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Birsay Bay ratings
Quality on a good day: 4.0
Consistency of Surf: 3.0
Crowds: 4.0

Overall: 4.2

See all 18 ratings

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Surf Report Feed

Birsay Bay Swell Statistics, May: All Swell – Any Wind

This chart illustrates the combination of swells directed at Birsay Bay through an average May, based on 2838 NWW3 model predictions since 2007 (values every 3 hours). The wave model does not forecast surf and wind right at the coast so we have chosen the most applicable 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 illustrates the distribution of swell directions and swell sizes, while the graph at the bottom shows the same thing but lacks direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These happened only 28% of the time. Green and yellow represent increasing swell sizes and largest swells greater than >3m (>10ft) are shown in red. In both graphs, the area of any colour is proportional to how commonly that size swell occurs.

The diagram implies that the most common swell direction, shown by the longest spokes, was WNW, whereas the the most common wind blows from the S. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Birsay Bay and out to sea. We lump these in with the no surf category of the bar chart. To keep it simple we don't show these in the rose plot. Because wind determines whether or not waves are clean enough to surf at Birsay Bay, you can select a similar diagram that shows only the swells that were expected to coincide with glassy or offshore wind conditions. In a typical May, swells large enough to cause surfable waves at Birsay Bay run for about 72% of the time.

IMPORTANT: Beta version feature! Swell heights are open water values from NWW3. There is no attempt to model near-shore effects. Coastal wave heights will generally be less, especially if the break does not have unobstructed exposure to the open ocean.