The graph illustrates the variation of swells directed at Assateague through an average March. It is based on 1724 NWW3 model predictions since 2007 (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 Assateague. In this particular case the best grid node is 28 km away (17 miles).
The rose diagram illustrates the distribution of swell sizes and swell direction, 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 were forecast only 40% of the time. Green and yellow illustrate increasing swell sizes and largest swells greater than >3m (>10ft) are shown in red. In each graph, the area of any colour is proportional to how often that size swell was forecast.
The diagram indicates that the dominant swell direction, shown by the largest spokes, was SE, whereas the the most common wind blows from the NW. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Assateague and away from the coast. 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 Assateague, you can select a similar diagram that shows only the swells that were expected to coincide with glassy or offshore wind conditions. In a typical March, swells large enough to cause clean enough to surf waves at Assateague 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.