Tuesday, November 6, 2012

Too Much Wind?

It's beautiful and sunny, if a tad chilly, today on Cape Cod, but this will change tomorrow. Clouds and then rain will come; temperatures will rise a bit, but it will feel colder because it will be very windy. Here's what on computer model predicts:
Winds of about 50 MPH, gusts up to 60 mph - that's would be enough for the professional storm chasers, but it's too much for regular windsurfers. Fortunately, other computer models predict a bit less:
Winds "only" in the high 30s, with gusts below 50 until 1 pm - I have sailed in similar conditions. But which prediction will be closer to the truth?

The first chart if the GFS model for Chapin on Cape Cod; the second chart the NAM model for Duxbury. The NAM model has a higher resolution, and is often more accurate - but for Duxbury in the fall, if often under-predicts the wind. I think the actual wind will come in somewhere in between the two charts, perhaps like the NAM model for Chapin predicts:
To be clear - I have no intention to sail at Chapin, I am just using the forecast because in the past, the Chapin forecast has often predicted winds in Duxbury Bay quite well.

With the winds coming from the northeast, it will be chilly (mid-40s F, about 7 C) and cloudy. So why am I thinking about going sailing? Well, for one thing, the water is still relatively warm (above 50 F / 10 C). Then, the predicted NE wind direction is ideal for Duxbury Bay, which is protected by a large sand bar. At high tide, NE winds in the 30s still can create a lot of chop in the bay, and make sailing very challenging. During a similar storm last year, two of our local speed surfers who both sail orders of magnitude better than I went out, but neither got any speed they deemed worth posting. But tomorrow morning, the tides will line up just right:

Low tide will be at 11:17 am, with a water level of +1.79 feet. At a normal low tide ( 0 feet), Duxbury bay becomes unsailable, because the water levels are too low; but at +1.8 ft, most of the bay will have water deep enough for windsurfing - here's the depth chart:
Green areas can be dry at a normal low tide, and might be too low for sailing tomorrow. But in the blue areas, the water depth between 9:50 am and 12:50 pm will be mostly between 3 and 5 feet - taller windsurfers should be able to touch ground at most spots. When we recently sailed Duxbury Bay in 25-30 mph winds, the water got very flat as we approached low tide; unfortunately, we had to stop about 2 hours before low tide, when the water levels dropped below 2 feet (that day, low tide was slightly negative). Tomorrow, however, should a perfect setup of strong and increasing winds and sailable low tide.

If you think about joining us tomorrow in Duxbury, there are a number of things to remember:

  • Boots are an absolute must when sailing Duxbury Bay. There are lots of sharp shells on the ground that will cut your feet if you try to sail barefoot.
  • Helmets are definitely a good idea, if not a must, in the expected 40+ mph winds. 
  • Bring warm gloves or mittens! Open-palm gloves should be warm enough.
  • The wind may come in stronger than the models predict, and/or increase faster. Even at low water levels, walking through the muck to get back may be very difficult.
  • The dept chart shown above is a few years old, and water depth may have changed. There are rocks in the water, so there is a chance of very sudden stops from hitting something! Also, there may be piles of reeds in the water that can stop you dead. Two more reasons to wear a helmet..
  • The tide may come in higher or lower than forecast. During the last storm, tides at other places were about 2 feet higher than predicted because the wind was pushing the water towards shore. This might happen in Duxbury Bay, too!
  • The harbor master may tell you that you cannot windsurf. He takes his job seriously, and will generally not let you go sail in really strong winds if you are alone. However, he has let two of us (Nina and me) sail in 35+ mph winds before after checking that there were at least 2 windsurfers going out. We hope to be there tomorrow morning before 10 am, but if the wind comes in even stronger than forecast, we may cancel.
  • If you have never sailed in 35+ mph winds and 45+ mph gusts, I suggest that you wait for a warmer day. Sailing in winds this strong is dangerous!
For those who go out tomorrow, it will be a day to remember. I still have vivid images in my head from an overpowered 3.7 day in Tarifa 30 years ago! We hope to sail our smallest sails (3.4 for Nina) and boards (the F2 Missile will come along), and if it's flat enough, personal speed records will be broken.

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