The averaging period used for the following assessment was 1981-2010.
September started with a weak ridge of high pressure which brought dry sunny weather to many parts, although there were some sharp showers in the east. However, the rest of the month was unsettled, with an unusually high number of rain days across England in particular. Frequent north-westerly winds brought rain belts interspersed with bright showery weather until the 19th, and it was windy at times, notably on the 12th and 13th with the passage of Storm Aileen. From the 20th onwards it was generally warmer with mostly southerly winds, which brought mainly cloudy weather with rain at times and some morning fog patches.
The UK mean temperature was 12.6 °C, which is 0.1 °C below the 1981-2010 long-term average. Mean maximum temperatures were generally below normal in the south, but mean minimum temperatures were generally above normal in the north, reflecting the generally cloudy conditions. Rainfall was mostly above normal except in parts of south-east England and north-west Scotland, with over double the average amount in south Cornwall. Sunshine totals were mostly below normal, but nearer normal around the Thames Estuary and in parts of western Scotland.
The UK monthly extremes were as follows: A maximum temperature of 24.0 °C was recorded at Hawarden Airport (Flintshire) on the 4th. A minimum temperature of -1.2 °C was recorded at Altnaharra (Sutherland) on the 22nd. In the 24 hours ending at 0900 GMT on the 8th, 81.4 mm of rain fell at Honister Pass (Cumbria). A wind gust of 72 knots (83 mph) was recorded at Needles (Isle of Wight) on the 12th.
On 3rd September, western parts were windy and cloudy with some heavy rain. There were some reports of impacts from heavy rain in Cornwall, where 40-50mm fell locally in a few hours causing some flooding on roads. Rain on the 5th brought some flooding to a B road in North Wales, with reports of train delays also due to flooding. Again, on the 8th the main railway line between Bangor and Holyhead was affected by overnight rain. Across south-east Wales on the 11th there were reports of some power loss to homes, as well as some fallen trees attributed to strong winds across the area.
The first named storm of the 2017/18 season, Storm Aileen, passed over the British Isles on the 12th and 13th. There were reports across north-west England and Wales of flooding on railway lines and roads; some trees blocked railway lines, and trains were delayed, due to strong winds across England. A number of roads in Moray and the Borders were affected by flooding, with some reports of properties being flooded too. In Wales, there were reports of fallen trees damaging property and blocking roads and railway lines, as well as power outages, with some 60,000 properties without power at one point. he M48 Severn Bridge was closed in both directions, and there were delays to ferry services at Dover. On the 13th there were reports of flooding on the A90 and also in Moray.
On the 16th, surface water in the Port Talbot area resulted in some travel disruption. In Cornwall there were reports of minor flooding on roads, and heavy rain was blamed for a rock fall at Lushington Cove near Porthtowan. There were reports of damage to a hospital roof in Shrewsbury on the 18th due to heavy showers. The 19th had a foggy start for some, and the Mersey Ferries in Liverpool were suspended due to fog.
On the 20th there was persistent heavy rain in Northern Ireland. The Orchard Leisure Centre in Armagh was temporarily closed due to flooding. In Scotland, the Ayr Gold Cup horse-racing meet was abandoned due to a waterlogged course. During the remainder of the month there was fog at times, but no significant impacts were reported.
England diary of highlights
September started with a weak ridge of high pressure which brought relatively quiet weather, but the rest of the month was generally unsettled with an unusually high number of rain days. It was often cool until the 19th with frequent north-westerly winds and belts of persistent rain alternating with brighter showery weather, and it was windy at times, especially around the 10th-13th. It was warmer from the 20th onwards with mainly southerly winds, but often cloudy with some fog patches.
The mean temperature for September was 0.3°C below the 1981-2010 long-term average. Rainfall was below normal in the far south-east but generally above normal elsewhere, with over twice the average in parts of south Cornwall, and 131% of average overall. Sunshine was generally below normal with England as a whole having 86% of the average.
