An area of heavy rain reaching southwest England late Wednesday afternoon spreads eastwards across southern England, reaching the far southeast of England by mid-evening.
Rain will last for around six hours in any location, finally clearing southeast England during the early hours of Thursday. Rain may be accompanied by coastal gales and, in a few places, thunder. 15 to 25 mm of rain is widely expected with 30 to 50 mm possible in a few places.
It has indeed already started (set to worsen around 7pm) and is set to continue for some hours into the morning.