BBC monthly outlook
More settled as autumn holds off for a while
Wednesday 11 September – Sunday 15 September
A wet and windy week with a calmer, drier weekend
The rest of the working week looks rather unsettled with some rain for most of the country at times, although most often in the north. Wednesday will see a frontal system from the remnants of Hurricane Dorian slowly move through Wales and England before clearing to the south in the evening. Further north, behind the front, there will be some scattered blustery showers and sunny spells. On Thursday the remnants of Tropical Storm Gabrielle are expected to track across the central UK. This means that while the system will have fronts like a normal Atlantic weather system, it will also have some warmer, tropical air. Temperatures will be noticeably warmer than recent days for the southern half of the country.
Rain and winds will tend to be confined to Wales, the Midlands, and northern England, although southern England may see some patchy rain Thursday night. By Friday and into the weekend, high pressure will begin to build in from the south and southwest, bringing more settled weather to the southern half of Britain. A few weak fronts will likely continue to plague Scotland (and Northern Ireland at times) with cloudier skies and some patchy light rain or drizzle. It will turn rather warm in the south, particularly on Sunday with temperatures reaching the mid-twenties Celsius.
Monday 16 September – Sunday 22 September
High pressure remaining largely in charge
High pressure is expected to dominate next week, blocking any low pressure systems from reaching the UK. This will keep things calm, dry, and settled with warmer air feeding in from the southwest. The best of the dry and settled conditions will be the south, particularly the southwest. Northern areas, especially North Scotland, will see temperatures a bit closer to normal, and may see influences from occasional weak fronts bringing in some cloudier and wetter weather. Early on in the week, a weak cold front slowly crossing the UK from the north will bring in a brief spell of cooler weather and some patchy light rain to eastern areas.
Most of the polar air is expected to remain east of the UK, and western areas will stay warmer than average for mid-September. By midweek and for the rest of the week and weekend, the cooler polar air will be pushed off to the east by building high pressure, bringing temperatures back above average for eastern areas. With it being September, even though sunny afternoon highs will tend to be above average, the overnight lows will likely still feel chilly, and there is a chance of frost in known cold spots or frost hollows. Mist and fog will likely become more prevalent and could linger for a time each morning.
Monday 23 September – Sunday 6 October
Cool, but perhaps settled for a time
The end of September is expected to see settled and warm weather linger as the blocking high pressure system remains stubbornly in place over or near the UK. This will keep Atlantic weather systems closer to Iceland and into Scandinavia. As the fronts pass north of the UK, a few may be just strong enough to reach into the far north of Scotland or the Northern Isles, bringing some clouds and patchy light rain. Elsewhere there should be a good amount of dry and calm weather. This is not destined to last, however, and as we head into October, autumn will likely begin to rear its head with high pressure shifting into the Atlantic and low pressure becoming more influential.
This will mean temperatures trending cooler, and the weather becoming wetter and windier; a more typical British autumn. There is some uncertainty on exactly when this pattern shift will occur. Up until recently, forecast models have been keen to break down our high pressure system early on in October. However, over recent days, at least some of these forecast models have been reluctant to do so, keeping the largely settled spell going for longer - perhaps on in to the middle of the month. There is a 40% chance that even the first week of October could be a little warmer than average and generally more settled for all. Even with more unsettled and wetter weather, high pressure is expected to linger nearby to the south or southwest, so there should be some dry and calm interludes between frontal systems. This will be most pronounced in the south.
September is looking increasingly likely to be dry and warm, but when will autumn finally arrive in October?