The rose diagram shows only the swells directed at Steamer Lane-The Slot that coincided with light winds or offshore conditions over a normal northern hemisphere summer and is based upon 5066 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 show 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 frequently that size swell happens.

The diagram suggests that the most common swell direction, shown by the biggest spokes, was WNW (which was the same as the dominant wind direction). 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 9% of the time, equivalent to 8 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal northern hemisphere summer but 3% of the time we expect swell in the range 2-3m (6.5-10ft) 3%, equivalent to (3 days). Taking into account the fraction of these swells that coincided with expected offshore winds, and given the fact that Steamer Lane-The Slot is slightly protected from open water swells, we estimate that clean surf can be found at Steamer Lane-The Slot about 9% of the time and that surf is messed up by onshore wind 56% of the time. This is means that we expect 59 days with waves in a typical northern hemisphere summer, of which 8 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.