This picture describes the variation of swells directed at Ocean City 8th Street through a typical northern hemisphere autumn and is based upon 5144 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 Ocean City 8th Street. In the case of Ocean City 8th Street, the best grid node is 31 km away (19 miles).
The rose diagram shows the distribution of swell directions and swell sizes, while the graph at the bottom shows the same thing but without direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These happened only 40% of the time. Green and yellow show increasing swell sizes and red represents highest swells greater than >3m (>10ft). In either graph, the area of any colour is proportional to how often that size swell occurs.
The diagram indicates that the prevailing swell direction, shown by the largest spokes, was SE, whereas the the dominant wind blows from the WNW. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Ocean City 8th Street and out to sea. We lump these in 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 Ocean City 8th Street, you can view an alternative image that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. Over an average northern hemisphere autumn, swells large enough to cause good for surfing waves at Ocean City 8th Street run for about 60% 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.