Torrential downpours could bring a soggy start to summer, as early figures suggest this spring has been one of the warmest on record.
Despite the first day of June being bright and warm for most, there are no heatwaves on the immediate horizon, the Met Office said.
Muggy conditions overnight and potential thunderstorms in the South East on Friday are expected to give way to milder conditions over the weekend.
A yellow weather warning is in place for parts of the South East and East of England from 1pm on Friday, including East Anglia, London, north Kent, East Sussex and Surrey.
Warm, humid air coming up from France will bring the threat of thunderstorms and torrential downpours which have the potential for 25mm-30mm of rainfall in an hour.
Most places might miss the worst but there could be some localised surface water flooding "due to the intensity of the potential rainfall", forecaster Oli Claydon said.
Difficult driving conditions may also arise.
The South East will see the highest temperatures, with peaks of 28C (82.4F) possible.
But those hoping for a repeat of last weekend's scorcher are likely to be disappointed, with the mercury set to dip from Saturday.
Mr Claydon said: "In terms of the very mild conditions we saw towards the end of last week, we're unlikely to see a return to them, certainly for the next few days.
"By Saturday we are starting to see a reduction in those temperatures, temperatures feeling a touch cooler - probably more into the low 20s and the majority of the UK being in the teens."
The fresher conditions follow a spring which is likely to become one of the UK's hottest on record.
Early figures show the average temperature for the UK at 9C (48.2F) - above normal by 1.3C, and not far off the hottest spring recorded in 2011, when average temperatures were 9.15C (48.47F)
Northern Ireland is likely to have surpassed temperatures from spring 1945 - the current record - when the average was 9.13C (48.43F).