Friday, March 3, 2017

Weather Windows, Whether Windows

As predicted, we are sitting in a windy anchorage in Melbourne, Florida - because, as predicted, a weather front brought northeast winds of 20 knots, gusting higher and expected to be even higher tonight. But, we are in a good place. We are tucked behind the Melbourne Causeway so we get a lot of breeze but the waves are small, if a little choppy. It is really a good combination for us at anchor. The wind cools us off and keeps our wind generator humming along. It has been sunny, so the solar panels are doing their thing, as well. We have, in fact, been making electricity all day instead of draining the batteries sitting here. Gotta love free energy.

Anchored south of the Melbourne Causeway. Boat ramp
is just out of frame to the right.

There is a small boat ramp along the causeway that is perfect for taking Tilly to shore. A walkway along the causeway goes all the way to the ocean. We walked over there this morning and got pizza from Bizarros for lunch. The ocean is whipped up nicely by the wind but, due to the sunny conditions, it is shining and colorful. Not a bad place to wait for a weather window.

We spend a lot of time talking about weather windows, I guess. It is a favorite topic among cruisers - especially when they are stuck somewhere because they don't have a window. Our friend Jack asked for some clarification on what, exactly, we are waiting for, weatherwise, to cross the Gulf Stream to the Bahamas. So, Jack, here it goes.

Deciding whether a weather window is acceptable is like any good decision process. You feed it basic parameters, process the current variables and then see if the answer falls into a viable range.

  • We calculate our rate of travel on SeaClearly to be 5 to 5.5 knots. We often make better time but this is a good average. So, if we need to make 120 nautical miles, we need between 20 and 24 hours of acceptable travel conditions.

  • We also have a range of wind and wave conditions that we are willing to endure. Sailing or motoring stops being fun when waves are 4 to 5 feet on your nose, 6 - 7 feet on your beam or 8 feet from behind. You can travel in more (and we have) but we don't want to start off expecting worse than that. It will get worse on its own.

  • Wind is usually directly proportional to the waves. Anything above 10 on your nose is bashing. Thirteen to about twenty knots (not on the nose) is our sweet spot for sailing. Twenty - twenty five from the stern can be surprisingly comfortable unless the waves are from a different direction.

  • The normal Tradewinds coming across the Caribbean blow from the east constantly. On a fairly regular basis, the weather fronts coming across the U.S. dampen the east winds long enough for slow boats like us to jump across the Gulf Stream. For the past 2 months, the fronts have passed so quickly that the crossing conditions only lasted for 12 - 18 hours.

Current Gulf Stream position and currents. This picture
doesn't tell the story of the current weather - which
is absolutely atrocious.
  • The Gulf Stream is, as they say, a huge river that runs through the ocean. The volume of water that  moves north out of the Gulf of Mexico and up the east coast of the U.S. is astounding. The current flow varies, averaging 2 - 2.5 knots but can be as high as 7 knots. The stream is around 20 miles wide with wider parts, eddies and branches spinning off. When the wind comes from the north and hits the opposing current of the Gulf Stream from the south, the result is a washing machine. It creates its own weather with huge, steep waves, local squalls with high winds and, generally, nasty conditions. This is one of those weeks. The northeast winds that we are sitting in here at Melbourne have tossed the Gulf Stream into a frenzy of 30 - 40 foot waves with 35 - 45 knot winds - well outside our window. Outside most people's window.

  • Then, of course, there are tides. Especially leaving the east coast inlets, you need to ride the tide out. If you start off by bucking an incoming tide you will be off to a very slow beginning. And, while possible to leave in the dark and arrive in the dark, daylight is best for both. Traveling at night is not so bad.

So, if we intend to leave Fort Pierce, Florida to go to Green Turtle Cay in the Abacos, Bahamas (our current target, around 180 nautical miles) a weather window, for us, means winds have dropped to between 10 and 15 knots from somewhere south - preferably southwest but we will take south or southeast if not too high. The forecast has to call for conditions that remain steady or get even lighter for 24 to 36 hours. Squalls need to be minimal or non-existent. The Gulf Stream needs to have had time to settle back down from the last round of north winds. And we need to have the Tradewinds stalled long enough to get us safely into our destination before we get hit in the face with east winds again. We want to leave at daylight on an outgoing tide and be across the Gulf Stream and onto the Bahama Banks by nightfall, arriving someplace the following morning.

That's what keeps us up studying charts at night and listening to Chris Parker, our weather guy, in the morning. We have hoped for a long enough weather window since Day One of our trip this year. I think we may have tried going directly from Charleston, Port Royal, St Marys or St Augustine if the circumstances had presented themselves. Instead, we have slowly worked our way south. With each move, the required window gets shorter as we get closer. Hopefully, this next one, on Wednesday, will be the ticket to Paradise!


  1. Predictably excellent explanation of what goes into your decision process - very informative for us landlubbers! It's fun to be reading your blogs again. Best wishes for an uneventful crossing, and soon.

  2. Randy! Thanks for checking on us. I fell out of the habit of writing stuff down but I am going to try to be more consistent with my posts. Great to hear from you.