This image shows the combination of swells directed at Dockweiler Beach through an average northern hemisphere winter, based on 5048 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the shore so we have chosen the optimum grid node based on what we know about Dockweiler Beach. In this particular case the best grid node is 48 km away (30 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 represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. These were forecast only 17% of the time. Green and yellow represent increasing swell sizes and biggest swells greater than >3m (>10ft) are shown in red. In both graphs, the area of any colour is proportional to how frequently that size swell was forecast.
The diagram suggests that the most common swell direction, shown by the largest spokes, was WSW, whereas the the prevailing wind blows from the NNW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Dockweiler Beach and offshore. We group these with the no surf category of the bar chart. To simplify things we don't show these in the rose diagram. Because wind determines whether or not waves are good for surfing at Dockweiler Beach, you can view an alternative image that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. In a typical northern hemisphere winter, swells large enough to cause clean enough to surf waves at Dockweiler Beach run for about 83% 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.