1st to 7th
Patchy fog cleared on the 1st leaving a sunny day, with 12.5 hours of bright sunshine at Bude (Cornwall), but showers and thunderstorms developed over eastern parts in the afternoon. There was some fog early on the 2nd, clearing by mid-morning leaving it sunny and quite warm. The 3rd started bright in the east but was otherwise cloudy with rain over the south-west spreading slowly north-eastwards, reaching the north-west and south-east but turning patchy. After a dry start to the 4th, rain spread into the north by mid-afternoon, particularly heavy over the Lake District, but it was warm with a high of 23.8 °C at Wellesbourne (Warwickshire). The temperature fell no lower than 17.0 °C at Shoeburyness (Essex) and Bognor Regis (West Sussex) early on the 5th, with rain across the north clearing away eastwards by early afternoon, scattered showers for most regions and an intense band of rain over central and eastern parts in the afternoon and early evening. The 6th was mostly dry with sunny intervals and just isolated light showers. The 7th started dry and clear in the south-east, cloudier in the west and north with patchy rain, and the rain spread to all regions through the day.
8th to 14th
Rain slowly cleared south-eastwards from southern counties on the 8th, with showers elsewhere, which turned thundery in the southern half of the country through the afternoon and produced 42.8 mm of rain at Tibenham (Norfolk). The 9th started with scattered showers in the north and west, which became widespread and thundery in southern and central regions through the afternoon. The 10th began bright or sunny in the south-east, cloudy elsewhere with showers or longer spells of rain, and the rain spread to all parts by evening. Sunshine and showers on the 11th, and the showers turned thundery in parts of the east and south-east. Sunny for most places on the 12th, with a few isolated showers in western areas, the showers becoming more widespread during the afternoon, then wind and rain reached the west by evening with a gust of 83 mph at Needles (Isle of Wight). Sunshine and widespread showers on the 13th, the showers turning thundery in the south-east, and an area of rain reached the far north-east later in the day. Showers across the west on the 14th became widespread with isolated thunderstorms from late morning, but died away in the afternoon.
15th to 19th
The 15th and 16th started dry in most places but with some showers in the north and south-west, and the showers turned widespread by evening with isolated thunderstorms in the south. The 17th saw sunshine and further scattered showers, the showers heavy in the east with isolated thunderstorms, but it remained mostly sunny and dry in the south-west. It was bright but cool on the 18th, with a high of only 10.5 °C at South Stainmore (Cumbria), with showers in places becoming more widespread, heavy and locally thundery in the south, then more persistent rain moved down from the north. Cool but bright or sunny on the 19th, with -0.5 °C recorded at Redesdale (Northumberland), but cloudier with isolated showers over East Anglia.
20th to 30th
Bright or sunny start in the east on the 20th, but with isolated showers in the south and patchy rain and drizzle in the west, the latter becoming heavier and more persistent and spreading north-eastwards. Bands of rain from Northumberland to the West Country on the 21st moved steadily eastwards, clearing the east coast after dark. Fog in the north and east early on the 22nd cleared, leaving sunshine over the south-east, but rain over the west slowly spread eastwards during the day. Fog in the south-west on the 23rd cleared, rain and drizzle elsewhere but it turned brighter and warmer from the south-west from late morning. Sunny across the east on the 24th, cloudy elsewhere with some early fog in some places, and rain in the west moved slowly and erratically eastwards through the day. Bright over the south-west on the 25th after patchy fog cleared, but generally wet with patchy fog elsewhere, the rain tending to become drizzly by evening. Extensive fog around the Midlands and south-west on the 26th cleared by lunchtime, leaving a generally cloudy day with isolated afternoon showers along the east coast. After a dry and bright start on the 27th, rain spread from the south-west during the morning, becoming more showery in the south-west later while eastern areas remained mostly dry. Mostly bright and sunny for the 28th, but some eastern parts were cloudier with showers or patchy rain dying out to leave a brighter afternoon, then rain reached the south-west later. Rain in the west on the 29th moved north-eastwards during the morning, followed by some isolated showers, with patchy rain in the south-east eventually dying out towards dusk. Rain over the west on the 30th moved erratically eastwards during the day.
