The Small Isles climate: mild, wet and windy but with above average sunshine!
The Small Isles's climate, like the climate of Western Scotland generally is milder than that of Eastern Scotland due to the stronger maritime influence. Not only are the prevailing winds blowing from the sea but there is also the influence of the warm Gulf Stream which allows many temperate species such as Dragon Palm trees or New Zealand daisies to thrive in sheltered areas on the islands' gardens. Without the Gulf Stream, the Small isles would have a very much colder climate like Canada's Labrador where the sea freezes in winter at a similar latitude!
Averages for the Small Isles
With winds mainly blowing from the sea the annual mean temperatures are in the range 9.4 to 9.7°C in western coastal areas, similar to that found in western Ireland. The sea reaches its lowest temperature in February or early March so that on average February is the coldest month. In February the mean daily minimum temperature can go down to 1.6°C, with average winter temperature of 5 to 7°C.
Like the rest of the Hebrides, the Small Isles get very little frost: less than 25 days a year, compared with 40 days on the coast of the mainland and more than 80 over the higher ground of the Southern Uplands and Highlands. If there is snow, it rarely lies for long and always comes within the period December to March. July and August are the warmest months in the region with mean daily maxima ranging from less than 14.6°C on the highest ground to more than 18.5°C. Although in recent years, it has not been unusual to experience peaks of 25°C, instances of extreme high temperatures are rare and are associated with hot air brought from mainland Europe on south easterly winds, accompanied by strong sunshine.
Out of the 4 islands, Canna and Muck being the lowest lying islands are slightly warmer, whilst Rum mountainous peaks means a light fall in temperature due to altitude.
As the number of hours of bright sunshine is controlled by the length of day, December is the dullest month in the Small Isles whilst May and June are the sunniest, particularly the first half of the month. There is very little darkness in June, and the sky is still light at 11 pm! There is 4 hours more daylight in the Small Isles than in London at midsummer, although this is reversed in midwinter.
As low lying islands, Muck and Canna with Eigg in third pace and Rum fourth, the Small Isles are amongst the the sunniest parts of Western Scotland, where the average annual sunshine totals approach 1450 hours. Neighbouring Tiree as the lowest lying island in the Hebrides is the sunniest place in Scotland with a highest monthly sunshine total of 329 hours being recorded in May 1975!
As rainfall tends to be associated with Atlantic depressions, and these tends to be more vigorous in autumn and winter, most of the rain which falls in those seasons is from this source. During this period, the islands are also prone to convective showers caused by the relatively warm sea.
Rainfall being affected by altitude, Rum is the wettest of all the Small isles! 3000 mm a year is not an uncommon occurrence in the Small Isles with flooding when the soil becomes waterlogged. This also gives for a spectacular show of waters in spate on Eigg or Rum!
Unlike other areas of the UK, Scotland tends to remain under the influence of Atlantic depressions for much of the summer too, and the Small Isles are no exception.
It is therefore fair to say that in the Small Isles, autumn and early winter are the wettest seasons, especially from October to January, and that spring and early summer is normally the driest part of the year, especially from April to June!
Being so close to the Atlantic, the West of Scotland is one of the more exposed areas of the UK. The Small Isles thus experience their strongest winds with the passage of deep depressions close to or across the UK. The frequency and strength of depressions is greatest in the winter half of the year and this is when mean speeds and gusts are strongest.
Any wind above Force 5 can disrupt the ferry service, particularly to Muck as high wind speed mean, a high swell and difficulty in approaching the pier there without being driven by the swell onto the rocks.
Gales are certainly not unusual in the Small Isles and are an experience to behold! For wind to be classed as a gale, it must reach a mean speed of 34 knots or more over any ten consecutive minutes! The Small Isles have over 25 days of gales in an average year!
As Atlantic depressions pass by the UK the wind typically starts to blow from the south or south west, but later comes from the west or north-west as the depression moves away. The range of directions between south and north-west accounts for the majority of occasions and the strongest winds nearly always blow from these range of direction.
South-westerly wind almost always bring rain, whilst north westerly are drier. Spring time also tends to have a maximum of winds from the north east, due to the build up of high pressure over Scandinavia at this time of year. November to March have the highest mean speeds with June to August the lightest winds.