The Met Office has issued a severe weather warning for heavy rain and possible flooding in parts of Britain including the east of England, London and the southeast, Northern Ireland, southwest Scotland, the Lothian Borders and Strathclyde.
For Saturday, Met Office forecasters say: "An active frontal system will become slow-moving for a while overnight across southeastern parts of England. Some bands of quite intense rainfall seem likely to develop for a time, with the risk of thunder. Many locations seem likely to see 20mm of rain, while a few places receive more than 30mm within six hours."
They add: "Outbreaks of rain will turn heavier and more persistent during Saturday night and the early hours of Sunday, clearing during the morning. The public should be aware of the risk of minor surface water flooding, perhaps exacerbated by leaves blocking drains."
Chief forecaster Leon Brown at The Weather Channel says: "After a wet Saturday, Sunday is expected to be a far better day with plenty of fine and quite sunny weather across England and Wales with light winds. Scattered showers near southern and western coasts are likely though, and especially over western Scotland."
Mr Brown said temperatures will be about average at 10 to 12C over the south and 7 to 9C in the north.
Monday morning will see a "misty and chilly start to next week, with a touch of frost too."
He adds: "There is likely to be more rain spreading to the southwest and Wales by midday, and some of it heavy. It will turn quite wet across much of the south by late afternoon on Monday."
For the rest of next week, The Weather Channel says there will be another band of rain moving northeast on Tuesday, before more showers for the middle of the week.
Mr Brown warned of "some heavy showers with thunder around coasts in the south."
The Independent reports that forecasters have warned of as many as ten days of miserable weather, with 50mph winds in some areas.
Just days ago, the National Audit Office warned that there was "insufficient" spending on flood protection in England.