The Met Office has issued a severe weather warning for Friday, with the hottest day of the year expected to develop into an evening of thunder, lightning and even hailstones.
London and the south east will get the brunt of the “severe thunderstorms”, which are expected to begin on Friday and continue into the weekend.
It will come on the back of “very humid air” which arrived late Thursday and continued over to Friday morning.
Thunderstorms were forecast to begin as early as Thursday afternoon but were “more likely, and potentially more severe” on Friday afternoon.
Between 20 and 30 mm is estimated to fall within one hour. This is expected to continue overnight into Saturday, when 25-30mm is expected to fall “with the potential for some very high short-period totals”.
The Met Office, which has issued a yellow alert, warned of “very localised significant disruption, mainly from surface water flooding” as a result of the storms.
“Given the complexity of the developments leading up to this event, ideas on areas at greatest risk of heavy rainfall and severe thunderstorms may well change, and this warning will be updated accordingly,” it added.