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September 2018

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

The start of September was fine and warm over southern areas, but less settled further north; within a few days unsettled weather was prevalent over the whole country.  This continued for most of the month, and there was a particularly windy spell with a succession of active depressions after mid-month.  However, the last week of the month was more anticyclonic, with settled autumnal weather especially towards the south.

The provisional UK mean temperature was 12.4 °C, which is 0.2 °C below the 1981-2010 long-term average.  Temperatures were generally lowest relative to average in western areas.  Rainfall was 108% of average, though this overall figure masks significant regional variations with a few locations only having around half the average amount but much of north-west Scotland having over 150%.  Sunshine was 108% of average, and it was broadly sunnier in eastern areas than further west, with the London area having over 130% of normal sunshine.

The UK monthly extremes were as follows:  A maximum temperature of 26.5 °C was recorded at Cambridge Botanic Gardens (Cambridgeshire) on the 17th.  A minimum temperature of -3.6 °C was recorded at Katesbridge (Down) on the 29th.  In the 24 hours ending at 0900 GMT on the 21st, 78.6 mm of rain fell at Capel Curig (Gwynedd). A wind gust of 79 knots (91 mph) was recorded at Killowen (Down) on the 19th.

Weather impacts

September was a mixed month, with the arrival of the first two named storms of the 2018/19 season, Storm Ali on the 19th and Storm Bronagh on 20th to 21st, during a spell of very windy weather. There were no significant weather impacts prior to the arrival of Storm Ali on the 19th. Ex-tropical Storm Helene approached the UK on the 17th and 18th but this declined in intensity and no notable impacts were reported.

On the 19th, Storm Ali brought widespread disruption to Northern Ireland with a maximum gust of 79 knots (91 mph) recorded at Killowen, County Down. Power shortages were quite widespread with 90,000 customers losing power in Northern Ireland, 30,000 in Scotland, 15,000 in north-east England, 2000 in Cumbria and 500 in Wales. Numerous roads and rail lines were blocked and closed, especially in Northern Ireland. Ferry services were cancelled or delayed and flights were delayed and diverted. The Foyle Bridge was closed for a time, as was the M1 when a power cable came down across the motorway. One man died and there were multiple injuries from flying debris and from trees falling onto cars. In Scotland, the Tay Bridge was closed. An elderly couple were attended to by emergency services in Llandudno after they were blown over in the strong wind, and the man later died of his injuries. 

Storm Bronagh swept across England and Wales on the 20th/21st. Parts of Wales, the Midlands and the east and north-east of England were especially affected by flooding and fallen trees on roads, and a landslip onto a railway line in the Rhondda valley closed the line to Cardiff. The Humber Bridge was closed to high-sided vehicles for a time. Northern PowerGrid reported about 2000 customers lost power, and flights at East Midlands airport were diverted.

The remainder of the month was relatively quiet with no further notable weather impacts. Overnight air temperatures dipped below freezing for the first time this season in a few places.

England diary of highlights

September began settled and warm with plenty of sunshine for most eastern and central parts, but there was a long spell of predominantly westerly winds and unsettled weather starting in the second week and lasting until the 23rd, and it was often very windy between the 18th and 21st.  The rest of the month was more settled with some notably cool nights especially for the south.

The mean temperature for September was provisionally equal to the 1981-2010 long-term average.  Mean maximum temperatures were mostly above normal in the east and south and below in the north-west, and mean minimum temperatures were near or slightly below normal in all regions.  It was generally a rather wet September in the north-west but drier than average in most other regions, and rather sunny in central and eastern areas; England as a whole had 88% of average rainfall and 115% of average sunshine.

