Manly Swell Statistics, December: All Swell – Any Wind
The figure shows the combination of swells directed at Manly over a normal December and is based upon 2209 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 optimum grid node based on what we know about Manly. In the case of Manly, the best grid node is 29 km away (18 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 show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. These happened only 31% of the time. Green and yellow show increasing swell sizes and biggest swells greater than >3m (>10ft) are shown in red. In each graph, the area of any colour is proportional to how commonly that size swell was forecast.
The diagram implies that the dominant swell direction, shown by the longest spokes, was SE, whereas the the prevailing wind blows from the E. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Manly and out to sea. We group these with the no surf category of the bar chart. To keep it simple we don't show these in the rose plot. Because wind determines whether or not waves are good for surfing at Manly, you can view an alternative image that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. During a typical December, swells large enough to cause clean enough to surf waves at Manly run for about 18% 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.