September in the UK is settling into a familiar pattern: changeable weather, useful dry windows and no convincing sign of a long, uninterrupted settled spell. The Met Office long-range forecast points to an unsettled first half of the month, followed by a greater chance of drier interludes later in September. Temperatures are expected to stay close to average at first and may run a little above average overall later on.
The immediate picture remains mixed. Atlantic systems are continuing to push bands of rain across parts of the country, with the north and west generally more exposed to wet and windy weather. Southern and central areas can still see brighter and drier periods between fronts, but the pattern is mobile enough that plans made several days ahead may need adjusting.
For the period from 11 to 20 September, the Met Office expects changeable conditions at the start, with rain or showers moving in from the west and the possibility of stronger winds at times. There should also be dry interludes. As the period progresses, those dry spells may become longer, but a prolonged nationwide settled phase is considered unlikely. Temperatures should be broadly around the seasonal average, while clear nights can feel noticeably cool.
That combination matters because September often produces large differences between daytime and overnight conditions. A mild afternoon in London, Birmingham or Cardiff can be followed by a much fresher morning, especially inland. Coastal areas and large cities tend to hold on to warmth for longer overnight, while rural valleys can cool quickly under clear skies and light winds.
The later part of the month currently carries a somewhat calmer signal. From around 21 September into early October, high pressure may spend more time close to the UK, increasing the chance of settled spells. That does not mean a dry finish everywhere. The high may weaken towards the end of September, allowing rain, showers and stronger winds to return. The Met Office also indicates that temperatures could average a little above normal over this later period, although cool nights would still be possible during clearer conditions.
For anyone planning travel, gardening, sport or outdoor events, the practical message is to think in windows rather than in a single monthly label. September can offer excellent days, but the useful dry spells may sit between fronts rather than forming a continuous late-summer block. The west and northwest are normally the first places to feel approaching Atlantic systems; eastern and southeastern areas can sometimes hold on to drier weather for longer.
Wind is another feature worth watching. Even when rainfall totals are not exceptional, an Atlantic low can make a day feel considerably more autumnal, especially on exposed coasts and higher ground. Ferry services, mountain trips and long drives are more sensitive to wind than a simple rain symbol might suggest.
Long-range forecasts should also be read differently from a next-day forecast. At two or three weeks' range, the useful information is the balance of probabilities: whether high or low pressure is more likely to dominate, whether temperatures lean above or below normal, and whether the pattern is more settled or unsettled. Exact timings of individual rain bands only become dependable much closer to the day.
So the remainder of September looks less like a clean break into autumn and more like a gradual transition. There will be rain, occasional wind and cooler nights, but also drier intervals and the possibility of some mild or warm afternoons. The best chance of longer settled spells appears to increase later in the month, while the Atlantic remains capable of interrupting them.