Llangennith Swell Statistics, Autumn: All Swell – Any Wind
The graph describes the combination of swells directed at Llangennith through a typical northern hemisphere autumn, based on 6516 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the coastline so we have chosen the best grid node based on what we know about Llangennith, and at Llangennith the best grid node is 17 km away (11 miles).
The rose diagram illustrates the distribution of swell sizes and directions, while the graph at the bottom shows the same thing but without direction information. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. These happened 16% of the time. Green and yellow represent increasing swell sizes and red shows highest swells greater than >3m (>10ft). In either graph, 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 biggest spokes, was WSW, whereas the the dominant wind blows from the SW. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Llangennith and away from the coast. We group 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 Llangennith, you can load a different image that shows only the swells that were expected to coincide with glassy or offshore wind conditions. Over an average northern hemisphere autumn, swells large enough to cause good for surfing waves at Llangennith run for about 84% 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.