1st to 5th

High pressure brought mostly warm and dry weather but there were some slow-moving fronts.  The 1st and 2nd were dry, warm and sunny in most central and eastern parts, and the 2nd saw 12.6 hours of sunshine at several sites including East Malling (Kent) and Tibenham (Norfolk), but the west was cloudier with some light rain and drizzle.  Rain across the north-west and far south-west moved into the north-east on the 3rd but died out further south, with warm sunshine again for East Anglia and the south-east.  Most places were cloudy on the 4th with a little patchy rain and drizzle moving north-east from the Midlands and some showers in south-east England by evening.  The 5th was generally sunnier, though cloudy in the far north-east and south-east with some light rain and drizzle.

6th to 14th

A northerly outbreak on the 6th/7th was followed by an unsettled westerly type.  The south-east was dry, bright and warm on the 6th but rain spread across most other parts from the Midlands southwards and the far north had sunshine and showers, the showers locally heavy and thundery.  On the 7th, showers affected the north Midlands and eastern coasts from north Norfolk northwards, with longer spells of rain for the north-east, but most other parts were dry with sunny spells.  The 8th was cloudy and breezy, and rain in the west spread eastwards across the Midlands and north.  The 9th had some showers over the north but was mainly dry elsewhere.  A ridge of high pressure brought sunshine for the south on the 10th but it was cloudy elsewhere and rain spread into the north-west from mid-afternoon, and this rain belt moved south on the 11th, weakening as it reached southern areas, and central and northern parts became brighter.  Another band of rain started across the Midlands early on the 12th and spread slowly south, clearing the south-east by evening, and it turned brighter across the north with a few showers in Cumbria.  Central and southern parts had a dry and bright day on the 13th, but it was cloudier in the north and south-west with outbreaks of rain in the north-west.  The 14th was a cloudy day with showers in the south-west, and rain over the north moved south during the day, becoming lighter and more showery.

15th to 23rd

After a brief warmer quieter interlude the weather turned very autumnal.  The 15th was sunny in the south-east but cloudier elsewhere with light rain or drizzle in the west.  On the 16th rain over the north moved southwards, stalling over the Midlands and south-west.  The rain moved away northwards on the 17th, and it became sunny and warm across most areas, with a high of 26.5 °C at Cambridge Botanic Gardens.  Storm Helene brought very windy weather to many parts overnight 17th/18th, and the 18th saw some rain in the north during the morning, and some light rain over the south-west, but otherwise it was bright and breezy and also warm in the south-east.  Storm Ali brought even windier weather for most on the 19th, with rain in the north-west moving south-eastwards during the day and turning patchy, and some places recording gusts over 70 mph.  The temperature did not fall below 18.0 °C at Bognor Regis (West Sussex) overnight 19th/20th, and on the 20th Storm Bronagh sent a belt of rain north-eastwards across the country with 61.4 mm at Sheffield (South Yorkshire).  The 21st was a day of sunshine and blustery showers with a gust to 78 mph at the Needles (Isle of Wight).  The 22nd was a wet and unseasonably cool day in central and southern areas with a high of only 8.6 °C at Pennerley (Shropshire), but it was dry further north with some sunshine in the far north-east.  Persistent rain slowly cleared the south-east on the 23rd with sunshine and scattered showers following behind, the showers tending to die away later.

24th to 30th

The weather turned more settled, with some notably cool nights in many places.  The 24th was mostly dry, sunny and cool but with some isolated showers in the north.  The night of the 24th/25th was notably cold with frost in some places, followed by a cool and mostly sunny day but with cloudier weather and evening rain for the far north.  The 26th and 27th were cloudy and warm in the north but sunny in central and especially southern parts, and nights remained cold and locally frosty in the south.  Another brief northerly outbreak gave a mostly sunny day on the 28th apart from some morning showers along the east coast.  The 29th was sunny again following another cold night with a minimum of -2.1°C at South Newington (Oxon).  A band of cloud and light rain moved slowly south-eastwards on the 30th followed by sunshine and showers.

Wales diary of highlights

September started and ended with predominantly settled weather, and the last week was generally sunny with some notably cold nights for late September.  The period from 6th to 22nd was unsettled, wet and often cloudy with predominantly westerly winds, and it was particularly windy between the 18th and 21st.

