Thursday is set to be sweltering with temperatures not falling below 18°C.
Scattered thunderstorms are set to move north tonight and early Wednesday which could lead to some power cuts and travel delays.
The hottest day the country has ever seen on record went down as 38.5°C, at Faversham in Kent back in August 2003.
The Met Office said there is a 40% chance the United Kingdom temperature record of 38.5C (101.3F), which was recorded in Faversham, Kent, in August 2003, will be exceeded.
There was a mixed bag weather-wise in Portsmouth yesterday, with thunder and lightning following blazing sun during the day..
Temperatures across the region are set to reach highs of 28C in parts today, as the weather turns hot and humid following heavy downpours overnight.
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Network Rail announced that speed restrictions would be in place in the south east from midday until 8pm amid fears that tracks could buckle in the heat if trains travel too fast.
A Met Office study into last year's record-breaking summer temperatures found they were about 30 times more likely as a result of climate change caused by human activities.
"Also tonight it's going to be very warm across central, eastern and south-eastern parts in particular as temperatures fall no lower than 23C to 24C in places, which could see further temperature records broken".
It is also the second hottest United Kingdom day on record, beating the 37.1C recorded in August 1990.
Overnight records in the United Kingdom could be broken by Wednesday this week.
It is also possible the all-time United Kingdom temperature record of 38.5C, set in Faversham, Kent, in August 2003, could be broken, and even the 40C threshold could be reached.
Heatwaves are extreme weather events, but research shows that with climate change they are likely to become more frequent.