An amber alert has been issued for parts of the UK which has been warned to prepare for thunderstorms and severe flooding, with a month's worth of rain due to fall in just an hour.
The Met Office has warned millions of people in Wales and the North West of England could be affected by the adverse conditions.
Flooding of homes and businesses is said to be "likely" and could happen quickly, with some buildings expected to be damaged by floodwater, lightning strikes, strong winds and hail.
Spray is likely to cause dangers to road users while people relying on public transport could also have issues with buses and trains expected to be cancelled or delayed.
The amber alert came into effect at 5.45pm and continues until 9pm this evening.
The Met Office's amber alert reads: "Very heavy showers and thunderstorms have developed along a line running from the Worcestershire towards northeast Wales and Merseyside.
"The most intense showers are expected to transfer northwards with time. As such some locations could see multiple showers and thunderstorms, resulting in 50-60 mm of precipitation in an hour or so (this represents around a month's worth of rain), and perhaps some isolated spots seeing more than 100 mm in a few hours.
"Lightning, hail, and perhaps towards the east of this area the odd strong gust of wind, will be additional hazards."
The announcement comes as the UK officially recorded the hottest day of the year so far as temperatures exceeded 32C.
The highest temperature of 2023 was recorded in Chertsey, Surrey, which reached 32.2C during the afternoon.
It is the first time since August 24, 2022, temperatures have gone above 30C in the UK, the Met Office said.
The whole country is experiencing a heatwave - and the warm weather is here to stay for the next few days, according to forecasts.
Met Office meteorologist Jonathan Vautrey said: "Temperatures will be notably above average for the time of year, climbing towards our first 30C of the year, so really feeling warm and some very strong UV levels as well.
"If you are suffering from some of the heat though, do head towards some eastern coastal areas because there is just a bit of a breeze pushing in from the sea."
Mr Vautrey also warned pollen levels are very high across England and Wales, as well as Northern Ireland and Scotland.
Regions and local authorities affected
North West England
Cheshire East
Cheshire West and Chester
Greater Manchester
Halton
Lancashire
Merseyside
Warrington
Wales
Denbighshire
Flintshire
Powys
Wrexham
West Midlands
Herefordshire
Shropshire
Staffordshire
Telford and Wrekin
Warwickshire
West Midlands Conurbation
Worcestershire