A Met Office spokesperson said: "There is a chance of thunderstorms popping up across large parts of the United Kingdom today as temperature rise, but many places will avoid these and enjoy a dry day".
The weather outlet warned there will be torrential rain, lightning, hail and poor visibility on the roads during the thunderstorms.
Downpours could see totals of 20-30 mm of rainfall in an hour, with some locations potentially receiving 40-60 mm in three hours.
The impacts from heavy, intense rainfall have been felt in many places, including Fife in Scotland, where an Amber warning was in place and a major incident was declared.
The formal forecast for tonight reads, "Scattered heavy thundery showers during the evening will continue overnight".
Homes and businesses across central and western Wales have also been flooded.
Neil Davies, Flood Duty Manager at the Environment Agency, said: "Isolated thunderstorms could bring sudden surface water and river flooding to parts of England today, which may lead to flooded properties and severe travel disruption in some areas".
However, this morning's update provides more information about the small risk of flash floods.
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People have been enjoying the hot weather in Barry Island.
Some areas will experience temperatures over 20C throughout the night.
Following the ongoing heatwave, Public Health England issued a heat health alert for parts of England into next week.
Under its yellow warning, the Met Office is predicting storms in particular for the north-west, north Wales and the West Midlands for Wednesday and Thursday.
Across the rest of the week Tuesday will be another hot day according to the Met Office, with many areas remaining dry throughout.
Met Office forecaster Craig Snell said: "For England and Wales over the next four days, there is a risk of some very severe weather in places but it is not going to be everywhere".
Heatwaves are extreme weather events, but research shows that climate change is making these events more likely.