BBC monthly outlook
Often most unsettled in the north and west
Saturday 31 August – Sunday 8 September
Rather unsettled and cool and times
On Saturday, an active front will bring heavy rain to western Scotland in the morning, with further rain for much of England and Wales through the day, while the far south-east will see some dry, bright and warm weather for a time. A chilly night will follow, with frequent showers for western Scotland and Northern Ireland, and lengthy clear periods elsewhere. Sunday will be a cool day for all, with frequent showers and thunderstorms developing across north-western areas, while the south will be driest and sunniest. Many areas will be dry on Sunday night, although it will be particularly chilly as temperatures fall away under lengthy clear spells.
For much of next week, high pressure will remain to the south or south-west of the UK. On Monday, a front will bring further cloud and rain to Scotland and Northern Ireland, while the rest of the country will be dry with lighter winds and sunny spells. A warmer day in the south and south-east on Tuesday, where there will be a good deal of dry and bright weather, while it will remain wetter and cloudier in the west and north. A band of patchy rain will slide south-east overnight, leaving Wednesday as a cooler day with sunny spells and scattered heavy showers, perhaps bringing a few rumbles of thunder. Thursday looks to be particularly chilly, with further heavy showers moving in on a north-westerly flow.
By Friday and next weekend, it looks more likely that an area of low pressure will impact the country. This will bring cooler, cloudier weather with a risk of rain for many areas on Friday and Saturday, although Sunday may see more widespread dry and calm weather.
Monday 9 September – Sunday 15 September
A few chilly days, but high pressure close-by
The following week may start off with high pressure lingering close to the UK, bringing a calm, largely dry and settled start to the week, perhaps with some overnight mist and fog. However, this isn't likely to last - with high pressure most often lingering to the west or south-west of the UK. As a result, northern and north-western Britain are most likely to see occasional north-westerly bursts of cooler air bringing some showers from the Atlantic, and could occasionally catch the odd frontal system, bringing more general cloud and outbreaks of rain.
Elsewhere, lengthier periods of dry and fine weather seem more likely, although they could occasionally be broken up by cloud and spots of rain approaching from the north-west. These sporadic bursts of cooler air are likely to keep temperatures slightly below normal across the north and north-east, and it will feel particularly chilly here in areas exposed to the showers and breeze.
Monday 16 September – Sunday 29 September
Pressure slowly rising across the country
It looks like high pressure will gradually become more extensive across the country from the south-west after mid-month, although this will be a rather slow process. During the third week of September, low pressure areas are perhaps more likely to impact Scandinavia than the UK, although they could occasionally extend their influence westwards towards our shores. While confidence is rather low on the exact timing and extent of these episodes, they could bring some cooler, cloudier and wetter weather at times, with blustery showers or outbreaks of rain perhaps more likely to impact northern and eastern areas. However, the proximity of higher pressure means some lengthy drier, sunnier and warmer interludes, with these perhaps becoming more frequent later in the week.
By the final week of September, it looks like high pressure will have a lengthier stay across the UK, and this should encourage more widespread dry, warm and fine conditions to develop as breezes more frequently come from the south-west. Areas of low pressure could quickly move east across the Atlantic, mainly close to Iceland, although some rather wet and breezy weather could linger across northern and north-western Britain. However, much of the country should still experience a dry and rather warm end to the month. Forecasting the British weather at this time of the year is made especially tricky by the development of hurricanes in the tropical Atlantic, and there is about a 40% chance that we will see a wetter, windier and cooler pattern lingering across the UK by the end of September.
Will the end of September remain as a reliable source of fine, warm and settled weather?