Most of the country is experiencing or expecting heavy rain as the miserable spell of damp weather continues.
Another big day for the umbrella
Torrential downpours are forecast to persist until at least midweek, as unsettled conditions continue.
Central, northern and eastern parts of England started the day cloudy and wet, with heavy rain. Sunshine, showers and storms were due later on.
Scotland is set to be wet all day and heavy storms are predicted for western England, Wales and Northern Ireland.
Forecasters expect western parts of Scotland to be worst hit.
On Tuesday sunny spells and heavy showers were forecast, followed by torrential rain on Wednesday, with hail and thunder.
The wet weather is moving in from the Atlantic, according to a Met Office spokesman.
He said: "There will be heavy rain and thunder, as well as a risk of flash flooding, in many parts of the country until Thursday, when there are likely to be light showers.
"Friday will see heavy and prolonged showers, especially in the west of the country."
He added: "The end of the wet weather is not in sight yet - by the end of the month most parts of the country will have had above average rainfall.
"There is a slight chance of sunshine during September."
The further rain came as the clean-up operation in the south west, including flood-hit Boscastle in north Cornwall, continued.
The historic village suffered severe damage during flash flooding a week ago when a wall of water rushed along the main streets, sweeping cars and trees before it and leaving buildings structurally unsafe.