The sensor is located at Whitecrest Beach just to the south of the Whitecrest parking lot and beach access point. This is also the area used by paraglider and hang-glider pilots on NE to ESE days to take-off and soar the dunes between Highland Lighthouse in the north and Nauset Beach Lighthouse to the south.
Conditions at launch correlate best with the Gust values measured by the sensor. That’s the Red Line on the graph. Note that in some conditions (when it is flyable) the ‘average wind value’ can often be misleading.
When the onshore wind at launch (top/front of dune) is below approximately 12 knots, the sensor is usually in clear, laminar air and measures lulls (yellow line) in the true airflow. However, as the wind increases, the more the sensor is washed intermittently with rotor extending downwind from the lip of the dune. Lulls measured by the sensor in these conditions are NOT lulls in the true airflow and therefore can be misleading. This effectively lowers the average wind speed value. The gusts however ARE indicative of the true airflow and therefore correlate well with true conditions.
How far the rotor extends downwind is not only a function of wind speed, but also depends upon the angle of the wind in relation to the coastline and the properties of the air. Rotor will tend to be maximized when the flow is exactly perpendicular to the dune (ENE) and the air is less stable, such as on a buoyant late afternoon. Extent of rotor diminishes as the angle of the onshore flow with the coastline decreases. When the flow is alongshore, NNW or SSE, there is of course no rotor created and the sensor measures clean airflow. Rotor also diminishes as the air becomes more stable, such as on a cold February morning.
The true wind at take off (right on the lip of the dune) is also subjected to compression, the effect of which is lessened at the sensor. For this reason the Gust value + 12% appears to correlate well with the actual wind speed found at launch. Again, the effects of compression fluctuate with the angle of the wind in relation to the coastline and the properties of the air. The compression effect is less noticeable on less stable days, and more noticeable on more stable days.
As a rule of thumb:
Gust 10mph = Wind at launch 11.2mph
G 12mph = Launch 13.44mph
G 13mph = Launch 14.56mph
G 14 mph = Launch 15.68 mph
G 15 mph = Launch 16.8mph
G 16 mph = Launch 17.92mph
G 17 mph = Launch 19.04mph
G 18 mph = Launch 20.16mph
G 19 mph = Launch 21.28mph
G 20 mph = Launch 22.4mph
In alongshore and offshore winds, the sensor measures clean air, with no obstructions from any direction.
Also note that the Beachcomber Cam is extremely useful when used in conjunction with data from the sensor to determine conditions.