On 15 Sep, 20:11, Nick wrote:

Seems to have been much worse in the central south (I'm in
Southampton) than the southeast. Mostly light but seemed almost
torrential for a short while around 6.30pm. I have to admit I'm amazed
at how active this system, which just seemed to be a minor trough on
the south side of the high, has been.

Given the linear nature of the rainfall, I am beginning to suspect
some of my favourite - conditional symmetric instability - might be at
play. Basically the sort of instability you get at thunderstorms but
along frontal surfaces that organises rainfall in narrow, intense
bands - however the alignment of the jet and the local temperature
gradient suggests that it might not be the case.

Certainly I can't remember a day since working in the City where I've
seen such heavy rain throughout the day. Surprised Clerkenwell was
only showing 15mm as per Phil's email just now.

Richard