Temperatures could hit the hottest of the year today - but torrential downpours and "intense" thunderstorms are also forecast to sweep across the country.
Despite blue skies greeting most of the UK, people in the South West and Wales are expected to wake up to torrential downpours as well as thunder and lightning.
The Met Office has warned of potential flooding, as 2cm to 3cm of rain is expected to fall in an hour in the south.
The fine and bright start for the rest of the country could see temperatures push as high as 26C or 27C (78.8F to 80.6F) in London. The hottest recorded day of the year so far was last Friday, June 5, when thermometers hit 26.7C (80.06F) in Frittenden in Kent.
But today's sunshine will be interrupted in the mid-afternoon in the south when "isolated and intense thunderstorms" will start, reaching the north by the evening.
A Met Office spokesman said: "We were already seeing thundery activity across the South West and as temperatures continue to rise it will lead to more. Friday night could be a lively one."
Following the severe thunderstorms will be a band of more widespread and heavy downpours on tonight and into tomorrow, when up to 5cm of rain is expected to fall.
A Met Office spokesman said: "During Saturday it should brighten up quite nicely.
"By Monday it will feel fresher, not as hot and humid as Friday. Temperatures will dip to the low 20s, but it will still feel quite pleasant and temperatures will still be higher than average for June, which is about 18C or 19C (64.4F to 66.2F) in the South East.
"We will be left with quite chilly nights but nice, sunny days."