The figure describes the variation of swells directed at Church Bay over a normal northern hemisphere summer and is based upon 3676 NWW3 model predictions since 2008 (values every 3 hours). The wave model does not forecast wind or surf right at the shore so we have chosen the most applicable grid node based on what we know about Church Bay. In the case of Church Bay, the best grid node is 15 km away (9 miles).
The rose diagram shows the distribution of swell directions and swell sizes, while the graph at the bottom shows the same thing but lacks direction information. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. These occurred only 80% of the time. Green and yellow represent increasing swell sizes and highest 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 happens.
The diagram implies that the prevailing swell direction, shown by the longest spokes, was NW, whereas the the dominant wind blows from the WSW. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Church Bay and away from the coast. We combine these with the no surf category of the bar chart. To keep it simple we don't show these in the rose diagram. Because wind determines whether or not waves are clean enough to surf at Church Bay, you can select a similar diagram that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. During a typical northern hemisphere summer, swells large enough to cause surfable waves at Church Bay run for about 2.0% 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.