The rose diagram describes the range of swells directed at Robertsport over a normal 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 coast so we have chosen the optimum grid node based on what we know about Robertsport. In this particular case the best grid node is 29 km away (18 miles).
The rose diagram shows the distribution of swell sizes and directions, while the graph at the bottom shows the same thing but without 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 occurred only 94% of the time. Green and yellow show increasing swell sizes and highest swells greater than >3m (>10ft) are shown in red. In either graph, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the prevailing swell direction, shown by the longest spokes, was WSW, whereas the the dominant wind blows from the SW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Robertsport and offshore. We combine these with the no surf category of the bar chart. To avoid confusion we don't show these in the rose plot. Because wind determines whether or not waves are clean enough to surf at Robertsport, you can load a different image that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. During a typical northern hemisphere autumn, swells large enough to cause surfable waves at Robertsport run for about 6% 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.