that, although the locations affected by thunderstorms 'remains uncertain', a 'few places' may experience a combination of heavy rain, frequent lightning and hail during Sunday night.
A spokesperson added: "Should thunderstorms develop, they are likely to move north from the south coast during Sunday evening into parts of south Wales, southern England and East Anglia overnight before gradually weakening during Monday morning.
"Whilst some places will remain dry, a few places may see 20 to 30 mm of rainfall in less than an hour, with frequent lightning and hail additional hazards."
This comes after Sussex residents enjoyed the warmest day of the year so far on Saturday.