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September 2012

The averaging period used for the following assessment was 1981–2010.

UK overview

The first half of September was fine and reasonably warm, except in north-western areas, but the month became progressively more unsettled and quite cool for all of the UK. A notably deep depression brought large amounts of rainfall and high winds to many areas from the 23rd to the 26th. The second half of the month was cooler than the first, even relative to normal, with a few overnight frosts in the north.

The UK mean temperature was 0.7 °C below the 1981-2010 average, and it was provisionally the coolest September since 1994. Despite all the rain during 23rd to 26th, rainfall totals for the whole month were only close to average for many regions, with the exception of north Wales, northern England, southern Scotland, and the east of Northern Ireland which received well above the long term average. However, with plenty of fine, settled weather in the first half, sunshine totals were above normal, notably across central and eastern England, with more than 120% widely.

A maximum temperature of 29.3 °C was recorded at Writtle (Essex) and Cambridge on the 9th. A minimum temperature of -4.1 °C was recorded at Braemar (Aberdeenshire) early on the 23rd. In the 24 hours ending at 0900 on the 25th, 97.8 mm of rain fell at Ravensworth (North Yorkshire). A wind gust of 72 mph was recorded at Inverbervie (Kincardineshire) during the 25th.

Weather impacts

The Paralympics took place in early September, enjoying generally fine weather, with temperatures reaching the mid-20s over the closing weekend (8th/9th).

In stark contrast, an unusually vigorous area of low pressure brought very unsettled weather to most parts from the 23rd to the 26th, giving particularly high rainfall totals (most notably 130 mm at Ravensworth, North Yorkshire, over a 3-day period) and some strong winds. Prolonged heavy rainfall across SW England overnight 23rd / 24th resulted in some transport disruption, with localised flooding of roads, and main rail routes closed for a time. During the 24th, the heavy rain moved north, bringing disruption to road and rail journeys in the West Midlands, North Wales and northern England. On the 25th, strong winds in eastern Scotland resulted in fallen trees, power cuts, and restrictions on road bridges. Rail services on the East Coast mainline and roads and properties in NE England were further affected by flooding. By the 26th, there were concerns about the rising levels of rivers across northern England, such as the River Ouse at York, and also across north Wales. Around 600 homes and businesses were reported to have been flooded across England and Wales since the 23rd.

England diary of highlights

The first half of the month was relatively settled, with warm, sunny days but some chilly nights, as high pressure influenced the weather particularly in the south. It was less settled in the north-west. Thereafter it became colder and the first air frosts were reported in prone spots during the second half of September. A vigorous low pressure system brought heavy rain and strong winds across much of the country from 23rd to 26th.

The mean temperature was 0.8 °C below the 1981-2010 average and it was provisionally the coolest September since 1994. Rainfall totals were near average in many areas, but it was wetter than normal across much of northern England with more than double the average in parts of the north-west and north-east. It was a sunny month across much of eastern, central and southern England with more than 120% of average sunshine widely.

1st to 4th:
The month began with alternate days bringing alternate weather. It was largely fine with some warm sunshine on 1st, but then a band of cloud and patchy rain moved south across the country on 2nd with cloudy and misty conditions in the south, though it brightened up further north. After a misty start on 3rd, it became mainly fine and sunny once again, but another band of cloud and patchy rain spread south on 4th.
5th to 8th:
High pressure dominated in the south throughout this period, with clear, chilly nights, as well as some mist and fog patches, then dry and fine days. However, the north was often cloudy, and so milder by night, with the odd spot of drizzle.
9th to 20th:
It was generally more unsettled through this period, with rain or showers, particularly over the north-west, with the south-east holding on to the best of the drier, brighter conditions. Some days were warm, with the highest temperature being 29.3 °C at Writtle (Essex) and Cambridge on 9th.
21st to 26th:
A band of rain moved south across the country on 21st, with a few heavy bursts, but the 22nd was largely dry and fine. A vigorous area of low pressure moved northwards across the UK on 23rd to 24th and remained over the UK for the next two days, resulting in wet and windy weather throughout. Southern England bore the brunt of this at first, then from 24th to 26th the highest rainfall accumulations caused localised flooding over some northern parts of England. Over the 3-day period of 23rd to 26th, Ravensworth (North Yorkshire) received 130.8 mm, of which 97.8 mm fell in the 24 hours to 0900 GMT on 25th.
27th to 30th:
Sunny spells and showers were seen on 27th, then a fragmenting band of cloud and rain moved south across the country on 28th. It was mainly fine again on 29th, after a chilly start (4.0 °C at South Newington (Oxfordshire)). Another band of rain moved in from the north on 30th, heavy in places and accompanied by strong winds.

