A yellow weather warning has been issued for thunderstorms, which could lead to flooding in parts of England and Wales.
The warning covers areas including Wales, the Midlands, west of England, London and the South East from 12:00 BST to 22:00 on Monday, the Met Office said.
Up to 50mm of rain could fall within a few hours, with a possibility of delays and some cancellations to train and bus services.
England has had its driest start to spring for 69 years, the Environment Agency said earlier this month.
Showers are forecast to drift in from the south in the early hours of Monday, the Met Office said.
Temperatures across the board are due to remain mild in the high teens or early 20s.
The Met Office said there was the “potential for minor localised issues” and flash flooding.
Sunshine and settled conditions will return across the UK for the rest of the week, with temperatures forecast to reach 23C in some parts.
Last week, the Environment Agency warned that water companies that more must be done to safeguard water supplies.
Many places have gone without any rain for weeks, including Preston in Lancashire and parts of Fife which have been dry since mid-April.
According to the UK Centre for Ecology and Hydrology’s three month Drought Index, large parts of the UK are in the ‘extremely dry’ category.
