Wet weather was moving in from the south west today to make it a soggy Bank Holiday for many.
The Met Office has issued a yellow weather warning in London, the east, south-east, and south-west of England, alerting the public to "thundery downpours" ahead.
Up to 25mm, or half a month of average rain, could fall in some areas, becoming increasingly heavy throughout the day before spreading to the north overnight.
MeteoGroup forecaster John Griffiths said today: "Patchy rain has been pulsing up from the south west. It's only bits and pieces for now, but it will get heavier later in the day."
That was likely to bring rain to the later stages of Notting Hill Carnival today, with more forecast tomorrow.
Mr Griffiths said: "There is expected to be heavy rain across much of England and Wales tomorrow, before conditions turn drier and cooler on Tuesday and for the rest of the week."
The Met Office said: "Thundery showers or areas of heavy rain are likely to affect some southern and eastern parts of England. Lightning may be an additional hazard.
"The public should be aware of the risk of localised impacts from heavy rain and flooding, which may affect travel and some outdoor events."