Thermometers are expected to hit 20C in southern Britain ahead of the weekend, according to the Met Office. Meteorologist Aidan McGivern said: “The jet stream is coming out of North America and strengthening on the other side of the Atlantic.”
“Areas of low pressure will be picked up by the jet stream from a breeding zone for these areas of low pressure just to the southwest of the UK, and they will be pushed north over the next few days.
“Temperatures will be well above average for the time of year, 19C to 20C in the south, and a touch lower, 13C to 15C for Scotland Northern Ireland and northern England.
“It’s going to feel like autumn with spells of wet and windy weather, but it is not going to feel like October with those temperatures.”
As weather fronts plough into the UK this week, the country will be wedged into a warm sector of steamy air.
However, without wall-to-wall sunshine, Britons have been told not to expect a ‘classic Indian summer’.
Mr McGivern said: “Temperatures will be well above average both by day and by night.
“But it won’t be a classic Indian summer because at the same time we are going to see spells of wind and rain push up from the southwest to especially affect western parts of the UK.
“A developing low pressure is likely to push up from the south on Friday, and it is likely to bring further spells of wind and rain.
“In between a warm and a cold, front we have a warm sector, a very warm sector for the time of year, and that means we start off Friday with temperatures even higher than Thursday morning.”
Warm air swept in from the Continent will push temperatures around 5C higher than average for the time of year.
A ‘sub-tropical’ airflow will steer balmy breezes into Britain originating from near the Canary Islands.
Jim Dale, meteorologist for British Weather Services, said: “The air that is coming into Britain will be sub-tropical, and this is going to have come from Spain and Portugal, and from the Atlantic towards the Canary Islands.
“It is still touch and go whether it is going to be wet or mild for Halloween, there might be more in the way of rain to come at the end of the month.
“However, in the immediate forecast, there are no signs of anything colder on the horizon.”
Sea waters still warm after the extraordinary summer heatwaves will help to drive the mild weather, he added.
He said: “With the sea still warm, and with a lot of humidity it is going to be very mild for the foreseeable future.
“This will be accompanied by outbreaks of wetter weather, and this is the pattern we expect to see until the end of the month.”
The soggy outlook has prompted Bookmaker Ladbrokes to slash the odds on the wettest October on record.
Spokesman Alex Apati said: “We’re strapping ourselves in for record-breaking October rain over the next few days.”