The mean temperature for September was provisionally 0.4 °C below the long-term average.  Most parts of the country had a fairly wet month with near average sunshine, and Wales as a whole had 124% of average rainfall and 99% of average sunshine.

1st to 5th

Pressure was relatively high but there were some slow-moving fronts around.  The 1st and 2nd were mainly cloudy, with a little light rain and drizzle mainly in the west, but there was also some sunshine mainly in the south and east, and on the 2nd temperatures did not fall below 17.1 °C at Cardiff Bute Park overnight, then rose to 25.1 °C at Hawarden (Clwyd). Rain and drizzle spread south-eastwards across the country on the 3rd, slowly petering out, with dry and sunny weather following.  The 4th was sunny in the north and west but cloudier elsewhere, and most places had a fair amount of sunshine on the 5th.  Aberdaron (Gwynedd) recorded 11.8 hours of bright sunshine on the 4th.

6th to 14th

The weather turned more unsettled and a generally westerly type became established.  An area of rain and drizzle, heaviest and most persistent in the north and west, moved south-eastwards on the 6th, clearing most areas by late afternoon leaving sunny spells, and it was generally dry with sunny spells on the 7th.  The 8th was cloudy and wet, especially in the north-west, though the rain eased during the afternoon, and there was some patchy light rain on the 9th.  The 10th was a mostly dry and cloudy day, but rain spread into northern parts during the afternoon, and the rain was slow to clear southwards on the 11th, though it turned brighter everywhere by evening.  The south saw further rain early on the 12th but this cleared away leaving sunnier skies.  After a sunny start, cloud increased during the 13th with some isolated patches of light rain, and there were widespread outbreaks of rain on the 14th.

15th to 23rd

A generally westerly type was maintained, and it was stormy between the 18th and 21st.  The 15th was cloudy with outbreaks of light rain or drizzle, and the 16th saw some persistent rain, heaviest in the north and west.  The 17th started cloudy with some light rain in many places but this cleared away by midday and most places became warm and sunny during the afternoon.  Storm Helene brought windy weather overnight and on the 18th, which was a cloudy day with widespread rain early and late.  Storm Ali brought even windier weather on the 19th with a gust of 77 mph at Capel Curig (Gwynedd), and a belt of rain moved through followed by sunshine and showers and easing winds.  After a dry start in the north, persistent and quite heavy rain spread north-eastwards across all areas on the 20th, and gales developed in the south associated with Storm Bronagh; 78.6 mm of rain fell at Capel Curig (Gwynedd).  The 21st was a cooler day with sunshine and frequent blustery showers, locally accompanied by thunder. The 22nd was a wet day, especially in the south, and cold with a maximum of only 8.7 °C at St Harmon (Powys), the rain starting to clear from late afternoon.  Rain cleared the south early on the 23rd and a northerly outbreak brought a mix of sunshine and scattered showers and it remained cool.

24th to 30th

Between the 24th and 26th it was dry and sunny over most of the country, but cloudier at times in the north, with a little rain for the north-west on the 26th.  Though the nights of the 23rd/24th and 24th/25th were notably cool, it was progressively warmer by day and by the 26th daytime temperatures were above the seasonal average.  There was some patchy fog early on the 27th, which was otherwise a warm sunny day.  Another northerly outbreak on the 28th brought lower daytime temperatures but it remained dry and mainly sunny.  This was followed by another particularly cold night for late September, the temperature falling to -3.2 °C at St Harmon, and then the 29th was another sunny day.  A band of cloud and occasional light rain or drizzle spread south-eastwards across the country on the 30th, followed by brighter weather with blustery showers, the showers mostly in the north.

Scotland diary of highlights

September was a mixed month, with a few days of relatively settled weather early and late in the month, but the middle fortnight was dominated by westerly winds with plenty of rain for the north-west in particular, and it was very windy between the 18th and 21st.

