Llangennith Swell Statistics, April: All Swell – Any Wind
This picture shows the combination of swells directed at Llangennith through a typical April, based on 1680 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. In the case of 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 illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These were forecast 31% of the time. Green and yellow illustrate increasing swell sizes and red illustrates the biggest swells, greater than >3m (>10ft). In either graph, the area of any colour is proportional to how often that size swell was forecast.
The diagram indicates that the most common swell direction, shown by the longest spokes, was WSW, whereas the the prevailing wind blows from the NW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Llangennith and offshore. We group these with the no surf category of the bar chart. To avoid confusion we don't show these in the rose graph. Because wind determines whether or not waves are good for surfing at Llangennith, you can view an alternative image that shows only the swells that were expected to coincide with glassy or offshore wind conditions. Over an average April, swells large enough to cause clean enough to surf waves at Llangennith run for about 69% 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.