Bronte Beach Swell Statistics, December: All Swell – Any Wind
This chart shows the combination of swells directed at Bronte Beach through an average December, based on 1961 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind or surf right at the shore so we have chosen the best grid node based on what we know about Bronte Beach. In the case of Bronte Beach, the best grid node is 23 km away (14 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 occurred only 30% of the time. Green and yellow show increasing swell sizes and red shows biggest swells greater than >3m (>10ft). In each 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 largest spokes, was SE, whereas the the prevailing wind blows from the E. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Bronte Beach 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 graph. Because wind determines whether or not waves are clean enough to surf at Bronte Beach, you can load a different image that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. In a typical December, swells large enough to cause surfable waves at Bronte Beach run for about 70% 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.