Wales diary of highlights

After a relatively quiet, uneventful first three weeks, some autumnal weather arrived with the first notable storm of the season. From the 23rd a deepening depression affected the UK, with the unseasonably deep low centre moving across Wales on the 25th and 26th bringing heavy rain.

The mean temperature was 1.0 °C below the 1981-2010 average and it was provisionally the coolest September since 1994. Rainfall totals were near average in south Wales but above average further north, and particularly across north-east Wales. Sunshine totals were somewhat above normal.

1st to 4th:
The start of the month saw alternate days of fine then unsettled weather, with bands of rain moving south or south-eastwards across Wales, and drier conditions in between. Daytime temperatures were close to or slightly above average.
5th to 9th:
High pressure dominated during this period, leading to dry and fine conditions with mostly light winds. This meant that nights were chilly; on 5th the temperature around dawn at Sennybridge (Powys) was 2.8 °C, then overnight on 9th at Lake Bala (Gwynedd) the minimum was 3.6 °C. Overnight mist and fog patches often developed. Daytime temperatures were close to the seasonal average.
10th to 22nd:
Occasional bands of rain moved across Wales, sometimes heavy, with some settled spells of weather in between, but also periods of showers as well. It was often breezy, and on 14th it was generally windy at low levels, with gales over the highest ground. . Thunderstorms occurred on 18th in the afternoon. Maximum temperatures were generally close to or slightly above average: Cardiff Bute Park reached 20.1 °C on 13th and 18.3 °C on 21st.
23rd to 26th:
Rain spread north across Wales during 23rd, becoming locally heavy and thundery. This rain persisted through 24th and 25th, still heavy and prolonged in places, especially across northern and eastern areas. In the 24 hours from 00 GMT on 24th to 00 GMT on 25th 20 to 40  mm of rain widely fell, and Rhyl (Denbighshire) received 66 mm. During the following 24 hours another 22 mm of rain fell at Rhyl. The rain was accompanied by strong and gusty winds, helping to keep temperatures below average. On 26th the low centre moved south across Cardigan Bay and then south Wales. The wind eased across Wales, with slow-moving bands of showers. These were often thundery and locally torrential, with 21 mm falling at St. Athan (Cardiff) in the 24 hours from 00 GMT on 26th. Later on 26th most of the showers moved away south-eastwards.
27th to 30th:
Although there were some showers around, and occasional bands of rain moving across Wales, the month ended relatively quiet, with temperatures generally close to or a little below average.

Scotland diary of highlights

The month began generally dry and quite warm, but became much more unsettled and cooler towards the middle of the month, remaining autumnal and changeable until the end. An autumn storm from 24th to 26th brought heavy rain and strong winds to eastern areas.

The mean temperature was 0.6 °C below the 1981-2010 average and it was provisionally the coolest September since 1994. It was a wet month across much of southern Scotland but totals were mostly nearer normal elsewhere. Sunshine totals were somewhat above normal in the east.

