Vortex Shedding off Boreray

The prevailing wind on St Kilda is from the West or Southwest. On this occasion it was from the East. The wind from the East (right of picture) rises over the sloping side of Boreray and then falls off the steep side to form an eddy, or vortex. As each vortex is blown along it is shed from the hill and a new one formed. The clouds form on each vortex as the turbulence causes the water vapour to condense out. Thus giving this "puff" effect downwind of the island.

The colours in the photo have been exaggerated to show the clouds more clearly.