BBC monthly outlook
Summary
Changeable, often wet weather for a time
Wednesday 8 September to – Sunday 12 September
Showers at first with a drier, cooler weekend
A wetter end to the week is in store for most of the UK eventually, with some thunderstorms and heavy showers moving through to close out the working week. Temperatures will quickly moderate from a very warm midweek, dropping to nearer the seasonal norm by the weekend.
Hurricane Larry, meanwhile, should help build a ridge of high pressure that will push in from the west over the weekend, sending lows into Scandinavia. This will bring some drier but cooler weather for much of the UK, but a chance of rain remains for the south and east of England.
Monday 13 September to – Sunday 19 September
Dry and cool start, rain chances growing later
Our alternate scenario from Friday's outlook is now the more likely forecast for next week, with Hurricane Larry tracking near Newfoundland before heading north to Greenland this coming weekend. This sends high pressure into the UK which should then travel slowly eastward into central Europe and eventually Scandinavia.
The UK should expect a largely dry but cool start to the week, with temperatures widely a few degrees below normal. This will bring some crisp, decidedly autumnal mornings, especially in rural areas. Later in the week, the forecast is still quite tricky. High pressure is likely to be lurking nearby to the east, with low pressure systems drifting slowly around western Europe. We could see a rather wet second half of the week if these lows are able to get into the country from the south and south west.
However, if high pressure wins out, we may stay mostly dry with temperatures near or a bit below average. At the moment we are favouring the low pressure moving in from the south-west, bringing some warmer air and a chance of rain to the southern half of the country. High pressure could become more likely to linger if we see a tropical cyclone in the western Atlantic early in the week. This is looking increasingly likely, but we are currently expecting this feature to be weak and bring minimal disruption.
Monday 20 September to – Sunday 3 October
Wet and cool for a time but potentially dry later
Closing out September and heading into October, we can expect large scale low pressure over north-west Europe for a while, bringing unsettled weather. High pressure in the Atlantic and Russia should tend to build in late September, and Atlantic high pressure may be aided by further tropical cyclones in the tropics.
After an initially unsettled, cool, and changeable pattern, weather fronts should become less frequent and weaker as October nears. The low pressure trough should be deflected to the north or east, taking the wettest and coolest weather with it. Weak fronts may still get into northern or eastern parts of the UK, especially Scotland, so it may stay cloudier and a bit wetter there. Eventually, high pressure is likely to build in from the south or west again, and there are some signs that early October may be a little drier and warmer than normal.
Confidence is still rather low in the forecast, thanks to an expected very active Atlantic hurricane season. We may see a bit of a lull in development over the next week or so, but by late September and into October more tropical cyclones are likely, and these could cause some disruption to our weather if they get too far north or east.
Our forecast is sensitive to the location of high pressure to our west, and tropical cyclones tend to cause this to move about more than it should normally. We could see a much drier and warmer end to September if high pressure is more influential, and this is more likely if we see hurricanes in the central or North Atlantic.
Further ahead
While keeping a close eye on Atlantic hurricanes, we will lift the veil for the first week of October and see if the drier, warmer pattern is set to persist.
https://www.bbc.co.uk/weather/outlook