Forecasters have issued a yellow "be aware" warning for Wales as rain is set to hit most of the country.
The Met Office said showers moving in from the Irish Sea would turn heavy and thundery on Tuesday, especially in the afternoon.
Some areas could see localised flooding on roads and drivers should expect longer journey times.
Between 15mm and 20mm of rain could fall within one hour, with up to 30mm in three hours.
The warning is in place until 23:55 BST on Tuesday.