Britain Basks in Late September Warmth Before Atlantic Depression Delivers Wind and Rain

Britain is set for one last burst of early autumn warmth this week, with temperatures forecast to reach the mid-20s before a change in the weather pattern brings distinctly westerly, more unsettled conditions. A vast area of low pressure sitting out in the Atlantic is expected to draw warm southerly to south-easterly winds across the United Kingdom early in the week, but for many areas the sunshine will come with a price.

According to Helen Willetts, Lead Weather Presenter reporting from the BBC Weather Centre, Tuesday is expected to be the warmest day of the week. After it passes, the combination of longer nights and a change in air direction means daytime temperatures will generally drift back towards the September average, ending what has been an unusually warm month for large parts of the country.

The approaching depression is also expected to deliver a spell of wetter and windier weather. The most unsettled conditions are forecast for Scotland, Northern Ireland and the western parts of England and Wales, where Atlantic systems have already dominated the month's weather. Central, southern and eastern England — regions that have been dealing with drought conditions — are likely to see considerably less rain from the same system.

The immediate picture is set by the seasonal changeover. Last week brought the autumn equinox, marking the point when nights become longer than days across the country. Despite the warmth of the September sun, longer nights mean the ground cools more quickly after dark, and forecasters expect noticeably chilly conditions on Monday morning. Some patches of fog are also possible, a concern for anyone heading out on the Monday commute.

Once that early mist disperses, many places should enjoy a brighter day. High pressure is forecast to allow sunny spells to develop, with only a few scattered showers breaking up the sunshine. South-east England may see some welcome rain through the afternoon and evening, although forecasters stress this is far from certain. Temperatures on Monday are expected to range from the mid to high teens, with some southern locations reaching 20C.

Tuesday brings a strengthening southerly wind and a notably warmer day in comparison. High teens are forecast for Scotland and Northern Ireland, while England and Wales can expect between 20 and 26C — a sharp rise of several degrees in many areas and the week's peak.

The price for that warmth arrives on the same day. Rain is expected to move into Northern Ireland during the Tuesday afternoon and then track slowly eastwards through the evening and night. The forecasters warn it may become persistent and occasionally heavy, accompanied by strong winds and gales on exposed coasts and hills, which could make travel conditions difficult in western areas.

Further east, drier and brighter conditions may hold on before the rain finally arrives on Wednesday, and in some places it could even linger overnight. Behind the front, the picture returns to something more familiar for autumn: sunny spells interspersed with scattered showers, with the western parts of the country still windy on Wednesday.

By Thursday, high pressure is expected to build, bringing calmer and drier conditions more widely. By Friday, the north-west becomes the focus for any remaining showers, suggesting a return to the familiar Atlantic pattern that has defined much of the recent weather. As always, the BBC Weather Centre cautions that forecast details may change, with updated local forecasts available for any area.

The context for all of this is a month that has been both remarkably warm and remarkably divided. Following the UK's hottest summer on record, September has been another notably warm month for many parts of the country — but it has also exposed a stark north-west to south-east contrast in rainfall.

Scotland and other western areas have been repeatedly hit by Atlantic weather systems bringing rain and wind, while much of central, southern and eastern England has stayed largely dry with plenty of sunshine. Rainfall totals have consequently varied dramatically, with some drought-affected parts of England receiving very little and parts of north-west Scotland being very wet.

The figures underline the split. Kirkwall and Prestwick have already recorded nearly 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. By contrast, parts of Northern Ireland and Wales have received around their average totals, and north-east England has seen some of the lowest amounts so far.

For the driest regions, the coming week is unlikely to deliver meaningful relief. With the depression tracking across the north and west and high pressure rebuilding later in the week, the central, southern and eastern areas of England look set to remain largely unaffected. Research published earlier this month found that at least seven months of relentless rain would be needed to end the drought, meaning that even a wetter week for some western districts would do little to change the broader picture.