The warmest October day for five years was recorded in the south of England on Sunday, as some parts of Scotland saw one month’s rain in 24 hours.
Temperatures reached 25.8C in Kew Gardens, Surrey, and the average for October in London is usually 17C, the Met Office said.
But northern parts of Scotland have been much colder, with 9.4C recorded in Lerwick, where the average early October temperature is 10C or 11C.
Much of Scotland has also been devastated by flooding, with some regions experiencing one month’s rain in 24 hours over the weekend.
Landslides blocked some roads in the west of Scotland on Saturday, with 10 drivers being rescued by helicopter after becoming trapped on the A83 near Inverary in Argyll and Bute.
The Met Office posted on X, formerly known as Twitter, saying: “It’s been another unseasonably warm day for most – in fact the warmest October day for 5 years.
“But northern parts of Scotland have been much colder.”
The Met Office added that average early October maximum temperatures are: London 17C; Cardiff 16C; Derrylin 13C; Auchincruive 13C.
Met Office meteorologist Simon Partridge said Monday could also be an unseasonably warm day in the south of England, with temperatures of 24-25C forecast, potentially 26C.
But on Tuesday the rain will return for western Scotland, with a yellow warning in place and the potential of between 40mm and 50mm of rain.
And it is likely similar areas will be affected to those which were hit by flooding over the weekend.
“The amount of rain could bring them back to square one again,” Mr Partridge said.
In southern England on Tuesday, the temperature is likely to be 22-23C, but the rain will move further south throughout the day until it covers Wales and the Midlands.
Outbursts of heavy rain could be seen on Wednesday, particularly over Wales and the Midlands, the forecaster added.
Temperatures also will be gradually dropping over the week, and by Thursday most of the country will be seeing average temperatures for October, but the very south could see 19-20C.