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September weather

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September is often a relatively sunny month in the south east, not infrequently making up for the deficiences of the summer. True, there can be a coolness in the air in the early mornings, with dew on grass and park benches, but temperatures are still on the whole very pleasant and you can still outside and wear light clothing even in the evening.

This fine weather is due to continental highs, which keep the jetstream and its Atlantic lows (the remains of Caribbean hurricanes) to the north and west. If these highs weaken, the weather is very different - cool, grey and wet, with temperatures in the mid teens. At such times it is hard to believe that you were doing summery things like going to the beach only a few days previously. But when the sun shines, it can still be as hot as any time during the summer.

Particularly hot temperatures in September include 2023, when from the 4th to the 10th the mercury topped 30 degrees every day, reaching 33 degrees on the 7th, 9th and 10th. Following on from a relatively cool and changeable July and August, these were the hottest temperatures of the whole summer. In 2016 a week of sunny weather topped out on the 13th with temperatures of 32 degrees widely and a fifty year September record of 34.4 degrees in Gravesend. 2021 also saw two days of 30 degrees on the 7th and 8th, while 14 and 15 September 2020 managed 29 degrees.

Even late in the month 21-23 degrees is still possible, for example 23 degrees on 25 September 2023, which very unusually was followed by 25-26 degrees on 7-9 October. A very exceptional year was 2011, when hot sunny weather set in from the 23rd onwards, with temperatures reaching 27 degrees on the 28th, and 29 degrees by the 30th. What made this more extraordinary was that it followed the coolest summer in 18 years, when there had been no settled period of fine weather and temperatures had only twice briefly risen above 25 degrees. The heatwave continued until 3 October, after which temperatures abruptly fell to 14 degrees in just three days.

Evenings in September generally remain quite mild, but you do start to get some nights with single digit temperatures (2023 again being a notable exception). It is not impossible to get these right at the start of the month - as happened in 2017 and 2018 when the first two nights of September saw lows of 8 degrees, while in 2020 when they got down to 6 degrees on the 1st and 2nd, and in 2015 to 6-8 degrees from the 5th to the 8th. But generally these cold nights are isolated occurrences, with night time temperatures in the double digits still quite common even late in the month.

The golden years

There was a period at the start of the century when September seemed to be frequently sunny and stable. 2001, 2002, 2003, 2005, 2006, 2012, 2014 and 2015 all conformed to this pattern. In 2002 and 2003 there was almost unbroken sunshine - with rain on only one day in 2002, for example. In other years there was some cloud and rain, but widely scattered, with the bias being towards fine weather. September 2012 saw four cloudless Saturdays in a row (from the 8th to the 30th), a record not matched by the Sundays, which were a lot more mixed (and in one case, downright wet).

September 2015 at first looked set to continue the cool and cloudy weather of August, but on the 6th high pressure established itself and produced mainly sunny skies for the rest of the month, apart from interludes of showery low pressure from the 14th to the 18th and 21st to 22nd. This was not a hot September, however, with temperatures in the high teens at best, apart from one brief excursion into the very low 20s from the 9th to the 12th. From the 23rd onwards there was a cool easterly breeze.

In 2020, after a stormy and autumnal second half of August, September started with sun and cloud, with rain overnight from the 2nd to the 3rd. A continental high then set in, tentatively at first, with a mix of sun and cloud from the 4th to the 9th. But there was then a run of twelve sunny days, with temperatures up to 29 degrees on the 13th and 14th, and regularly in the mid 20s. Finally on the 22nd, skies clouded up during the afternoon, and from then on it was autumn, with significantly cooler and more unsettled weather (though still some decent periods of sunshine at times) for the rest of the month.

Years when it was more mixed

Years when the continental high was weaker and the weather in September more mixed include 2023, when after the 30 degree weather from the 4rd to 10th, as mentioned above (and a sunny day with 26 degree temperatures on the 3rd), there were several days of less hot sunshine and cloud, before three windless sunny days from 14 to 16 September when temperatures got up to 27 degrees. Lows to the north west then sank southwards bringing changeable windy weather and quite a bit of rain, and it seemed as if autumn had set in. But there was one more warm and sunny day on the 25th, and five more from 6 to 10 October before the curtain finally came down.

In 2016, the first day of September was the last of a ten days period of sunny weather. Low pressure then intruded from the north from the 2nd to the 5th, before a continental high returned, bringing southerly air flows and some days of hot sunshine. These culminated on the 13th with temperatures reaching 32 degrees and a fifty year September record of 34.4 degrees in Gravesend. From 16 September onwards lows were back in charge but the weather remained fairly benign for the rest of the month - often cloudy but with full sun on three days and some sun on four others.

