Monday, June 10, 2013

SW12 + sun = 20

Last Sunday's wind forecast did not look great: computer models predicted 12 mph SW winds, the iWindsurf meteorologist a couple of hours of 12-16 mph, less the rest of the day. Here's what we got instead:
That's averages of 18 mph to 22 mph for most of the time from 4 pm to 7:30 pm, with gusts in the low to mid-20s. It was sunny, warm, and windy, but Kalmus was almost deserted - Elena was out early on her 7.5, and a few locals showed up, but most of the time, there where just 2 or 3 windsurfers on the water. What a waste of perfectly good wind! Here's a short GoPro / Clew-View video (available in HD on Vimeo):

I know some of my readers don't like math, but if you are a windsurfer in the Boston area, remember this little formula:
                                             SW 12 + sun = 20
If the forecast calls for SW wind around 12 mph and sun, it's quite likely that we'll see 18-20 mph winds in Kalmus - if the predicted air temperature for Cape Cod is about 10 degrees F warmer than the water temperature. Much larger differences, and we'll get decoupling - meaning very weak wind near shore, at least until the evening when things cool of and we may see 1 or two hours of great wind. If the water is as warm or warmer than the air, we will not get a sea breeze. But in spring and summer, there are plenty of days where the sea breeze makes for great sailing.

Two other local spots that also get nice sea breezes are West Dennis and Fogland. If the wind is more southerly (SSW or S), both West Dennis and Fogland are often better than Kalmus. West Dennis also seems just a little less prone to decoupling - if the temperature difference is 15 F, the wind in WD may be steadier. In rare SSE winds, Fogland is hard to beat on sunny days. But in SW winds and just the right temperature gradients, Kalmus will usually be windiest. If the wind is WSW, that almost certain, and the sea breeze boost may be substantially higher. I have seen plenty of days where the forecast was for 15 or 20 mph WSW, but the actual wind was 30 or 35.

To check the current water temperatures, you can look at the Nantucket Sound buoy readings; the observations for Woods Hole; and the sea surface temperature graphs at Rutgers University.

1 comment:

  1. I was at Ned's Point starting at 2:30. Wind was about 20 knots. No one else showed up.

    Based on the wind at home in the morning, I thought there was a chance and kept looking at the readings.