Sky News weather presenter Jo Wheeler said: “Some areas may miss the showers, but where they occur, there’s likely to be hail, thunder, lightning, gusty winds and a temporary temperature drop.”
Almost 50mm of rain could fall in some places in just a couple of hours, she added.
While a dry spring means rain is needed in many areas, “the heavy nature of these showers [means] there is the potential for minor localised issues and flooding,” Met Office meteorologist Jonathan Vautrey said.
The Met Office said the rain could lead to difficult driving conditions and some road closures.
There is also a chance of power cuts and flooding, it added. People who live in areas at risk of flash flooding should consider preparing a flood plan and emergency kit, the Met Office warned.
The high pressure will rebuild from Tuesday, and dry conditions and sunshine will return across the country, Mr Vautrey added.