The rose diagram describes the variation of swells directed at Windmills 1 over a normal December, based on 1736 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind or surf right at the coast so we have chosen the best grid node based on what we know about Windmills 1, and at Windmills 1 the best grid node is 13 km away (8 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 represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. These were forecast only 39% of the time. Green and yellow represent increasing swell sizes and red represents 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 prevailing swell direction, shown by the largest spokes, was NNW, whereas the the dominant wind blows from the E. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Windmills 1 and out to sea. We combine these with the no surf category of the bar chart. To simplify things we don't show these in the rose plot. Because wind determines whether or not waves are surfable at Windmills 1, 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 December, swells large enough to cause good for surfing waves at Windmills 1 run for about 61% 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.