Friday, June 7, 2013

Don't believe the weather man!

I am a windsurfing addict with a job that allows me to go sailing anytime I want to, so I check the wind forecast and meter readings many times a day. Over time, patterns emerge from all this information; on occasion, that enables a better forecast than what the computer models and meteorologists provide.

Last weekend was a case-in-point. Computer models predicted similar SW winds from Friday to Sunday. The iWindsurf experts promised great wind on Saturday, but warned about decoupling on Sunday. But Saturday saw very little wind, except close to dusk, while Sunday had decent winds all day. No real surprise - Friday and Saturday were very hot, with inland temps in the 80s and air temps over the water in the low 60s. Perfect setup for decoupling, which is what we got. Only when the sun went down and temperatures started to fall did we get a bit of wind. Sunday was perhaps 5-10 degrees cooler, and the water had warmed up a few degrees, so the wind managed to stick to the surface. In Kalmus, it was still a bit up and down, but planeable all day. Dean managed to get a top speed of 33 knots, racking up almost 100 miles over the course of the day. He was still flying over the chop, with just the fin touching the water, when the tide came in and built up the famous Kalmus voodoo chop.

With the remnant of tropical storm Andrea passing over us tonight, the question is what tomorrow will bring. Maybe something like what Cape Hatteras is seeing today, with winds in the 30s all day? Or maybe almost nothing in the afternoon, as some computer models predict?
The screen shot above shows the prediction for tomorrow afternoon at 2 pm - low teens for Kalmus and most of the Cape. However, the shape looks a bit suspicious. Here's a similar graph from Windalert.com:
The colors are a bit different, but again, it looks like the wind will desperately try to avoid Cape Cod.

I'm sorry, but I think the stupid government computers have it wrong. Perhaps they think that wind hates land as much as government employees hate working on Friday afternoons? Fortunately, we also have a local wind prediction from a private company, Sailing Weather Service, that we can look at:
This looks more like it - WSW 20-22 knots (23-25 mph) very close to shore. Instead of the symetrical "land avoidance" in the first picture, the strong winds get very close to shore on the windward side, and are significantly stronger than on the leeward side. For tomorrow afternoon, my bet is on this model, and strong winds in the early afternoon. In WSW setups, we often see even stronger winds if Kalmus, probably due to some channeling and Lewis Bay right behind.

The winds will get weaker during the afternoon, but the timing of the drop is notoriously hard to predict. We might get wind all day, or it might drop rapidly at noon. The early bird will see the strongest winds, but may have to tolerate heavy rain. I plan check the radar maps and iWindsurf meter readings south of us to get an idea what's coming, and be at the water as soon as the rain stops. If you do the same, keep in mind that most meters in Rhode Island and Connecticut will show much less wind than we'll get on Cape Cod, with the possible exception of island and open water meters.

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