After nearly four months of unusually warm conditions, including a record-breaking summer marked by five heatwaves, Britain could be about to experience its final spell of high temperatures this year.
Temperatures of 20C or above have been recorded somewhere in the country every day since June 11, an extraordinary run that is now expected to come to an end.
The Met Office says the week will begin with “warm” conditions before a colder pattern spreads across the whole of Britain.
Once early fog clears, widespread sunshine is forecast on Monday. Temperatures could climb into the low 20s across England and parts of Wales, with the south potentially reaching 23C (73F).
London could see temperatures of 21C (70F) on Tuesday. From Wednesday, however, daytime highs are expected to drop into the mid-teens Celsius, bringing conditions more typical of the season.
The shift in weather will follow a band of rain moving southwards from Tuesday into Wednesday.
Forecasters at the Met Office warn that the rain may become “potentially heavy for a time” across the southeast.
Brighter and drier conditions should return to most areas on Thursday, although the day will feel noticeably cooler.
A red deer stag stands in the sunrise during the annual rut at Richmond Park in London on October 2
Looking ahead to next weekend, forecasters expect changeable conditions as Atlantic weather systems bring spells of rain and showers to much of the country.
The cooler spell follows Britain’s fourth-warmest September since records began in 1884, according to provisional Met Office data.
Temperatures remained exceptionally high right through the final days of the month, reaching 28.1C (82.5F) at Kew Gardens in west London last Tuesday.
September’s average temperature was 14.6C, while rainfall totals were close to normal following a prolonged dry summer that was the hottest on record.
The impact of the summer heatwaves is also being felt by cider producers, who expect their poorest harvest since records began in 1984.
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Growers say the lack of rain placed apple trees under severe stress, damaging the crop.
At Burrow Hill Cider in Kingsbury Episcopi, Somerset, cider has been made for more than 300 years across 200 acres of orchards. This year, its harvest is around 50 per cent lower than last year’s.
The company said the “extremely long and hot summer” combined with limited rainfall caused the apples to ripen too early, remain smaller than normal and fall from the drought-stressed trees.
The hot, dry conditions could also create a striking but less predictable autumn, with the National Trust warning that some plants may flower outside their usual season.
There are already signs of a “false autumn”, in which drought-stressed leaves turn brown and fall prematurely. However, the National Trust says the potential for vivid autumn colour remains, especially if the coming weeks bring cooler, settled weather.
Strong sunshine should intensify the colour of foliage that has survived, although the overall display is expected to be more varied than usual.
But it is likely to be more varied than usual, the charity said.
Some plants have responded to recent rain with fresh growth or a second flowering out of season – meaning there could be spots where maples are in autumn colour alongside rhododendrons in bloom.
Luke Barley, senior national specialist in trees and woodland at the National Trust, said: ‘Autumn colour always depends on a combination of factors, but after such an extraordinary summer the usual signals are much harder to read.’
Trees may be more vulnerable than usual to high winds, the trust fears, as they may have to wet, stormier weather brought by the current super–strength El Nino whilst holding onto their leaves amid milder conditions.
The arrival of autumn also looks set to vary significantly from place to place, too, the National Trust said.
Gardeners at Cotohele in Cornwall are expecting it three to four weeks later than usual, as its North American ash – one of the first trees to turn, sometimes as early as August – only began showing hints of its pink–purple colour in the third week of September.
But one of the key signs of autumn – the conker – may be in short supply as drought has led to a less abundant, noticeably smaller, crop at its estates, the trust said.