The Met Office issued a yellow weather warning for Friday, also covering the north of England and Northern Ireland. People have been told to expect slow-moving, thundery downpours which may lead to localised surface water.
A warning on the Met Office website says: "There is a small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater.
"Spray and sudden flooding could lead to difficult driving conditions and some road closures.
"Where flooding or lightning strikes occur, there is a chance of delays and some cancellations to train and bus services."
Heavy showers are expected across much of the UK on Friday.
The Met Office says rainfall totals will vary considerably and not all locations will be affected by the heaviest showers.
However, where the showers do occur there is potential for 20-30mm of rain in a short space of time and during the course of the day there is a chance that some places could see as much as 80-100mm build up.
The weather warning is in force from 10am on Friday until midnight.