Between 25-30mm of rain could fall in just one hour – equivalent to around half the average rainfall for England in the month of June (which is 62mm or 2.4 inches over the course of 10 days.)
The risk spot takes in the area encompassing London and the south east, the east of England and the east Midlands. Localised surface water flooding is possible, as are lightning and hail between the hours of 1pm and 11pm.
While sandbags might seem like an appealing idea during the lull before this storm, it’s worth bearing in mind that these short, sharp bursts of prolonged rainfall are likely to move across the country, meaning areas in the line of fire may not receive the full measure.
It will still feel warm and muggy however, thanks to a blast of very warm, humid air from France.
As a comparison, New Taipei City, in Taiwan, had 634.5mm of rain in 12 hours – which is more than London’s average annual rainfall.
After all that, be prepared for things to feel considerably more fresh by the weekend – come Saturday temperatures will be dropping to 22/23C. This time last week was the hottest day of the year so far, with a peak of 29.4C registered in Lossiemouth, north Scotland.
Another step down will occur on Sunday, with temperatures set to fall to the low teens, early 20s.