Fair Isle's Climate
Introduction
Fair Isle, the most southerly island of the Shetland group (the northernmost islands of the British Isles) lies approximately 25 kilometres south-south-west of Sumburgh Head at the southern end of the Shetland mainland, and approximately the same distance north-east of North Ronaldsay (the most northerly of the Orkney islands).
Perhaps Britain’s most isolated inhabited island, Fair Isle is only some 5 kilometres by 3 kilometres in extent, roughly rectangular in shape, with a heavily indented west coast.
The landscape has been moulded by the effects of ice during the Ice Ages, with large areas of glacial till covering the southern third, which is lower, more fertile, and mostly taken up with the cultivated crofting area. The remainder is largely rough grazing and rocky moorland, rising to the 217 metre Ward Hill. Though the area around the impressive landmark of Sheep Rock on the east side has cliffs over 100 metres, the west coast, with its deep slash-like geos, offers some of the island’s most impressive scenery, with cliffs rising to almost 200 metres along the north-west coast.
Climate
Though the island lies in the north temperate zone, its climate is greatly influenced by its relatively small size and location. The climate of Fair Isle is truly oceanic in nature – and is often described as hyperoceanic (e.g. Birse 1974).
Due to the rain-shadow effect of the Scottish mountains, rainfall is not excessive but precipitation is frequent with measurable rainfall on 216 to 266 days each year. The relative humidity is the highest in Britain, and except in late spring and early summer, cloudy conditions prevail. Winters are generally mild, but frequently stormy.
Summers are cool and often windy, with a high frequency of fog. During spring and summer Fair Isle often reports the lowest daytime maximum temperature in the British Isles – even though (in May and early June) it may at the same time also be the sunniest place in the country.
At almost 60° degrees north, the climate is far from typical of what might be expected at this latitude, due to the ameliorating effect of the North Atlantic Drift. The mean annual temperature is 7.5 °Celsius, with little variation between summer and winter.
As sea temperatures do not reach their highest values until late summer, it is at this time when the maximum temperatures on Fair Isle often occur – mostly in the order of 16° or 17° Celsius. In August 1975 20.2° Celsius – the highest temperature ever recorded on Fair Isle – was reported. This was almost equalled in July 1991 when 20.1° Celsius was recorded.
During winter, temperatures can fall as low as -2° or -3° Celsius but are generally around 4° Celsius. The lowest temperature recorded is -5°.1 Celsius in February 1978, though -5.0° Celsius was also recorded in March 1992.
Ground frosts are not frequent phenomena – even in winter – but they are not unknown in summer, having been recorded in every month of the year. Air frosts are reported much less frequently and, due to a katabatic effect, virtually never under calm circumstances.
The lowest temperatures are always experienced with an outbreak of cold northerly, Arctic air, when strong winds prevent the sea from exerting the usual ameliorating effect. Under such conditions, temperatures may fall to between -4° and -5° Celsius, with the wind gusting in excess of 30ms-1, and frequent snow showers often reducing visibility to less than 1000 metres.
Because of its position close to one of the major depression tracks, the weather on Fair Isle is very unsettled.
Snow, which can be frequent – falling on as many as 70 days in a winter – does not lie long, as a change of wind direction to the south always brings milder temperatures.
Overall the prevailing wind direction is south-westerly, but there is much variation during the course of the year. During spring there are frequent south-easterly winds, gradually becoming north-easterly during May, and by June the most frequent direction is north-westerly. South-easterly is again the prevailing wind direction in autumn.
Fair Isle is probably one of the windiest lowland sites in the British Isles, experiencing gales (10 minute mean speed of 34 kt. 17.5 ms-1, or more) on an average of 58.4 days each year – with 112 gale days reported in 1979 but only 16 gale days in 1985. While periods of calm, or very light wind conditions, are very rare they can occur even in winter – but seldom last for more than an hour or two.
Trends
The long term mean masks a considerable variation in the year to year data and, while 19 years is not a long enough period to evaluate trends, there does appear to be a suggestion of a cycle in the weather of Fair Isle (possibly connected with the 10 to 11 year solar cycle?).
A mild and windy period in the mid to late seventies was followed by a cooler, less windy period for much of the eighties. Recent years have seen a return to milder and much windier conditions – with three of the last four years being the warmest ever recorded on Fair Isle, and January 1993 having a three week period of storms possibly unparalled in the past four hundred years.
On a much shorter time-scale it is also possible to see cyclical variations in the yearly weather of the island – with periods of warmth; windy, unsettled weather or cold and snow occurring on more or less the same days each year.
In earlier centuries the weather ruled the life of the island. A change in climate meant the difference between an acceptable harvest and a failed harvest; the difference between a successful fishing trip or disaster.
In more recent years it meant a full larder or making supplies last until the weather relented enough to allow the island’s mailboat the Good Shepherd to risk a trip across to Shetland for supplies and mail.
Even today, with a three or four days a week air link to Shetland, a new Good Shepherd and a new breakwater, the weather conditions continue to dominate the life of the island.
In January 1993 the Good Shepherd was stormbound for three weeks and even aircraft were unable to reach the island for ten days due to the high winds.
While agriculture and fishing may perhaps no longer be as all important as they once were, by its very nature crofting will continue to depend upon the land – and sea – for its very existence.
In the light of this, it is therefore worth noting that the Isle is still dependent on the whims of sea and air in order that the needs of its population can be satisfied. Any adverse change in climate could well make this requirement increasingly difficult to meet.
LINK - (courtsey of Dave Wheeler).
Text and photographs Copyright Fair Isle Marine Environment and Tourism Initiative. All rights reserved.
