Britain set for 25C burst of late September warmth before wind and rain return

Britain is heading for a distinctly unseasonal spell of weather this week, with forecasters expecting daytime temperatures to climb as high as 25C (77F) in parts of the country on Tuesday. The warm spell arrives at the close of a September that has already proved remarkably mild, and it is forecast to be short-lived, with unsettled Atlantic weather pushing back in behind it.

Simon King, the BBC's lead weather presenter, said the warmest conditions would be concentrated across the south-east of England, where maximum temperatures are expected to reach the mid-20s Celsius. More broadly, temperatures will widely push into the 20s across England, while high teens are expected in many other areas. For a day in late September, those numbers represent a significant departure from normal — around three to six degrees above the average for the time of year, with typical late-September maximums across England sitting in the 16 to 19C range.

The driver of the warmth is a strengthening southerly airflow. King explained that with unusually hot air in place across France and Spain, where temperatures have widely been in excess of 30C, the south-westerly wind regime will draw some of that heat northwards and funnel it into the British Isles. It is an unusually early-autumn example of the "Spanish plume" pattern, in which air that has been heated over the Iberian Peninsula and western Europe is transported towards the UK.

The day itself will not be uniformly clear. Tuesday morning is expected to bring a good deal of cloud along with a few showers, but sunny spells should develop later over England and Wales as the warm air becomes more established. Conditions will be milder than average across the other home nations too, with maximum temperatures on Tuesday of between 17 and 22C forecast for Wales, Northern Ireland and Scotland — broadly warmer than the seasonal norm, even though the highest values will be some distance short of those expected in southern England.

That warmth comes with a strengthening wind. Gusts of up to 50mph are expected in Northern Ireland and western Scotland as the southerly flow builds, a change that will be most noticeable in exposed coastal and upland locations. The windy spell is tied to a large and deep area of low pressure moving north through the eastern Atlantic towards Iceland, which is also the engine room of the warm air delivery.

Overnight conditions into Wednesday are the most unusual part of the forecast. King said warm southerly winds continuing after dark will mean minimum temperatures more typical of a summer's night than of early autumn, with values widely between 15 and 19C. In parts of south-east England, he added, it is "not out of the question" that temperatures will not dip below 20C overnight at all. For context, typical overnight minima in late September are only around 7 to 11C — a 10-degree or more gap between what is usual and what is coming.

Such mild nights have practical consequences. Hospitals and care homes in the south-east may be asked to manage heat-related pressure overnight, while household energy use for heating will be suppressed. Gardens and outdoor venues will get a late bonus day, and anyone planning an autumn walk, cycle ride or evening event will find conditions far more forgiving than the calendar suggests — though anyone heading out late will still want a layer, as the warmth fades from west to east.

The broader picture adds weight to the forecast. Every month of 2026 so far has been warmer than average, according to the Central England Temperature record — the world's longest-running temperature record, which tracks average temperatures across a network of English locations. Running up to 26 September, the CET sits 2.6C above normal, and the year to date is likewise 2.6C higher than normal.

King said it would take much colder-than-normal weather for the remainder of the year for 2026 to avoid ranking among the warmest years on record for the UK. The Met Office's latest three-month outlook, covering October to December, reinforces that impression: it indicates higher-than-normal chances of a mild autumn and the start of winter, rather than an early cold snap that would pull the annual average back down.

For those who have endured a hot, dry summer, the immediate forecast offers temporary relief rather than resolution. Separate reporting published earlier this month found that at least seven months of relentless rain would be needed to end the drought, according to research — a striking measure of how deeply the year's earlier dryness has bitten into soils and water reserves. A week of warmer-than-average nights, however pleasant for comfort, does very little to replenish those stores, and any rain that does arrive later in the week is unlikely to alter the underlying picture in one step.

The message from the forecast is therefore one of a brief, welcome Indian-summer-style bonus rather than a change in the underlying pattern. Tuesday delivers the best of it: sunny spells, daytime highs in the mid-20s across England, and a summer's night to follow in the south-east. But with a deep Atlantic low tracking towards Iceland, stronger southerly winds and a return of wind and rain are already in the pipeline, and the weather is likely to revert to more typical autumn conditions before the month is out.