UK enjoys late September warmth before Atlantic low brings gales and heavy rain

Britain is set for one last spell of notably warm weather this week before a broad Atlantic depression sweeps in, bringing wind, rain and wilder conditions to much of the country. The driver is a vast area of low pressure sitting out in the Atlantic, which is expected to pull warm air northward across the UK on a strengthening south to south-easterly flow.

According to Helen Willetts, Lead Weather Presenter at the BBC Weather Centre, the warm spell will peak on Tuesday. After that, temperatures are expected to ease back toward something closer to the average for September, a reminder that the country has already had an exceptional run of warm months.

Monday, however, will not be the day to ditch the coat entirely. The autumn equinox passed last week, meaning nights are now longer than days, and although daytime sunshine has a September feel about it, clear skies allow heat to escape overnight. Forecasters are warning of notably chilly starts to Monday morning, with patches of fog possible — a hazard for anyone commuting, and a reminder that the warmest afternoons no longer guarantee mild mornings.

Once that fog lifts, high pressure is expected to deliver a brighter day for much of the country, with sunny spells and only a few scattered showers. South-east England may pick up some useful rain during Monday afternoon and evening, though forecasters stress this is far from certain. Temperatures on Monday are expected to run from the mid to high teens, with some southern locations reaching 20C.

The real change arrives on Tuesday, when a strengthening southerly wind is forecast to deliver a much warmer day. Scotland and Northern Ireland are expected to see temperatures in the high teens, while England and Wales could reach anywhere between 20C and 26C — a spell of warmth that would make for an uncomfortable final week of the meteorological summer's shoulder season.

Rain, however, will not be far behind the warmth. It is forecast to push into Northern Ireland during Tuesday afternoon before tracking slowly eastwards through the evening and night. The Weather Centre warns it could turn persistent and occasionally heavy, accompanied by strong winds, with gales possible for exposed coastal areas and hills. Areas further east are likely to hold on to drier, brighter conditions through Tuesday, but the rain is expected to arrive on Wednesday — and may well linger into the overnight period.

Beyond the front, Wednesday brings a return to sunny spells and scattered showers, with the west still notably windy. By Thursday, high pressure is expected to rebuild, bringing calmer and drier conditions, and by Friday the north-west becomes the focus for any remaining showers. Forecasters add the standard caveat that these details may change, and encourage readers to check the latest short-term outlook for their area.

Behind the short-term picture is a broader story of a September that has been warm — but strikingly uneven. Following the UK's hottest summer on record, September has been another notably warm month for many parts of the country, yet it has also exposed a stark north-west to south-east contrast in rainfall.

Scotland and other western regions have been repeatedly hit by Atlantic weather systems bringing rain and wind, while much of central, southern and eastern England has remained largely dry, with plenty of sunshine in return. The result has been a dramatic divergence in rainfall totals: some drought-affected parts of England have seen very little, while parts of north-west Scotland have been exceptionally wet.

Some individual locations have already recorded nearly one-and-a-half times their average September rainfall. Kirkwall and Prestwick are among them. At Achnagart in the Highlands, rain has fallen on every one of the past 27 days without exception. By contrast, parts of Northern Ireland and Wales have picked up broadly average rainfall totals, and north-east England has seen some of the lowest amounts so far.

That imbalance matters, because it sets up an uncomfortable picture for anyone hoping for relief from drought. Much of the country is about to get a soaking, but for many central, southern and eastern areas — the very places that have been parched — the approaching depression is expected to deliver far less rain. Research published earlier this month suggested that at least seven months of relentless rain would be needed to end the drought, underlining how limited the immediate benefit of this week's weather will be for dry-hit regions.

So the week ahead offers a brief, uneven taste of what many will be hoping for more of: warmth, sunshine and a breeze from the south. For western Britain and Northern Ireland, that warmth comes with an Atlantic price tag in the form of heavy rain and gales. For the drought-stricken east, the contrast between a warm, settled autumnal week and the long-term rainfall deficit is likely to be as striking as the temperatures themselves.