J-Bay Swell Statistics, August: All Swell – Any Wind
The graph describes the combination of swells directed at J-Bay through a typical August, based on 1984 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind or surf right at the coastline so we have chosen the most applicable grid node based on what we know about J-Bay. In this particular case the best grid node is 50 km away (31 miles).
The rose diagram describes 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 were forecast only 10% of the time. Green and yellow represent increasing swell sizes and red shows highest swells greater than >3m (>10ft). In either graph, the area of any colour is proportional to how often that size swell happens.
The diagram indicates that the most common swell direction, shown by the longest spokes, was SSW, whereas the the dominant wind blows from the W. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from J-Bay and away from the coast. We lump these in 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 J-Bay, you can select a similar diagram that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. Over an average August, swells large enough to cause surfable waves at J-Bay run for about 90% 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.