The mean temperature for September was provisionally 0.4 °C below the 1981-2010 average.  Mean maximum temperatures were below normal in the west and near normal in the east, and mean minimum temperatures were generally near or slightly below normal.  It was a wet month in the north-west with many places having over 150% of the average rainfall, but it was much drier in Aberdeenshire, and it was a rather sunny month in the east but a cloudy one in the west.  Overall, rainfall was 128% of average and sunshine was 99% of average.

1st to 5th

Pressure was relatively high but there were some slow-moving fronts around at times.  The 1st was warm and bright in the north-east but cloudy elsewhere with a little light rain and drizzle in central and southern areas.  Sunshine was more widespread on the 2nd, and it was warm with a minimum of 14.6 °C at Benmore (Argyll) and Cumbrae (Bute) and a maximum of 25.8 °C at Lossiemouth (Morayshire) but patchy rain in the north-west turned more persistent later.  A belt of rain in the east and south slowly cleared eastwards on the 3rd with dry and bright weather following behind.  Under clear skies and light winds the 4th started frosty in some places, with -2.5 °C recorded at Braemar (Aberdeenshire), and most places had a sunny day with 11.3 hours of sunshine at Prestwick (Ayrshire).  After a sunny start to the 5th, especially in southern and eastern counties, rain spread from the north-west to affect most areas, heaviest in the far north. 

6th to 14th

A northerly outbreak brought a cooler day on the 6th with sunshine and showers, the showers locally heavy and thundery.  The 7th was bright in central and eastern parts but cloudier with patchy rain in the north and the far south-east.  The 8th was dry and sunny, except in the south-west where it was cloudier with a little rain, but then an unsettled westerly type dominated.  The 9th was a day of sunshine and showers, the showers heavy and frequent in the west, and on the 10th showers in the west and north were replaced by an area of persistent rain which spread east to all parts.  Sunshine and showers returned for the 11th and 12th, but with fewer showers for eastern parts.  The 13th was another showery day, and the rain turned heavy and persistent in central and western parts in the evening.  On the 14th central and southern parts turned very wet during the afternoon, with showers in most other places.

15th to 21st

A changeable west to south-westerly type dominated for much of the period and it turned stormy between the 18th and 21st.  The 15th was dry with sunny intervals in the east and showery in the west but then an area of persistent rain spread from the west during the afternoon and evening.  The rain cleared eastwards overnight followed by a generally cloudy day on the 16th with showers and longer spells of rain, but it was drier and brighter in the east.  The 17th was a very wet day in central and western areas, drizzly in the south and east, and it became windy during the afternoon.  Storm Helene brought a windy day on the 18th, especially around the coasts, with rain for most, replaced by showers for the west and south by evening.  Storm Ali brought an even windier day on the 19th with gusts to 78 mph at Dundrennan (Kirkcudbrightshire), and rain for much of the day giving 66.6 mm at Cluanie Inn (Ross and Cromarty).  This was followed by sunshine and scattered showers in late afternoon and evening, and a showery regime continued for many parts on the 20th but it was mainly dry in the east; cloud increased in the south with rain in the far south by evening.  The 21st saw the rain clear the south-east to leave a rather chilly day of sunshine and scattered blustery showers.

22nd to 30th

The 22nd and 23rd were days of sunshine and scattered showers with the majority of the showers in the north and west, and it was cool for the time of year.  The 24th had generally fewer showers, but rain spread into the far north-west towards dusk.  This was followed by a warmer but rather wet day on the 25th, with bands of rain crossing the country.  The 26th saw brightness in the south-east but other areas were dull and drizzly and it turned very wet in the north and west in the afternoon.  Rain spread south on the 27th, becoming lighter and patchier, and was replaced by showers across the north.  Another northerly outbreak on the 28th led to a cold night with frost in some places and then a mostly sunny day but with showers near north- and west-facing coasts.  The 29th was cloudier with rain spreading from the north-west although it turned lighter as it spread south.  The 30th was another day of sunshine and showers with the majority of the showers in the north and west but penetrating further south and east during the day, and the temperature only reached 8.7 °C at Dalwhinnie (Inverness-shire) and Loch Glascarnoch (Ross and Cromarty).

