Llangennith Swell Statistics, Autumn: All Swell – Any Wind
This image shows the range of swells directed at Llangennith through a typical northern hemisphere autumn, based on 5829 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 Llangennith, and at Llangennith the best grid node is 17 km away (11 miles).
The rose diagram illustrates the distribution of swell sizes and swell direction, 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 happened only 16% of the time. Green and yellow show increasing swell sizes and biggest swells greater than >3m (>10ft) are shown in red. In either graph, the area of any colour is proportional to how often that size swell happens.
The diagram indicates that the dominant swell direction, shown by the biggest spokes, was WSW, whereas the the prevailing wind blows from the SW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Llangennith and offshore. We combine these with the no surf category of the bar chart. To keep it simple we don't show these in the rose diagram. Because wind determines whether or not waves are clean enough to surf at Llangennith, you can select a similar diagram 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 surfable 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.