Brief late-September warmth for UK before Atlantic low brings wind and rain

Britain is set for a final helping of late-September warmth before an Atlantic weather system arrives, bringing unsettled wind and rain to much of the country, according to the BBC Weather Centre. Lead weather presenter Helen Willetts, reporting from the BBC Weather Centre, said a vast area of low pressure in the Atlantic is set to draw warm south to south-easterly winds across the UK early this week. But, she warned, for some areas the rain will not be far behind.

Tuesday is expected to be the warmest day of the week, and after that temperatures will generally return closer to the September average, suggesting the current run of warm conditions is coming to an end. Much of the UK can also expect a spell of wetter and windier weather from the approaching depression, with the most unsettled conditions likely to affect Scotland, Northern Ireland and western parts of England and Wales. However, many central, southern and eastern areas of England, which have been affected by drought, may see far less rain.

Monday morning is likely to be notably chilly. The autumn equinox passed last week, so nights are now longer than days, and that means the country is getting cooler nights even under clear skies. Forecasters are warning of some fog patches to be aware of for the morning commute, which could disrupt travel in places.

Once the fog clears, a brighter day is expected to follow for many, with high pressure allowing sunny spells and just a few scattered showers. South-east England may see some welcome rain through the afternoon and evening, but it is by no means guaranteed. Temperatures will range from the mid to high teens, with some southern areas reaching 20C.

On Tuesday, a strengthening southerly wind will bring a much warmer day in return. High teens are forecast in Scotland and Northern Ireland, and between 20 and 26C for England and Wales. The combination of strong warm winds and unseasonably high temperatures means it could feel distinctly summery in parts, particularly in western and southern districts.

Rain will move into Northern Ireland during Tuesday afternoon, and then trek slowly eastwards throughout the evening and night. It may become persistent and occasionally heavy, with strong winds and gales for exposed coasts and hills. Travellers in the west, particularly on bridges, along coastlines and in hillier terrain, are advised to be alert to disruption.

Further east, drier and brighter conditions may remain before the rain arrives on Wednesday, and the wet spell could possibly linger overnight. Behind the rain, it is back to sunny spells and scattered showers, and it will still be windy in the west on Wednesday. By Thursday, high pressure is expected to build, so conditions should be calmer and drier, and by Friday the north-west becomes the focus for any showers. Willetts cautioned that forecast details may change, and advised audiences to stay up to date with the short-term forecast for their area.

The week ahead, however, offers a sharp contrast with the wider picture for the month. Following the UK's hottest summer on record, September has been another notably warm month for many, but it has also highlighted a stark north-west to south-east contrast in rainfall. While Scotland and other western areas have seen frequent Atlantic weather systems bearing rain and wind, much of central, southern and eastern England has remained largely dry with plenty of sunshine.

As a result, rainfall totals have varied dramatically across the country. Some drought-affected parts of England have received very little, while parts of north-west Scotland have been very wet. Some locations, including Kirkwall and Prestwick, have already had nearly one-and-a-half times their average September rainfall. At Achnagart in the Highlands, rain has been recorded every day for the past 27 days without interruption.

Elsewhere, parts of Northern Ireland and Wales have had their average rainfall, while north-east England has seen some of the lowest amounts so far. That leaves England split between parched ground in the east and areas in far better shape in the west, where Atlantic systems have delivered almost daily rainfall.

For those regions already struggling with drought, even a wet week is unlikely to make a meaningful difference. BBC Weather has previously reported research showing that at least seven months of relentless rain would be needed to end the drought, underlining how deeply the deficit was cut into during the record-warm summer and reinforced by the dry start to autumn.

Willetts also pointed to the longer nights as a reminder that autumnal weather is setting in, even as the daytime warmth persists. Sunshine will still be possible, but with the equinox behind us and the Atlantic becoming more active, the settled spell looks increasingly temporary. For the driest eastern areas, that may mean the forecast rain passes largely overhead, leaving another week of below-average rainfall in the books.