Wales diary of highlights
A ridge of high pressure brought dry sunny weather at the start of the month, but otherwise it was a generally unsettled month. It was mostly cool until the 19th with frequent north-westerly winds, then warmer with frequent rain from the 20th due to mainly southerly and south-westerly winds.
The mean temperature for September was 0.2 °C below the long-term average. It was a generally dull and wet month with 147% of average rainfall and 83% of average sunshine for Wales as a whole, but rainfall was below average in the far south-east.
1st to 6th
It was dry and bright on the 1st, following a cold start with 1.2 °C recorded at Sennybridge (Powys), with the best of the sunshine in western areas. The 2nd started fine and bright, and it remained dry but clouded over from the west by mid-afternoon. A slow-moving area of heavy rain affected all parts on the 3rd, especially the north, clearing by late afternoon. It was mostly overcast but warm on the 4th with some patchy rain along the north coast, and Hawarden (Clwyd) reached 24.0 °C. After a notably warm night with temperatures no lower than 16.7 °C at Pembrey Sands (Dyfed), showers affected all regions during the 5th, intensifying in the early afternoon and clearing eastwards by late afternoon. The 6th started overcast, but cloud cleared by midday leading to a sunny afternoon, particularly in coastal areas.
7th to 12th
The 7th was overcast, and showery rain spread to all parts during the day. The 8th was a day of sunshine and scattered showers. There was sunshine and scattered showers on the 9th, the showers clearing many areas away from the west during the afternoon. It was wet on the 10th with rain or showers in most parts and 53.0 mm of rain fell at Capel Curig (Gwynedd). Sunshine and showers for the 11th, but the showers became less frequent by evening. It was bright or sunny with showers on the 12th, but turned very wet and windy by early evening ahead of storm Aileen, and Mumbles (West Glamorgan) recorded a gust of 74 mph.
13th to 19th
After a bright or sunny start for the 13th, showers became widespread, locally heavy and thundery across the west. Sunshine and showers on the 14th, with isolated thunderstorms developing late in the day, and the temperature only reached 12.3 °C at Lake Vyrnwy (Powys). Cool and wet with showers or longer spells of rain on the 15th and the temperature again restricted to a high of 12.3 °C at Capel Curig (Gwynedd). After a wet morning on the 16th, it dried up for a time before more showers developed for the west and south in the afternoon. Mostly bright or sunny on the 17th, though with scattered showers in the north at first and elsewhere during the afternoon. A sunny start in the south and west on the 18th, with scattered showers in the north spreading to most parts during the day, with isolated heavy thundery showers in the south-east. Sunny on the 19th, particularly at St Athan (S Glamorgan) with 10.7 hours, but clouding over in places with some isolated light showers later.
20th to 30th
A bright start on the 20th, but isolated patchy rain over the west became more widespread during the day, heaviest in the south. It was generally wet on the morning of the 21st, but the rain cleared eastwards to leave a mixture of sunshine and showers. The 22nd started bright but it turned wet and windy by midday. Generally dull and drizzly during the morning of the 23rd but it turned sunny from the south in the afternoon. Cloudy on the 24th and turning wet everywhere by late afternoon. Foggy over the north until noon on the 25th, bright and dry across the south-west, with rain across the east slowly clearing. Fog in central and northern areas on the 26th cleared by mid-morning, leaving a cloudy, dry day. Dry but cloudy start on the 27th, with rain, occasionally heavy, especially over higher ground, moving in from the south-west during the morning, reaching all areas by mid-afternoon, but clearing and turning more showery by evening. Bright and sunny on the 28th, but isolated showers developed in the north-west, and cloud increased during the afternoon. Bright or sunny on the 29th, any overnight rain clearing quickly from eastern areas; scattered showers developed, some heavy and thundery, but mostly dying out by late afternoon. Cloudy with showers in the morning of the 30th, and turning very wet everywhere by early afternoon.
