Britons are expected to soak up the hottest weather of the year so far today - but forecasters are warning that the drifting ‘jet stream’ will bring cooler conditions next week.
The mercury may reach as high as 30C (86F) in London, with temperatures in the high 20s in other parts of the country.
That will beat the previous high of 29.3C (84.7F) set in Achnagart, in Scotland, on May 25.
But Sky's Isobel Lang said it would be cooler and breezier around the coasts, and temperatures would drop again toward the end of the week.
The risk of thunderstorms on Friday may put a dampener on the Olympics opening ceremony in east London.
Lang said Tuesday's 30C high would be several degrees short of the all-time July record of 36.5C (97.7F), which was recorded in Wisley, Surrey, in 2006.
"The heat will last all week across the south, although the risk of thunderstorms is set to increase during Friday threatening the opening ceremony," she said.
"During the first weekend of Olympic events it is going to feel much cooler with temperatures nearer 21C (69.8F) on Saturday with sunny spells and a northwesterly breeze.
"Sunday could be a little cooler still with the chance of a few showers.
"The jet stream has returned to its more 'usual' summer position to the northwest of the British Isles this week with high pressure bringing the sunshine and heat across the south.
"However, it does look as though it will meander southwards again during the coming week bringing cooler and more changeable conditions for the first week of the Games.
"Some drier, sunnier spells are still likely and it will be worth keeping an eye on the latest forecasts for those planning on watching the events."
The current hot spell comes after weeks of seemingly relentless rain in some parts of the UK.
The wettest April to June period on record led to widespread flooding, disruption and deaths.