Coastguards Swell Statistics, Winter: All Swell – Any Wind
The figure illustrates the variation of swells directed at Coastguards over a normal northern hemisphere winter. It is based on 6363 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the shore so we have chosen the most applicable grid node based on what we know about Coastguards. In the case of Coastguards, the best grid node is 21 km away (13 miles).
The rose diagram shows 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 57% of the time. Green and yellow represent increasing swell sizes and red represents largest swells greater than >3m (>10ft). In each graph, the area of any colour is proportional to how commonly that size swell occurs.
The diagram implies that the dominant swell direction, shown by the biggest spokes, was S, whereas the the most common wind blows from the WNW. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Coastguards 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 graph. Because wind determines whether or not waves are surfable at Coastguards, you can load a different image that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. During a typical northern hemisphere winter, swells large enough to cause good for surfing waves at Coastguards run for about 43% 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.