UK basks in late September warmth before Atlantic fronts bring wind and rain

Britain is enjoying a final burst of unusually warm weather this week, but forecasters warn that a deep Atlantic low is about to bring a return of wind, heavy rain and gales to much of the country.

Helen Willetts, lead weather presenter at the BBC Weather Centre, said a vast area of low pressure sitting out in the Atlantic is set to draw warm winds from the south and south-east across the UK early in the week. For many, however, the warmth will be short-lived, with rain arriving not far behind.

Monday is expected to be notably chilly to begin with, despite the sunshine. Last week brought the autumn equinox, and with nights now longer than days, clear skies are allowing temperatures to fall further after dark. Some patches of fog are also possible, which could make Monday's commute a difficult one. Once any mist lifts, high pressure is expected to deliver a brighter day for most parts, with sunny spells and only a few scattered showers.

The odd spot of rain could reach south-east England during Monday afternoon and evening, though forecasters stress this is not guaranteed. Temperatures on Monday are expected to range from the mid to high teens, with some southern areas reaching 20C.

Tuesday is predicted to be the warmest day of the week, as a strengthening southerly wind drags milder air northward. Forecasters expect high teens in Scotland and Northern Ireland, and between 20C and 26C across England and Wales. After that, temperatures are expected to settle back closer to the September average.

The warm spell comes with a caveat for the west. Rain is forecast to move into Northern Ireland during Tuesday afternoon, then track slowly eastwards through the evening and night. The weather could become persistent and at times heavy, accompanied by strong winds and gales on exposed coasts and hills. Areas further east may hold on to drier, brighter conditions before the rain finally arrives on Wednesday, where it may hang around overnight.

Wednesday itself is forecast to bring sunny spells and scattered showers in the wake of the front, with the wind still noticeable in the west. By Thursday, high pressure is expected to build across the country, bringing calmer and drier conditions. By Friday, the north-west is set to become the focus for any further showers. Forecasters caution, as always, that these details may shift, and advise people to check the latest short-term outlook for their area.

The current warmth is unusual in the context of what has gone before it. Following the UK's hottest summer on record, September has proved to be another notably warm month for many people, helped by plenty of sunshine. But the month has also exposed a sharp divide across the country, with persistent Atlantic weather systems battering Scotland and other western areas while much of central, southern and eastern England remained largely dry.

Rainfall totals have consequently varied dramatically. Some drought-affected parts of England have seen very little, whereas parts of north-west Scotland have been exceptionally wet. Kirkwall and Prestwick have already received close to one and a half times their average September rainfall, while at Achnagart in the Highlands rain has been recorded every single day for the past 27 days.

Northern Ireland and Wales have broadly seen their average rainfall amounts. By contrast, north-east England has experienced some of the lowest totals of the month so far. The contrast means that while farmers in the west count on a wetter autumn, growers in the east face continued concerns about parched ground and the effects of long-term drought conditions.

That imbalance matters for water supply planning, and forecasters note the pattern of a dry south and east alongside a wet north-west and west is likely to continue to shape conditions in the week ahead. The approaching Atlantic depression is the main near-term concern, and its timing will determine whether England and Wales see a soaking or simply a blustery change in the air.

So the pattern for the week is clear: a cool, possibly foggy start, then a warm and sunny Monday, a very warm but increasingly windy Tuesday, a wet and gusty Wednesday in the west, and a settled return to calmer, drier weather by Thursday and Friday. For anyone enjoying the sunshine, the message from forecasters is to make the most of it — because the Atlantic is about to have its say.