Scotland diary of highlights
September started with a weak ridge of high pressure which brought sunny and mostly dry weather, but the rest of the month was generally unsettled. It was mostly cool between the 6th and 18th with frequent north-westerly winds, but from the 19th onwards, with mainly southerly winds, most days were warmer.
The mean temperature for September was 0.3 °C above the long-term average, but the positive anomaly was due to high overnight minima. Rainfall was slightly below normal in much of the north-west and the Central Belt but above normal in the north-east and south-west, totalling 104% of average overall. Sunshine was 90% of average, being near average in north-western parts but below average in the east.
1st to 7th
The 1st was a sunny day with showers in the morning, turning dry in the afternoon. It was generally dry on the 2nd, with sunny intervals for most and 11.5 hours of bright sunshine recorded at Kinloss (Morayshire). A band of rain moved slowly north-eastwards over the south and west on the 3rd, but it was sunny and quite warm in the north-east with a high of 20.6 °C at Kinloss (Morayshire). A slow-moving band of rain affected all parts on the 4th, and the west coast and Northern Isles had the heaviest precipitation with intensities of up to 6 mm/h recorded in Shetland. A wet morning on the 5th for the south and near the west coast, but drier in the afternoon with some sunny spells developing. Showers affected western and central regions on the 6th, but the east remained mostly dry with just isolated showers. The 7th was generally overcast with rain or showers in all regions through the day.
8th to 12th
There was a mixture of scattered showers and sunny spells in all regions on the 8th. Scattered showers in the east on the 9th, clearer in the west with sunny spells and also brightening up in the south during the afternoon, although the north remained cloudy. Rain or showers on the 10th became particularly heavy from the west during the afternoon. Persistent rain was slow to clear in the north-east on the 11th, mostly dry elsewhere, but showers became widespread, heaviest in the west. The 12th started sunny in the east but was otherwise cloudy with isolated showers, and rain spread into the south-west by evening ahead of storm Aileen which produced 64.0 mm of rain at Cullen Bay (Morayshire).
13th to 18th
Cloudy and wet across the east on the 13th, brighter elsewhere with showers. Sunshine and showers on the 14th. The 15th was bright across the south, but cloudy elsewhere with showers, especially over the north-east, which became widespread by evening. Generally cloudy and cool on the 16th with showers across the north-east and rain across the west merging to give a wet afternoon, and temperatures only reached 9.8 °C at Carterhouse (Roxburghshire). It was mostly cloudy on the 17th, but sunnier in the south, with showers especially over the north-east and also affecting southern parts later. It was mostly cloudy on the 18th, though sunny in the far west, with scattered showers in the east and rain in the north, both spreading south-eastwards during the afternoon.
19th to 30th
The 19th was dry, bright and sunny, occasionally cloudier in the far west and the Northern Isles It was mostly cloudy on the 20th, with patchy rain and drizzle in the south-west and west which spread eastwards during the day, becoming more widespread, persistent and heavy later. Generally wet on the 21st; the rain spread eastwards but became confined to the north-east by evening. It was cold overnight into the 22nd with a minimum of -1.2 °C at Altnaharra (Sutherland), the month’s lowest, and rain in the west spread to all parts during the afternoon. Early fog in the south-east on the 23rd cleared, and it was sunny across the north-east but cloudy and drizzly elsewhere. Generally cloudy on the 24th with a slow-moving band of rain through the spine of the country, heavy at times. It was sunny over the west on the 25th, but with rain for the north and east with persistent fog along the coast. Patchy fog around coasts on the 26th cleared by mid-morning to leave a cloudy day with patchy drizzle. The 27th started warm and mostly dry, temperatures no lower than 15.5 °C at Achnagart (Ross & Cromarty), with some sunshine in the north and east, but rain moved in from the south-west during the afternoon. Bright and sunny on the 28th, but windy with gusts of 60 mph at South Uist (Western Isles), and there were scattered showers before rain moved into the west from late afternoon. Rain over northern and eastern areas on the 29th, heavy in places, persisted in the Northern Isles but cleared elsewhere, followed by sunshine and scattered showers, the showers heavy and locally thundery in the west and south-west. The 30th brought sunshine and showers.
