Which way will the wind blow?

July 31, 2020 in Passage planning - 1 Comment

Based on the current forecast, Tim and I are planning to shove off from Harbor Island in San Diego for Catalina Harbor on Catalina Island at 1800 (ahem, 6:00pm) on Saturday. It’s about 95 nautical miles (NM) if you can go in a straight line.

Usually you can’t sail straight northwest from San Diego because that is almost always where the wind is coming from. [Note to landlubbers: Sailboats can’t sail straight into the wind, we have to be at least 30 degrees off the wind–kind of at 10 o’clock and 2 o’clock if the wind direction is 12 on a clock).] If this predominant wind direction were what we were seeing, we were anticipating a 30-36 hour trip.

Good news, though! This weekend’s forecast has the wind coming out of the south, so we can go in almost a straight line! You will hear us mention over an over that, “things just work out for Tim.” And this trip seems to be abiding by this cosmic rule.

But, here’s the kicker… one weather model, the ECMWF (European) model has a more favorable forecast than the GFS (American) model. Let’s take a look…

Leaving San Diego 1800

Look in the bottom right corner of each image. That’s about where we’ll be at 1800. ECMWF has the wind already backed around from the south at 8 knots. We like to see anything from 8-20 knots (kt), so that looks pretty good. GFS, however, still has the wind coming from the west at 6 knots.

Now, from the west is not terrible, but 6 is a little light–especially at the end of the day because the wind typically dies in the evening in Southern California. Let’s see what happens in five hours…

Outside of San Diego harbor 2300

ECMWF has the wind backing even more to the southeast (which is perfect). And, 7 kt of windspeed is not awesome, but also not bad–especially for the middle of the night. Hurray for the European model and the wind forgetting that it’s in Southern California! But look at the dreadful American model. Still south and a miserable 2 kts.

A little less than half way 0400

And now at 0400 you can see why they American model has the wind speed so light. It has the center of the low (that big blue blob sitting over Catalina Island in the upper left). Think of the center of a low kind of like the eye of a hurricane (don’t worry, that is NOT a hurricane!). It’s very calm because a coriolis force deflects the surface wind slightly away from the center in a counter clockwise direction.

In the European model, the low (the blue blob) is more south and west over San Clemente Island, and is just kicking that wind around the center of the low. Which, in this case works to our benefit given where we think we’ll be at 0400. And look at that beautiful 10 kt prediction from the southeast. This model has it shaping up to be a beautiful sunrise sail!

Three quarters of the way there 0900

Yea European model. Boo American model.

Almost to Catalina Harbor 1200

If our average boat speed is 5-6 knots, then we think we’ll get to Catalina Harbor around 1200 on Sunday. Which is good because here are our goals (beyond the obvious–arrive in one piece): 1) don’t arrive in the dark and 2) don’t get there too late so that we don’t get a mooring ball.

If the ECMWF model holds true, we’ll set our sails, point our bow toward Catalina and have a very lovely sail. If the GFS model ends up being the more accurate of the two, we’re going to use a lot of fuel and give our Yanmar a good workout (and Tim will likely be pretty darn grumpy).

So why are we putting our stock in the European model? Well, first, confirmation bias. It shows us what we want to see, so of course we like it better! Seriously, though, the European model has historically performed better. So, we’ll hopefully snack on our baguettes and sip our cappuccinos all the way to Catalina.

Watch us on Instagram @gntsailing to see which way the wind blows!

Au revoir. Addio.


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1 Comment

  • Susie Buzan August 5, 2020 at 3:54 am

    I see now what you have been learning for the last 8 or so years. Looks like you got it!

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