Thermometers will hit 20C in parts of the country next week with highs in the mid-teens expected nationwide. A huge low-pressure system wedged to the west of the UK over the weekend will funnel warm air in from the south.
Thermometers will stay around four degrees higher than the October maximum average of 13C, according to the Met Office.
Meteorologist Alex Deakin said: “Through the middle of next week there is a very strong signal that low pressure will dominate our weather.
“There is a strong signal for southerly winds particularly through the middle of next week to dominate, suggesting that we will keep low pressure to the west and high pressure to the east with that low pressure bringing southerly winds and keeping the temperatures high.
“The signal is also for temperatures being at least 4C above average through next week.”
However, it will not be all sunshine and blue skies as the low steers steer bands of rain into the country.
Western Britain is in the firing line for the heaviest and most persistent downpours while the east stays largely dry.
Warmer than average days, especially where the sun is strongest, will bring steamy nights, Mr Deakin added.
He said: “We are going to see some really quite warm nights through next week.
“We are likely to see some showers, and western areas are more likely to see the heaviest rain.
“It is going to remain particularly mild, with bands of showers moving more from west to east, and often at times it will be windy.”
As warm breezes sweep Britain, experts say the next fortnight holds no hint of anything wintry.
Britons will be wearing T-shirts through the rest of the month and possibly into November, they promise.
Jim Dale, meteorologist for British Weather Services, said: “This is certainly not what we expect in terms of temperatures for this time of year.
“There are no signs of winds coming from the north or northwest which we would expect to see at this time of year.
“With low pressure dominating, it is a southerly airflow, and we expect this to continue through the rest of the month.
“There is no cold in the forecast, no frosts and no ice. The next fortnight is going to be all about mild.”
Rain in parts of the country will be swept in on a plume of warmth from the Bay of Biscay, he added.
He said: “Showery rain will come in from France and the Bay of Biscay, and that trait looks like continuing through the next week at least.
“But otherwise, temperatures will be in the mid-to-high teens in this sub-tropical air from France and Spain.
“It is going to be T-shirt weather for some thorough the end of October.”
Warm air will be dragged up under the steam of the jet stream as it wraps around a giant low-pressure system.
Heavy rain will top up reservoirs and water supplies depleted after summer but also threaten floods in parts.
Weathertrending meteorologist John Hammond said: “Waves of wet weather will periodically sweep up across the country through next week.
“This will be welcome where long-term water reserves remain very low.
“But some western areas will be particularly prone to surface-water flooding during these rainy bouts.”
However, the chances of Britain seeing any hints of winter in the next 10 are close to nil, he added.
He said: “There’s absolutely no sign of cold in the near future.
“As the jet string digs down on one side of a huge trough in mid-Atlantic, it’s inevitable that in response, closer to home, air will be pumped up from the subtropics.”