Northern Ireland diary of highlights
September started with a ridge of high pressure but the rest of the month was generally unsettled with frequent rain or showers. From the 6th until the 18th it was often cool with bands of rain interspersed with brighter showery weather, then after a brief quiet interlude, the last third of the month was warmer with frequent southerly winds, but mostly cloudy and wet.
The mean temperature for September was 0.4 °C below the long-term average. It was a wet month, especially in the west and south of the Province, with 160% of average rainfall overall. Sunshine was 95% of average, with near average sunshine in the east, but it was slightly duller in the west.
1st to 7th
It was bright or sunny on the 1st except in the east, where it was cloudy with showers. The 2nd started off dry for most, but rain spread into the west in late afternoon. The 3rd started wet for most, the area of rain clearing eastwards by midday to leave scattered showers, and it became quite warm with 21.2 °C recorded at Derrylin (County Fermanagh). It was warm overnight into the 4th with the temperature falling no lower than 16.0 °C at Magilligan (County Londonderry), and patchy rain affected all parts throughout the day. There were scattered showers with some sunny spells throughout the day on the 5th. The 6th was a cloudy and showery day, and the 7th was overcast with some rain, heaviest and most persistent in the west.
8th to 16th
The 8th started with sunny spells, before showers spread to all regions. Scattered showers and sunny spells throughout the day on the 9th. Generally cloudy on the 10th with showers becoming progressively heavier during the day. Sunshine and showers on the 11th, the showers heaviest and most frequent in the morning. After a bright start on the 12th, with a few isolated showers, it turned very wet ahead of storm Aileen. The 13th started mostly bright and sunny, but showers became widespread into the afternoon. Sunshine and scattered showers on the 14th, but clouding over later in the afternoon. More sunshine and showers on the 15th. The 16th began cloudy but dry, but turned wet everywhere before midday, restricting the temperature to a high of only 10.4 °C at Lough Fea (Londonderry), Glenanne (Armagh) and Altnahinch Filters (Antrim).
17th to 21st
The 17th started with a frost in some places, and -0.2 °C was recorded at Lough Navar (Fermanagh); it became a bright or sunny day, turning cloudier for most during the afternoon but Magilligan recorded 11.3 hours of bright sunshine. Dry and sunny on the 18th, but clouding over in late afternoon. The 19th started bright or sunny, especially in the north and east, then it became cloudier with isolated patchy rain in the west. It was cloudy on the 20th, with patchy rain becoming heavier and more persistent during the day. Early rain in the east cleared on the 21st to leave a sunny day with just isolated afternoon showers.
22nd to 30th
It was very wet for most of the 22nd but dried up by evening. Dull on the 23rd with persistent rain or drizzle through the day, and the 24th was similar before brightening up with showers from late afternoon. Many places saw fog on the morning of 25th but this cleared by noon leaving a sunny afternoon. Patchy morning fog quickly cleared on the 26th leaving a mainly cloudy day but with some sunny spells. Starting dry for most on the 27th, but rain quickly moved in from the west, showery at first, becoming very heavy in some places and amounting to 32.2 mm at Murlough (County Down). The 28th started dry but mostly cloudy, but rain, heaviest in the west, spread across all parts during the afternoon, accompanied by gusty winds with 53 mph gusts recorded at Magilligan. Bright or sunny on the 29th, but scattered showers broke out in the west in late morning and spread eastwards during the afternoon, the showers heavy and locally thundery. Sunny with a few isolated showers on the 30th.