Arpoador Swell Statistics, Setembro: Surf with Light or Offshore Winds
This image shows only the swells directed at Arpoador that coincided with light winds or offshore conditions through a typical September and is based upon 2400 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 illustrate increasing swell sizes and red represents the biggest swells, greater than >3m (>10ft). In each graph, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the most common swell direction, shown by the longest spokes, was SE, 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 31% of the time, equivalent to 9 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal September but 8% of the time we expect swell in the range 2-3m (6.5-10ft) 8%, equivalent to (2 days). Taking into account the proportion of these swells that coincided with expected offshore winds, and given the fact that Arpoador is slightly protected from open water swells, we calculate that clean surf can be found at Arpoador about 31% of the time and that surf is messed up by onshore wind 23% of the time. This is means that we expect 16 days with waves in a typical September, of which 9 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.