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Windfind- Arrroyo Laguna winds this week
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hitech



Joined: 13 Aug 2000
Posts: 75

PostPosted: Fri Sep 22, 2017 11:19 am    Post subject: Windfind- Arrroyo Laguna winds this week Reply with quote

Mike
As you work to understand the central coast winds, I thought You might be able to explain the winds the last couple of days at Arroyo Laguna. If you look at the 11am to 3pm time period on Wednesday and Thursday for Arroyo Laguna, you see wind speeds on the 15-20mph range and a fairly normal direction. However the reality was that we were sailing 5.2-4.2 and max powered on Wednesday and 3.8-4.7 max powered on Thursday. The winds were also a bit more side-off than usual with the strongest wind inside blowing the tops off the surf.
Was the true wind direction different than normal and Piedras Blancas was not picking up on the strong winds at Arroyo? There was definitely a disconnect between the two as Piedras Blancas normally would be a bit windier than the reality of Arroyo. Let us know what you think. Thx
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windfind



Joined: 18 Mar 1997
Posts: 1312

PostPosted: Fri Sep 22, 2017 3:38 pm    Post subject: Reply with quote

Hi hitech,

I am not remotely, yet, an expert on the Central California coast winds especially since you can count the times I have sailed Arroyo on one finger.

But in this case I can make a fairly useful analysis. Many sites along the coast such as Waddell, Piedras, Cabrillo. Leo etc have their winds slightly accelerated from a one sided venturi effect. This happens when the ocean winds compresses against the coastal hills or bluff and locally speeds up. Below are 2 video frames of a quick wind tunnel simulation frame I ran today that show this venturi effect.

In your case the venturi is most commonly focused near Piedras when the ocean wind is more WNW-NW which, as you can see in our archive data, image #1 is the most common Sept. winds at our Piedres sensor.

But on Thursday image #2 from our Piedras sensor and the San Martin buoy #3 and had winds more NW-NNW. (this occurs when the NPH extends a ridge into the Pacific Northwest.)

When this wind shift occurs the max venturi will move further south which probably caused the acceleration you noticed at Arroyo. And with the venturi weaker at Piedras the sensor would read low compared to the wind at Arroyo. If you look carefully at the time slot the previous evening (red diamond) you can see when this wind shift occurred.

The last two images also show this effect. Looking carefully at #4 you can see how the NW wind would focus a venturi at Piedras while more NNW winds #5 would focus it more to the south.

There are hundreds of such effects we have to learn before we can do really useful forecasts for a region. After 20+ years I am still learning lots of new things about such effects in the Bay Area.

It is not so much that I am a slow learner but rather that our wind pattens are changing from year to year compared to the norm 20-30 years ago.

Mike Godsey
iwindsurf.com/ikitesurf.com
Weatheflow.com



1 sided venturi.jpg
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1 sided venturi.jpg



Arroyo Laguna.jpg
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Arroyo Laguna.jpg


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hitech



Joined: 13 Aug 2000
Posts: 75

PostPosted: Fri Sep 22, 2017 6:27 pm    Post subject: Reply with quote

Mike
Thanks for taking the time and effort to look back and answer my question. It is the first time I have been there to see this effect but it could be more common than I know. It could also explain the typical Arroyo pattern where the winds ramp up around 130pm and the wind direction on the water changes from side-on to side shore/side-off (but not a radically as Thurs/Fri). I would guess the Venturi would be shifting from Piedras south to Arroyo although normally the wind speed differential would not be as radical as the last couple of days.
Hopefully this can help to get you more comfortable with forecasting Arroyo Laguna.
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nw30



Joined: 21 Dec 2008
Posts: 4056
Location: The eye of the universe, Cen. Cal. coast

PostPosted: Sat Sep 23, 2017 12:34 pm    Post subject: Reply with quote

I'm there just about everyday it blows, and I live only 10 minutes away, this week was pretty awesome (if you don't count the swell size), 4.2 for me 4 days in a row, but I have adopted a rule for myself. I can see the ocean in an upwind direction from my house, so you'd think that I have a pretty good handle on what it's doing up there at any given time, but it's not as accurate as it would seem. Even when taking the short drive up there, looking at the ocean on my way up, only gives me indications, but not guarantees. It's only when I drive over that last hill between San Simeon cove and Arroyo do I really know what it's doing.
It's all topography, the coastal hills and the curvature of the shoreline, which creates a micro condition that can sometimes be different from all the other indicators.
It can work both ways, awesome indicators on the way up, only to find Arroyo in a wind shadow, or crap indicators on the way up only to find Arroyo ripping.
Odds though are generally in your favor if you are paying attention to forecasts and reports, I prefer the Piedras reports more than the San Martin bouy reports, but some of my local friends prefer the other way around. We all have our reasons.
Was this any help? Probably not.

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windward1



Joined: 18 Jun 2000
Posts: 994

PostPosted: Sat Sep 23, 2017 12:43 pm    Post subject: Reply with quote

nw30,

Sounds like you are saying that you have to go, to know.
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nw30



Joined: 21 Dec 2008
Posts: 4056
Location: The eye of the universe, Cen. Cal. coast

PostPosted: Sat Sep 23, 2017 12:48 pm    Post subject: Reply with quote

For a guarantee, yes, but I go quite often, and get wet most often, but I always take my full quiver of boards and sails, always, 3.7 to 5.7, some take 3.5 to 6.2. It's best not to leave anything at home, especially beer, and some here may know who I'm talking to.
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hitech



Joined: 13 Aug 2000
Posts: 75

PostPosted: Sat Sep 23, 2017 7:10 pm    Post subject: Reply with quote

NW30
In your experience, how far into the Fall do you usually get to sail at Arroyo? I've been is told that they typically end before now but they remain solid this year.
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nw30



Joined: 21 Dec 2008
Posts: 4056
Location: The eye of the universe, Cen. Cal. coast

PostPosted: Sun Sep 24, 2017 11:25 am    Post subject: Reply with quote

Hopefully we will have a good what we call "the second season", which usually starts just before or at the beginning of fall, which is why last week's wind wasn't really a surprise. The wind often backs off a bit during July and August, and returns stronger in Sept., and can last up to around Thanksgiving which is the traditional end of the season. Sometimes, depending on conditions, the Santa Ana winds in S. Ca., (typical in the fall) are fed by the northwest winds in this area. General season, Easter to Thanksgiving.

If lucky, it's happened several times, you can get a great session in on T-day. There is nothing like returning home to a T-day dinner after windsurfing, assuming your assistance wasn't required for meal prep before hand, then it can become an issue, I've experienced that also. Confused

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MCDORO



Joined: 15 Nov 1993
Posts: 58

PostPosted: Sun Sep 24, 2017 10:48 pm    Post subject: Reply with quote

If you view Arroyo on any simple map, and someone asked you what kind of wind you might find in that area in the summer, knowing the prevailing wind is from the North-North-West, I think the most common answer would be an eddy type of wind...looks like it could be a relatively calm area in that stretch from Pidras South to San Simeon. Aint, though...They have docents now? Gate? Haven't been there in couple of years..time goes by.
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verendia



Joined: 20 Oct 2013
Posts: 5

PostPosted: Tue Oct 17, 2017 8:13 am    Post subject: Reply with quote

Can anyone tell me how AL is on a north swell. Thanks in advance
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