The figure describes the variation of swells directed at Buffels Bay through a typical southern hemisphere summer and is based upon 5048 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast surf and wind right at the coastline so we have chosen the best grid node based on what we know about Buffels Bay. In the case of Buffels Bay, the best grid node is 21 km away (13 miles).
The rose diagram describes the distribution of swell sizes and directions, 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 87% 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 occurs.
The diagram implies that the most common swell direction, shown by the largest spokes, was SE, whereas the the dominant wind blows from the S. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Buffels Bay 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 plot. Because wind determines whether or not waves are good for surfing at Buffels Bay, you can select a similar diagram that shows only the swells that were expected to coincide with glassy or offshore wind conditions. Over an average southern hemisphere summer, swells large enough to cause clean enough to surf waves at Buffels Bay run for about 11% 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.