The Met Office is warning of more heavy, thundery showers from Friday night into Saturday, with torrential downpours, frequent lightning, large hail and locally strong gusts possible.
A spokesman said: "Significant flooding is possible where these do occur from surface water as well as from small, fast responding watercourses. The frequent lightning, large hail and strong gusts could also be an additional hazard.
"The public should be aware of the risk of disruption from any of these elements."
The Met Office chief forecaster said; "The wild weather follows the build-up of very warm and humid air at the end of this week. The large amounts of energy available in the atmosphere coupled with high moisture content can lead to torrential downpours along with frequent lightning activity, large hail and locally strong gusts.
"In this situation many elements need to come together at the same time to form these thunderstorms and so there remains large uncertainty in their development. Indeed, the risk has been extended further west for this update, with further updates in the coming days."
An amber severe weather warning for parts of the UK has been issued by the Met Office as intense thunderstorms are expected through Friday night and the weekend which could cause disruption.
The first pulse of storms is expected to come through late on Friday and into the early hours of Saturday, as an area of possibly intense thunderstorms move north from the continent.
These are likely to extend up through parts of England and Wales, potentially moving into parts of Scotland by the afternoon.
Thunderstorms may also generate over the UK as temperatures rise through Saturday afternoon, before another pulse of storms is likely to move up from the continent later on.
Paul Gundersen, chief meteorologist for the Met Office, said: "We have storms affecting parts of the UK from three separate sources, each having the potential to affect slightly different areas at different times of the day.
"This means a large area is at potential risk from these storms, as identified by the amber warning, but not everywhere will see them - some spots could see a relatively fine day.
"This alert identifies the area of risk and where the thunderstorms do form we could see localised flooding, as well as the risks that go with lightning and hail. We'd advise people to stay up to date with our latest forecasts and warnings as the situation progresses."