While drier conditions will continue into Monday for most places, Tuesday will see low pressure arriving from the south-west. This will bring showery conditions for parts of southern England and south Wales.
By Wednesday, downpours will become more widespread across England, Wales and Northern Ireland, while Scotland is likely to remain mostly dry.
There could be some heavy and thundery bursts.
From later on Wednesday until Friday, the threat of torrential downpours with hail and thunderstorms will increase.
The areas most at risk are southern England and Wales, where heavy rain falling on dry and hard ground may bring the risk of localised flooding.