Heavy downpours have started to lash parts of the UK on a day where almost a month's worth of rain is forecast to fall in some areas.
The Environment Agency has warned that flooding is possible in several places across England and Wales.
A severe yellow weather warning for rain has been issued by the Met Office which states that rail and road travel is likely to be affected by the downpours.
Up to 80mm of rain could hit some areas, according to Met Office spokeswoman Jo McLellan.
Singer Liam Payne was forced to cancel an outdoor charity concert in west London because of the wet weather and Bookmaker Coral said it has suspended betting on this month being the wettest on record.
Wales, as well as the north-west and south-west of England, are expected to be the worst-hit areas.
The Environment Agency has warned that areas near to the River Trent in Derbyshire could flood, as well as two locations in the Lake District.
Natural Resources Wales has issued a flood alert for some low-lying areas in Snowdonia.
The heaviest rainfall of the day at 11am has been in Killowen in Nothern Ireland, where 29.2mm of rain fell over a 12-hour period.
In St Bees Head, Cumbria, 16.8mm fell over the same period.
The Met Office warning runs until 10pm on Friday. The UK-wide average rainfall for the whole of August is 89.5mm.
The heavy rain is "clearing eastwards as the evening goes on" and Saturday is expected to be clearer, Ms McLellan added.
The Met Office said Londoners can expect to wake up to a bright morning on Saturday. The city should remain 22C throughout the day.
Clouds will start rolling in on Saturday night and the capital could see some rain coming across the city, which could fall until the early hours of the morning.
But by 6am the rain should clear and Sunday morning will again be bright and clear.
The sun will stick around for most of the day and temperatures will sit around 21 degrees, but there's a good chance of scattered showers later on Sunday afternoon - some of which could be on the heavy side.
