Heavy downpours and strong winds are due to pelt parts of the UK, according to two Met Office yellow weather warnings.
The alerts cover the entire south coast of England, as well as most of Wales, the Midlands and parts of the North on Wednesday.
A wind warning covers coastal southern areas of England from 4am to 6pm, while thunderstorms and heavy showers could batter cities including Nottingham, Oxford and areas of London, according to the second warning, which runs from 9am until 7pm.
The gusts on the south coast could reach speeds of up to 60mph in the most exposed areas.
The “unseasonably windy” conditions are expected to disrupt travel by delaying trains and ferries, as well as affecting roads, with some flooding predicted due to the slow-moving storms.
High-sided vehicles will be at risk on the roads and some communities could be left without power.
It will be particularly hazardous on seafronts due to spray and large waves.
UK weather: Will it stop being cold, wet and windy soon? Here’s what forecasters are expecting
Sea temperature in Florida reaches 38C – potentially a world record
Scientists warn deadly extreme heat ‘rapidly on the rise’ – and predict how often heatwaves will now occur
The latest Sky News weather forecast
Further north, the second weather warning cautions the public about the dangers of lightning damage to some buildings.
There may also be delays on the roads and on the railways, with a risk of short term power cuts in some areas, too.
Met Office chief meteorologist, Dan Suri, said the tempestuous weather is being caused by an “unseasonably deep area of low pressure” due to cross from Ireland into Wales and England during the day on Wednesday.
While heavy rain will affect large parts of the UK tonight, the heaviest downpours will fall tomorrow, he added.
A mix of sunshine and showers are forecast for Thursday and Friday, culminating in a wet weekend.
There are currently no further warnings for the rest of the week.
No sign of summer’s return
Forecasters have also revealed no signs that prolonged sunshine is on the way for the UK.
Much of the country will see cooler weather in the coming days, as Sky News weather producer Chris England said the weather would remain “unsettled”.
He added: “There’ll be some drier days of course, but there’s no real indication of any prolonged dry and sunny spells.”
The cooler UK conditions come as much of southern Europe has endured a heatwave which will still see temperatures reach 36C (96.8F) in Spain and Greece this week.
Read more from Sky News:
Dartford Crossing drivers frustrated after website crash
Why Venice could feature on a danger list of heritage sites
Be the first to get Breaking News
Install the Sky News app for free
Mr England said: “As for the Mediterranean, it’s mostly hot and dry, but most places have temperatures around the average for the time of year.”
July became the world’s hottest ever month on record, with the extreme heat also hitting parts of the US, Canada, France and Italy.
