The Met Office has issued a yellow rain warning for London and the South East early this week.
From late tomorrow morning (Tuesday 8 August), showers are expected to develop across parts of the east and south east of England, the weather service said.
"Whilst many will miss the worst of the rain, the heaviest showers could bring 25 mm in an hour to some spots with 40 mm in 3 hours possible," the Met Office continued.
Meanwhile, a slow-moving weather system affecting southeastern parts of Britain "will give 20-40 mm of rain quite widely across the area, with perhaps as much as 60-80 mm in places through the whole day" on Wednesday.
In some places 20-30 mm could fall within 2 or 3 hours, but the Met Office added: "At this stage there remains uncertainty in the exact location of the largest rainfall totals."