Storms of force 12 (wind speeds greater than 64kt, ie 74mph) suggested by James Mackenzie in his recent letter somewhat understates the magnitude of extreme storms that have been recorded in the vicinity of Shetland.
Fast-moving and rapidly-developing depressions are the main cause of severe winds in Shetland of which the New Year’s Day Storm of 1992 is an extreme example. This storm brought with it sustained wind speeds of 90 to 103kt (104 to 125mph) with gusts in excess of 150kt (172mph). This event led to widespread damage and sadly caused two deaths by blowing a hut and its occupants over the cliffs at Hermaness.Similarly, on 7th March 1997 a storm produced a sustained wind speed of 97kt (112mph) with gusts 130kt (150mph) across Faroe.
These wind speeds are comparable to those of a Category 3 hurricane on the scale used to describe hurricanes forming in the Caribbean. Hurricanes of Category 3 and higher on this scale are described as major hurricanes carrying the warning “Devastating damage will occur”.
It would be reasonable to expect that such storms would produce extreme waves of 25 to 30 metres to the west of Shetland. Waves of this magnitude have been recorded in association with severe storms.
It is not only fast moving depressions that can produce phenomenal seas but very deep lows can become slow moving in mid-Atlantic to sustain severe winds and seas for prolonged periods.
A deep mid-Atlantic low of January 1993 was of exceptional significance, not just for the wreck of the oil tanker Braer, but for the phenomenal incidence of gales that generated the heavy seas which cleaned up much of the oil spill. There were 25 days of gale force 8 or above recorded for the month with 18 consecutive gale days from the 1st to the 18th. On 10 of these days winds of storm force 10 or more was recorded.
One cannot help but wonder how Shetland’s “community investments” would have fared if the proposed wind and wave farms had been in existence during these periods of extreme weather.