The Met Office has issued a thunderstorm warning for England and Wales today, with up to two inches of rain expected in places.
Forecasters have predicted flooding as part of the alert, which is in force from 9.42am until 11pm this evening.
Downpours are already hammering the Isle of Wight and the torrential rain is expected to spread across Britain this afternoon.
South-east Wales and south-west, south and south-east England are all set to be affected.
The Met Office warning states: "Heavy showers already affecting the south and east of the Isle of Wight will become more widespread across the warning area through the afternoon, with some thunderstorms also developing.
"These may be quite slow-moving and last for an hour or two. Some torrential downpours are possible with a few places seeing 50 mm of rain or more within a few hours. Lightning and hail are also additional hazards."
Earlier today the Met Office said people should expect "some heavy, and perhaps thundery, showers" with rainfall breaking out across England and Wales.
In its long term forecast up to Friday meteorologists said: "Showers or longer spells of rain each day for most areas, these occasionally heavy and thundery, and accompanied by hail.
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"Winds mainly light throughout, with temperatures around normal."
With the fresh rain set to fall, flood warnings have now been issued for a couple of regions in England.
The Environment Agency currently has one flood warning, meaning flooding is expected and immediate action should be taken, for Buxted in East Sussex.
The miserable outlook comes after Storm Evert battered parts of the country last week, producing ferocious gusts of winds close to 70mph across Cornwall and the Isles of Scilly.
The storm pushed away east of England into the North Sea on Friday night, taking gale force winds with it.
Meanwhile, forecasters say Thursday could see a 400 mile-wide Atlantic torment with 60mph gusts on the way.
Met Office forecasters have said another storm risks being named after the washout that was Storm Evert.