In 2019 the first eight days saw sun and cloud, driven on a north west breeze caused by high pressure to the south west. Low pressure to the north then briefly pushed southwards, bringing cloudy and wet weather for three days. But from the 12th to the 21st the high pushed back and established itself right over the UK, bringing eight days of gloriously sunny weather, with the days both cloudless and windless, and maximum temperatures varying from 19 to 25 degrees. For the last nine days of the month westerly winds then took over, and there was rain every day and only fleeting sunshine.

In 2021, after a disappointing August (whose last week had seen high pressure centred over Scotland, bringing cloud and north easterly winds to the south east), a continental high finally established itself on the 5th, bringing four days of hot sun and temperatures as high as 30 degrees. There was a thundery breakdown on the evening of the 8th, and from the 9th to the 19th slow moving lows were in charge, producing mixed weather, with some sunshine but also some heavy rain, and temperatures still in the low twenties. Another continental high set in from 20 to 26 September bringing sunshine and fairweather cloud and temperatures up to 24 degrees, before wet and windy westerlies took over for the last four days of the month.

For the first three weeks of September 2018 southern England seemed to be always just on the line between the stormier weather to the north (including two named storms mid month) and continental highs to the south. At times it was cloudy, windy and wet (nine days of rain, but only three of them prolonged or heavy), but at other times there was quite sticky sub-tropical air and temperatures up to the mid 20s. There was some sun on 15 days and full sun on a further 11 days. The latter included two sunny days at the start of the month and a run of six days in the last week, when high pressure was centred over the UK.

In 2022 slow moving high pressure, centred first to the west of the UK and then over it, was in charge for the central 18 days of the month, with similarly static lows to the west and north west in the first week and last five days. For most of the month this produced fairly cloudy weather, though with good sunshine at times. Only one day (the 17th, a Saturday) had unbroken sunshine. Showers in the first eight days of the month turned the countryside green again after a very dry July and August, but after that they were only very occasional.

In 2008 and 2009 September started wet and windy, before reverting to mainly sunny weather for the rest of the month - on the 8th in 2009 and the 13th in 2008. In 2013 the month started sunny, with highs of 30 degrees on the 5th, before showery lows set in till the 18th. The last twelve days of the month then saw high pressure dominating, with cloudy mornings giving way to pleasant sunshine and temperatures in the high teens in the afternoon.

In 2011 the heatwave at the end of the month mentioned at the top of this page was preceded by intense lows (a former hurricane) in the first week, bringing wet and windy weather in the first week, and in the second still windy but drier conditions. High and low pressure then tussled with each other before the sunshine set in on the 23rd.

In 2017 high pressure was in charge on the first two days of the month, while from 22 September a continental high ensured the south east only got some effects of lows to the north. But generally westerlies were in charge all month, including one deep low - Storm Aileen - on 13 September. This was a very changeable month, with rain on 15 days, and full sunshine only on four. Thirteen days had some sunshine, but often this was quite fleeting, or confined to the morning with weather turning more unsettled later.

The worst September of all in recent years was 2010, when lows dominated for nearly the whole of the month, at times bringing an almost wintry feel to the weather. This was particularly true towards the end of the month when a high to the west and lows to the east brought cold northerly winds, driving temperatures down into the mid teens. There only two very brief periods of high pressure - from 1-4 and 21-22 September - and a scattering of sunny days in other parts of the month.

Evenings draw in

The evenings in September draw in at an accelerating pace: by mid month, you are shocked to notice that it is dark by 7.30pm, and by the end of the month, lighting up time is 6.50pm, though it feels like it is starting to get dark at 6.30pm. That means you start to have to keep an eye on the clock on days out in the country, though this is not yet a serious problem.

On the plus side, sunlight starts to take on that golden quality, even in the middle of the day. It starts to do that winter thing of shining into your face. In central London, the sun is low enough that most streets are in shadow by mid afternoon, while others have the sun shining straight down them.

T-shirts go back into the cupboard, along with sun hats, whose protection from the sun is no longer needed. Jackets come out. Mid month the bedclothes come rapidly back onto the bed - not just duvet, but blankets too. It starts to feel nippy in the morning when you wake up: you cosy up under the bedclothes before getting up. Later in the month you may start to think about putting the heating on, but you don’t yet. Sometimes you wear a pullover inside, but often on going out you are surprised how mild it is.

Unless it is really dry, plants or gardens no longer need watering. The ground starts can be a bit damp if it rains, but soon dries out again, and there is still very little mud on paths. Colds and other ailments return. Suddenly everyone you know seems to have something and you feel you must be next.

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