The rose diagram shows only the swells directed at Praa Sands that coincided with light winds or offshore conditions through a typical March and is based upon 1724 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 represents the largest swells, greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how often that size swell happens.
The diagram indicates that the prevailing swell direction, shown by the biggest spokes, was WSW, whereas the the most common wind blows from the NW. 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 8% of the time, equivalent to 2 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal March. Taking into account the proportion of these swells that coincided with expected offshore winds, and given the fact that Praa Sands is exposed to open water swells, we calculate that clean surf can be found at Praa Sands about 8% of the time and that surf is messed up by onshore wind 17% of the time. This is means that we expect 8 days with waves in a typical March, of which 2 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.