Southerly warmth peaks midweek before Atlantic fronts batter western UK

Britain is set for one final taste of summer this week before a broad Atlantic depression sweeps in from the west, but forecasters warn the unsettled weather may bypass the regions that need it most. A vast area of low pressure is expected to pull warm winds from the south and south-east across the country early in the week, delivering a spell of unseasonably mild weather — with the thermometer set to peak on Tuesday before sliding back towards the September average.

The timing of the warm spell coincides with a change in the seasons. The autumn equinox passed last week, marking the point at which UK nights are now longer than days. That matters for overnight conditions: even under a September sun, clear skies now allow heat to escape, and forecasters expect noticeably chilly starts to both Monday and Tuesday. Commuters are being warned to watch out for patches of early-morning fog, which could make for slow journeys before the day's brightness develops.

Once that fog lifts, Monday should be a reasonably pleasant day for most. High pressure is expected to hold on, allowing sunny spells to break up any cloud, with only a few scattered showers drifting through. The best of the sunshine will be found in the south-east, where some areas may also pick up a little welcome rain during the afternoon and evening — though forecasters stress this is far from certain. Temperatures are forecast to range from the mid to high teens, with parts of southern England reaching 20C (68F).

Tuesday is the day to make the most of. A strengthening southerly breeze will draw genuinely warm air up from Iberia and France, and with the wind strengthening, most of the UK should see a bright, mild afternoon. Forecasters expect high teens in Scotland and Northern Ireland, and a range of 20C to 26C across England and Wales — comfortably above the seasonal norm for late September.

The catch arrives on the same day. Rain will push into Northern Ireland during Tuesday afternoon, then work its way slowly eastwards through the evening and night. Once it arrives, the rain is forecast to become persistent and occasionally heavy, accompanied by strong winds — with gales likely on exposed coasts and hills. Conditions further east are likely to stay drier and brighter for longer, with the front not arriving until Wednesday in many areas, and possibly lingering into the overnight hours.

Beyond the front, the pattern returns to something more familiar. Once the rain clears, the UK is expected to revert to sunny spells with scattered showers, and it will remain windy in the western half of the country on Wednesday. By Thursday, high pressure is forecast to rebuild, bringing calmer and drier conditions in its wake. The end of the week looks settled for most, with the north-west of the country becoming the focus for any remaining showers by Friday.

The big question is whether the incoming weather does anything for the drought-affected parts of England. Much of the UK can expect wetter and windier weather from the approaching depression, and the most unsettled conditions are forecast for Scotland, Northern Ireland, and the western parts of England and Wales. However, forecasters say many central, southern and eastern areas of England may see far less rain — potentially missing the system almost entirely. The regions where reservoir levels and soil moisture are most depleted could therefore finish September no better off.

September itself has already been unusually warm, following what was the UK's hottest summer on record. But the month has also laid bare a stark north-west to south-east contrast. While Scotland and other western districts were repeatedly hit by Atlantic weather systems carrying rain and wind, large parts of central, southern and eastern England stayed largely dry with plenty of sunshine — producing a highly uneven picture of rainfall totals.

The figures underline just how dramatic that split has been. Some drought-affected parts of England have received very little rain for the month, while parts of north-west Scotland have been soaked. Kirkwall and Prestwick have both already collected close to one and a half times their average September rainfall. At Achnagart in the Highlands, forecasters say rain has been recorded on every one of the past 27 days.

Elsewhere, parts of Northern Ireland and Wales have received about their average for the month, while north-east England has seen some of the lowest totals anywhere in the UK. The expectation of another wet Atlantic spell landing primarily on the west, and largely missing the driest corners of England, reinforces concerns raised in earlier BBC Weather reporting, which cited research suggesting it could take at least seven months of relentless rain to end the drought.

There is also a broader implication for the autumn outlook. A warm, settled end to September followed by Atlantic westerlies would be a fairly typical British autumn pattern, but the timing of the rain matters enormously for anything still in the ground. For growers, planners and anyone watching water stocks, a front that passes overhead without delivering meaningful totals is little consolation for a warm and sunny month.

As always with a developing Atlantic system, the detail remains subject to change. Winds, frontal timing and rainfall totals can shift as the depression approaches, and forecasters are urging readers to keep checking the short-term forecast for their own area rather than relying on a week-long snapshot. The broad picture, however, is settled: a warm, bright interlude for many through Monday and Tuesday, then a wetter, windier, more changeable pattern from midweek onwards, with the west bearing the brunt of it.