Llangennith Swell Statistics, April: All Swell – Any Wind
This image describes the variation of swells directed at Llangennith over a normal April. It is based on 2160 NWW3 model predictions since 2007 (values every 3 hours). The wave model does not forecast surf and wind right at the shore so we have chosen the optimum 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 describes the distribution of swell sizes and swell direction, while the graph at the bottom shows the same thing without direction information. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. These were forecast 29% of the time. Green and yellow show increasing swell sizes and red represents the highest swells, greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the dominant swell direction, shown by the biggest spokes, was WSW (which was the same as the dominant wind direction). Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Llangennith and out to sea. 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. During a typical April, swells large enough to cause good for surfing waves at Llangennith run for about 71% 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.