Birsay Bay Surf Stats

The graph describes the range of swells directed at Birsay Bay over a normal November. It is based on 3347 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the coastline so we have chosen the best grid node based on what we know about Birsay Bay, and at Birsay Bay the best grid node is 17 km away (11 miles). The rose diagram shows the distribution of swell directions and swell sizes, while the graph at the bottom shows the same thing but without direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These occurred only 18% of the time. Green and yellow represent increasing swell sizes and red illustrates highest swells greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how frequently that size swell occurs. The diagram suggests that the dominant swell direction, shown by the largest spokes, was WNW, whereas the the dominant wind blows from the SW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Birsay Bay and offshore. We group these with the no surf category of the bar chart. To avoid confusion we don't show these in the rose diagram. Because wind determines whether or not waves are surfable at Birsay Bay, you can load a different image that shows only the swells that were expected to coincide with glassy or offshore wind conditions. During a typical November, swells large enough to cause good for surfing waves at Birsay Bay run for about 82% of the time.

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