1st to 5th:
The 1st was generally cloudy and wet, and the Western Isles saw some heavier bursts; Lusa (Skye) recorded 30.4  mm during 1st and 2nd. The Western Isles continued wet until 3rd, although the remainder of the country was generally dry with sunny spells. It was warmer than late August, with Dyce (Aberdeenshire) reaching 25.2 °C on 3rd. The rain over the north-west on 3rd spread south-eastwards by the evening. The 4th was largely dry and sunny as high pressure built from the south-west, but the north-west was cloudier with a few spots of rain and fresh or strong south-westerly winds. The settled weather for most continued on 5th.
6th to 16th:
On 6th, rain edged into the north-west and spread south-east during the day, to leave a cloudy day on 7th with patchy rain for central and eastern areas. Although 8th began cloudy, with rain for eastern areas, it was generally dry and bright by afternoon. The 9th was bright to start, but rain spread from the west during the morning to reach eastern areas by late afternoon. Although 10th started bright for eastern areas, rain already in the north-west spread eastwards by the afternoon. The 11th started bright, but showers developed during the day, whereas the east did get more in the way of sunshine. The 12th was a generally bright day although scattered showers affected the central Highlands. Winds strengthened on 13th, with a gust of 56 mph at Altnaharra (Sutherland); heavy rain, mainly over the north-west, cleared eastwards later in the day, followed by another breezy day on 14th with a few light showers mainly for western areas. It was generally cloudy on 15th, with some patchy drizzle for central areas. The 16th saw rain in the west in the morning, spreading east in the afternoon but becoming lighter and more patchy, while the north-west saw some heavy showers.
17th to 23rd:
The 17th saw plenty of showers, many of them heavy, with thunder for the Ayrshire coast. The showers became largely confined to western and northern areas on 18th and 19th, with a cool north-westerly wind. Much of 20th was wet for areas south of the Central Highlands, with some heavy rain; the Ayrshire coast fared worst with Prestwick recording 59 mm. The rain cleared overnight to leave a drier and brighter day on 21st for southern areas although some scattered showers affected north-eastern areas. The 22nd and 23rd were generally dry with sunny spells and only a few scattered showers for the Western Isles. The night of 22nd/ 23rd was cold overnight with -4.1 °C at Braemar (Aberdeenshire).
24th to 30th:
A strong north-east wind on 24th, and rain over much of the country, kept temperatures to single figures in many areas. The heaviest of the rain was over the Borders and the south-west, with Charterhall (Berwickshire) recording 44 mm. The 25th was another day of rain and strong north-east winds, northern and eastern areas now seeing the heaviest rain, with Cluanie Inn (Inverness-shire) recording 22.8 mm; Inverbervie (Kincardineshire) recorded a gust of 72 mph The 26th saw heavy showers with thunder for Lothian and Fife in the morning spreading south-east during the afternoon to leave scattered showers in the north-east. The 27th started dry in eastern areas, but rain already in the Western Isles in the morning spread south-east during the afternoon. Sunshine and showers on 28th, the showers heaviest and most frequent in the west and north, driven on by a strong westerly wind. The showers eased and became confined to the far north-west on 29th, many other areas being dry and bright. A band of rain spread from the west early on 30th but cleared during the morning to leave a bright afternoon, with heavy showers confined to the north-west.

Northern Ireland diary of highlights

After a mostly fine start, much of the month was rather unsettled and cool with plenty of rain and showers. The 24th was a particularly cold, wet day under the influence of a deep autumn low pressure system.

The mean temperature was 0.7 °C below the 1981-2010 average, making it provisionally the coolest September since 1994. Rainfall amounts were near normal in most areas but it was a wet month across County Antrim and County Down. Eastern areas were somewhat sunnier than usual.

1st to 8th:
It was generally cloudy with rain for northern areas on 1st, clearing overnight to give a brighter and drier day on 2nd and at first on 3rd, although it clouded over from the north-west later on 3rd with some light rain by late afternoon. The rain cleared on 4th to leave a generally dry and sunny day, and the fine weather continued on 5th with temperatures reaching 19 °C in many areas. The 6th started bright, but patchy rain spread from the west during the afternoon, clearing overnight to leave generally dry and bright days on 7th and 8th.
9th to 20th:
The unsettled theme returned on 9th with rain spreading from the west in the morning reaching eastern areas later in the day. The rain continued south-eastwards, clearing during the morning of 10th to leave a bright afternoon with a scattering of showers, and 11th was similar with sunny spells and scattered showers. A damp start on 12th with patchy light rain for many areas, but this cleared during the afternoon to give a fine end to the day. The 13th was cloudy, with strengthening westerly winds and rain spreading from the west in the evening, and a gust of 48 mph was recorded at Magilligan (Co. Londonderry). The north-westerly winds eased slightly on 14th, although it remained breezy with a scattering of light showers which cleared overnight leaving a generally cloudy but dry day on 15th. A band of rain spread from the west in the early hours of 16th and cleared during the morning to leave a few scattered showers and a brisk westerly wind. A bright day followed on 17th with some scattered showers for western areas, and 18th and 19th were similar with some heavier showers for north-western areas. The 20th was very wet for most of the country, with rain slowly spreading from the north-east and only clearing south-eastwards late in the evening.
21st to 25th:
It was much drier and brighter on 21st, and the fine weather continued into 22nd with another dry and sunny day, but on 23rd a mixture of sunshine and showers returned. On 24th a strong north-east wind kept temperatures in single figures for most areas; there was widespread and at times heavy rain for most of the day with Killylane (Antrim) recording 87.2 mm. There was little improvement on 25th with more rain for most areas and again a strong north-east wind.
26th to 30th:
The 26th was a much drier and brighter day, and although 27th started dry some patchy rain edged into western areas later in the afternoon. Another day of sunshine and some heavy showers on 28th, with a strong westerly wind. Although showers were far fewer and the winds eased slightly on 29th, it remained on the cool side in the north-west wind. A band of rain spread from the northwest in the early hours of 30th but cleared by mid-morning to leave a bright and generally dry day.


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