Northern Ireland diary of highlights

September started and ended with mostly dry cloudy weather, but the middle fortnight of the month was dominated by a changeable westerly type and it was very windy between the 18th and 21st.

Overall it was a cool month, and the month’s mean temperature was 0.9 °C below the 1981-2010 long-term average, provisionally the Province’s coldest September since 1994.  It was a dry month, especially in the east, but also quite a dull month, especially in the west, and Northern Ireland had 62% of average rainfall and 87% of average sunshine.

1st to 5th

Pressure was high, but with slow-moving fronts around and a slack south-westerly flow, it was mostly cloudy.  The 1st saw some light rain and drizzle, though sunny spells developed in the south-east.  The 2nd was a warm day and started off with some sunny intervals in the north and east but rain and drizzle moved north-eastwards in the afternoon.  The temperature did not fall below 14.9 °C at Magilligan (Londonderry) overnight 1st/2nd, and reached 22.4 °C at Katesbridge (Down) during the day.  The 3rd started sunny and dry but cloud increased from the west later in the morning bringing isolated showers and it was cooler.  The 4th saw cloud and a little rain move eastwards after a mainly sunny start, and the 5th continued cloudy with a band of showery rain moving through during the afternoon.

6th to 14th

A northerly outbreak on the 6th brought cooler brighter weather, but with showers, mostly in the north-east.  The 7th was mostly dry and bright, but cloud increased from the west, and for the next few days westerlies dominated.  The 8th was cloudy with intermittent rain, and the rain became more persistent from the west during the evening, but this cleared away by the 9th leaving a day of sunshine and showers.  An area of rain spread from the west on the 10th following a dry start, and then the 11th was another day of sunshine and showers before increasing cloud brought more general rain into the west by evening.  The 12th was another bright showery day but the showers were more scattered.  Frontal systems brought cloudy weather with showers and longer spells of rain on the 13th and 14th, and the 14th was very wet for a time in the north.

15th to 23rd

A generally westerly type continued and it turned very windy between the 18th and 21st.  The 15th had belts of rain moving across the country during the morning and afternoon with a drier slot in between, and the 16th, following a bright start for some, was generally cloudy with sporadic outbreaks of rain.  The 17th was generally cloudy with rain in the north, which temporarily cleared around midday but returned in the afternoon.  Storm Helene brought cloudy windy weather with light rain on the morning of the 18th, followed by brighter weather with a few showers, and 16.2 mm fell at Castlederg (Tyrone).  Storm Ali brought even windier weather on the 19th, with a gust of 91 mph at Killowen (Down), a new record high wind speed for Northern Ireland in September, and there was a mix of sunshine and blustery showers, merging into longer spells of rain in the west, but the showers and wind eased during the afternoon.  The 20th was unusually cool for the time of year, with a high of only 9.9 °C at Killylane (Antrim), with rain spreading from the south-west after a dry start.  The 21st had sunshine and blustery showers, the showers becoming less frequent later.  Fronts to the south brought a cloudy day for most on the 22nd but it brightened up from the north.  The 23rd saw a northerly outbreak with scattered showers but plenty of sunshine too, with Thomastown (Fermanagh) and Katesbridge (Down) both recording 8.9 hours of bright sunshine.

24th to 30th

This period was less unsettled but still often cloudy.  The 24th saw some sunshine, with just isolated showers in the west and north, but it was mostly cloudy from the 25th to 27th, with light rain and drizzle in places on the 25th and 27th but the 26th staying dry.  The 28th started bright with a few showers but cloud increased in the afternoon.  Skies cleared enough overnight 28th/29th to allow a frost in some rural areas, with a minimum temperature of -3.6 °C at Katesbridge (Down), followed by a dry but fairly cloudy day.  After a cloudy start, the 30th was a day of sunshine and showers, the showers tending to die away in the afternoon.

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