The rose diagram shows only the swells directed at Treasure Island that coincided with light winds or offshore conditions through a typical June and is based upon 1594 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 highest 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 was forecast.
The diagram indicates that the dominant swell direction, shown by the biggest spokes, was SSW, whereas the the dominant wind blows from the NNW. 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 11% of the time, equivalent to 3 days. Open sea swells exceeding >3m (>10ft) are unlikely to occur in a normal June but 11% of the time you can expect swell in the range 1.3-2m (4-6.5ft) 11%, equivalent to (3 days). Taking into account the proportion of these swells that coincided with expected offshore winds, and given the fact that Treasure Island is slightly protected from open water swells, we calculate that clean surf can be found at Treasure Island about 11% of the time and that surf is blown out by onshore wind 10% of the time. This is means that we expect 6 days with waves in a typical June, of which 3 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.