The rose diagram illustrates the variation of swells directed at Praa Sands through an average December. It is based on 1736 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast surf and wind right at the shore so we have chosen the best grid node based on what we know about Praa Sands, and at Praa Sands the best grid node is 14 km away (9 miles).
The rose diagram describes the distribution of swell sizes and swell direction, 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 were forecast only 72% of the time. Green and yellow illustrate increasing swell sizes and red represents the largest swells, greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how frequently that size swell happens.
The diagram suggests that the dominant swell direction, shown by the biggest spokes, was WSW, whereas the the most common wind blows from the W. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Praa Sands and out to sea. We group these with the no surf category of the bar chart. To simplify things we don't show these in the rose graph. Because wind determines whether or not waves are surfable at Praa Sands, you can load a different image that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. In a typical December, swells large enough to cause good for surfing waves at Praa Sands run for about 28% 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.