Manly Swell Statistics, December: All Swell – Any Wind
This picture describes the combination of swells directed at Manly through an average 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 coastline so we have chosen the optimum grid node based on what we know about Manly, and at Manly the best grid node is 29 km away (18 miles).
The rose diagram describes the distribution of swell sizes and swell direction, while the graph at the bottom shows the same thing without direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These occurred only 31% of the time. Green and yellow show increasing swell sizes and highest swells greater than >3m (>10ft) are shown in red. In both graphs, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the most common swell direction, shown by the longest spokes, was SE, whereas the the dominant wind blows from the E. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Manly and offshore. We combine 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 surfable at Manly, you can load a different image that shows only the swells that were expected to coincide with glassy or offshore wind conditions. In a typical December, swells large enough to cause good for surfing 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.