City Beach Groyne Swell Statistics, May: All Swell – Any Wind
The graph illustrates the combination of swells directed at City Beach Groyne through an average May. It is based on 2200 NWW3 model predictions since 2007 (values every 3 hours). The wave model does not forecast wind and surf right at the coastline so we have chosen the optimum grid node based on what we know about City Beach Groyne. In this particular case the best grid node is 24 km away (15 miles).
The rose diagram describes the distribution of swell directions and swell sizes, 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 occurred only 0.3% of the time. Green and yellow illustrate increasing swell sizes and red shows largest swells greater than >3m (>10ft). In each graph, the area of any colour is proportional to how commonly that size swell was forecast.
The diagram implies that the prevailing swell direction, shown by the largest spokes, was WSW, whereas the the most common wind blows from the SE. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from City Beach Groyne 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 graph. Because wind determines whether or not waves are good for surfing at City Beach Groyne, you can view an alternative image that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. In a typical May, swells large enough to cause clean enough to surf waves at City Beach Groyne run for about 89% 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.