The warm weather in London is showing signs of breaking up - but it is hoped that conditions will be dry for the opening ceremony of the Olympics on Friday evening.
Overall there are signs of a return to the rainy weather that has characterised the British summer so far.
After several days of hot dry weather, there are expected to be some showers in the London area on Saturday, said Matt Dobson, senior forecaster with MeteoGroup, the weather division of the Press Association.
"It will remain humid, and some of the showers may be thundery," he said.
"However by the time of the opening ceremony, the showers should be moving away to Essex and Kent, with drier weather coming in from the west."
Temperatures during the day are expected to peak at 26C (79F), a little cooler than the 29C (84F) seen on Friday at Dorney Lake, Eton, and the 31.4 (89F) on Saturday at the Olympic Park in Stratford, which was the hottest day of the year so far.
"The weekend will be cooler than we've seen recently, with some sunshine on Saturday, but showers on Sunday, and then next week it's back to square one, with lots of rain around, all over the country. There will be drier interludes, but it will be like the weather we had become used to, looking ahead for a week to 10 days."
The reason for the poor weather returning is that the jet stream, which had moved away north, is heading south again.
Its presence unusually far south earlier in the summer brought the wettest period of April to June on record, heavy rain and widespread flooding.
Its move to the north brought a spell of more traditional summer weather, which is on the way out.
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