Surely there's some mistake here. Have a look at this snippet from MetCheck's short term forecast for today in OX3, Oxford. The earlier period from 10:00 to 13:00 has just passed so has dropped off the screen, but it was showing 1.8mm of rain in that period. It's been tipping buckets all morning. But the forecast seems to be saying that in the mid-evening this evening it will be 10.8mm (it was 11.7 earlier) in two hours as against 1.8mm in three hours this morning.

My flat is prone to a bit of rainwater flooding as the door is in a bit of a dip halfway down a hill peppered with springs and so the run off is huge. SO it will be interesting to see what this order of magnitude increase in the rain from this morning to this evening will be like!