The rose diagram illustrates how commonly and how strongly the wind blows from different directions through a typical August. The biggest spokes point in the directions the wind most commonly blows from and the shade of blue implies the strength, with deep blue showing the strongest winds. It is based on 1736 NWW3 forecasts of wind since since 2006, at 3hr intervals, for the closest NWW3 model node to San Mateo, located 20 km away (12 miles). There are too few recording stations world wide to use actual wind data. Without question some coastal places have very localized wind effects that would not be predicted by NWW3.
According to the model, the most common wind at San Mateo blows from the N. If the rose plot shows a nearly round shape, it means there is no strong bias in wind direction at San Mateo. On the other hand, dominant spokes represent favoured directions, and the more deep blue, the stronger the wind. Spokes point in the direction the wind blows from. Over an average August, the model suggests that winds are light enough for the sea to be glassy (the lightest shade of blue) about 0% of the time (0 days each August) and blows offshore just 0% of the time (0 days in an average August). In a typical August winds exceeding >40kph (25mph) are not expected, but 0 have winds on the range 30-40 (19-25) at San Mateo
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.