This picture illustrates how commonly and how strongly the wind blows from different directions through a typical northern hemisphere winter. The longest spokes point in the directions the wind most commonly blows from and the shade of blue implies the strength, with the strongest winds shown by the darkest shade of blue. It is based on 5047 NWW3 forecasts of wind since since 2006, at 3hr intervals, for the closest NWW3 model node to Porth Colmon, located 18 km away (11 miles). There are too few recording stations world wide to use actual wind data. Invevitably some coastal places have very localized wind effects that would not be predicted by NWW3.
According to the model, the dominant wind at Porth Colmon blows from the SW. If the rose diagram shows a close to circular outline, it means there is no strong bias in wind direction at Porth Colmon. On the other hand, dominant spokes show favoured directions, and the more the darkest shade of blue, the stronger the wind. Spokes point in the direction the wind blows from. Over an average northern hemisphere winter, the model suggests that winds are light enough for the sea to be glassy (light blue) about 6% of the time (5 days each northern hemisphere winter) and blows offshore 26% of the time (2 days in an average northern hemisphere winter). In a typical northern hemisphere winter winds stronger than >40kph (25mph) are expected on 11 days at Porth Colmon
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.