Flash floods could hit parts of the country as heavy showers follow the hottest day of the year so far, the Environment Agency and Met Office have warned.
The EA and Met Office warned communities in parts of southern, central and eastern England that they were at risk of flash flooding.
Heavy and thundery showers are expected to develop through Monday afternoon and into the evening which could result in localised flooding, the agencies said.
While the risk of flooding from rivers remains low, surface water flooding could occur as between 25mm and 50mm (1-2in) of rain may fall in some places.
An Environment Agency spokesman said: "Environment Agency staff are on 24-hour alert and teams are monitoring river levels as the band of rain moves across the country.
"The public are encouraged to tune in to local media for weather forecasts for their area and to keep an eye out for signs of surface water flooding."
The threat of heavy rain comes after temperatures soared in a heatwave that saw the mercury reach 32.8C in Gravesend, Kent, in the hottest day of the year so far.
A Met Office spokesman said the "sheer volume of rainfall falling in such a short space of time" in some areas could lead to surface water flooding in some places.
But the extremely dry spring, which has left some parts of east and central England officially in a state of drought, means that many rivers are at low levels and are unlikely to flood.
According to Meteo Group, the weather division of the Press Association, the south west has already seen wet weather and more showers and thunderstorms are expected in south east England and East Anglia.