The rose diagram shows only the swells directed at Sprecklesville that coincided with light winds or offshore conditions over a normal December. It is based on 1736 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. Green and yellow represent increasing swell sizes and red shows biggest swells greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how frequently that size swell happens.
The diagram suggests that the prevailing swell direction, shown by the biggest spokes, was N, whereas the the prevailing wind blows from the E. The chart at the bottom shows the same thing but without direction information. For example, swells larger than 1.5 feet (0.5m) coincided with good wind conditions 16% of the time, equivalent to 5 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal December but 7% of the time we expect swell in the range 2-3m (6.5-10ft) 7%, equivalent to (2 days). Taking into account the fraction of these swells that coincided with expected offshore winds, and given the fact that Sprecklesville is exposed to open water swells, we estimate that clean surf can be found at Sprecklesville about 16% of the time and that surf is messed up by onshore wind 43% of the time. This is means that we expect 18 days with waves in a typical December, of which 5 days should be surfable.
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.