This picture illustrates the combination of swells directed at Ocean Beach through an average southern hemisphere spring. It is based on 5144 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 Ocean Beach. In this particular case the best grid node is 25 km away (16 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 represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. These occurred only 36% of the time. Green and yellow show increasing swell sizes and largest swells greater than >3m (>10ft) are shown in red. In each graph, the area of any colour is proportional to how frequently that size swell was forecast.
The diagram suggests that the most common swell direction, shown by the biggest spokes, was SE, whereas the the most common wind blows from the NW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Ocean Beach 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 diagram. Because wind determines whether or not waves are good for surfing at Ocean Beach, you can load a different image that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. In a typical southern hemisphere spring, swells large enough to cause clean enough to surf waves at Ocean Beach run for about 33% 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.