The Met Office has issued a series of weather warnings, with heavy downpours, thunderstorms, lightning and even possibly hail in prospect.
The official forecaster’s warnings cover a period ending on Monday morning (28 May) although the warm bank holiday weather could also be washed with a few light showers.
And then the heavy rain is due to return on Tuesday, with almost half an inch – or 10mm to 12mm – possible during the daytime.
The Met Office said: “Heavy showers and thunderstorms will affect parts of southern Britain.
“There is a small chance that homes and business could be flooded quickly, with damage to some buildings from floodwater, lightning strikes, hail or strong winds.
“There is a small chance of fast-flowing or deep floodwater causing danger to life.
“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 communities become cut off by flooded roads.
“There is a slight chance that power cuts could occur and some other services to some homes and businesses could be lost.”
The forecast described very warm and humid conditions leading to thunderstorms, adding: “While many will miss the worst of the heavy rain, the thunderstorms that develop will produce torrential rain and hail and therefore some places could see up to 30mm falling in an hour.
“Thunderstorms will continue to develop across the southern half of the UK throughout Sunday, with some of these persisting into Monday morning.
“While many areas will see small amounts of rain, a few locations may see some very large totals, with 30mm possible within an hour and perhaps up to 80mm in three hours.
“Along with this, hail and thunder are likely – as well as some locally strong gusts.”