Had something similar here in Ayrshire a couple of weeks back, a thunder storm that just sat overhead for about 5 or 6 hours, nice bit of flash flooding too. Came without warning too, didn’t feel like a thundery day, I was out watering my pot plants a few minutes before it started, worrying they were going to dry out, half an hour later I was trying to stop them floating away
Got caught out on the road bike in that storm, was lovely when I left the house, came up over Carrick hill from the east, and could see it coming in from the north. Tried to race it home, got less than 2 miles, no jacket, water running out my shoes…. 😀
It is dry here in Ayrshire at the mo, but looks very threatening.