West Coast Wind Blog: Part 1, 3rd. Ave’s shifting battle lines…

WSW and WNW winds converge making for unreliable wind near launch site.

by Mike Godsey, Mike AT iwindsurf.com

Here are some of the e-mails I received from customers about the winds INSIDE at 3rd. Ave. & Coyote yesterday Aug. 31, 2018 versus the windgraph:

R,
“Reading your report this morning, yesterday was indeed a super weird day. We had NW winds inside at Coyote (with some fluttering SW gusts), with up and down (sometime strong) W to SW winds halfway towards the channel. I have sailed here for 15+ years. Is it me, or is this frequent eddy thing a new phenomenon? Every time I feel like we have a good tide set up for some fun, our friend eddy shows up and ruins the party. Smile

C,
“10m kite twin tip board. 4:50pm to 6:20pm.
Struggle the whole time. Up and down wind. Lots of down wind low teens even times when hard to keep the kite flying. And many up times soild mid 20s even a little over powered. I hung in there but it was really a constant struggle. Also had a significant westerly component! I was not alone I discovered after taking to other kiters about the conditions. Thanks for listening!”

K,
“4:00 wind was NW, filled in to the shore
4:30 wind had turned W, light at the shore. I had to work hard to keep the kite up getting through the golf course wind shadow at the lower beach.
4:30-5:00 wind was light and gusty
5:30 wind got strong and weak in streaks
We kept crossing from strong to weak to strong.”

So what the hell is going on! For many years 3rd. was one of the most reliable sites in the Bay Area but in recent years and especially this year the winds have often been weird especially inside. It has taken me a very long time to figure out what is going on and it is still a challenge to forecast the issues in advance.

Basically, there are 2 different issues that can spoil the 3rd. and sometimes Coyote winds inside:

1. The increasing frequency of counter-clockwise spinning eddies off the Golden Gate ccreating  strong wind in the Hwy. 92 gap.

2. The times that the pressure gradient from San Bruno Gap to Morgan Hill to Pacheco Pass to the Central Valley is much weaker than the gradient from the San Bruno Gap to the Altamont Pass which favors less reliable W. wind rather than WNW wind.

Part one of this blog covers this first factor:

Find the 3rd. Ave. launch sites area. Then notice the solid WNW winds coming through the San Bruno Gap towards the channel.

Now notice the W to WSW eddy winds near Half Moon Bay that are funneling through the Hwy. 92 gap area.

Notice how the WNW winds and the WSW winds converge and the battle near the launch sites. Yesterday this battle occurred near the launch area hence the reports above.

But on some days this battle line may be a mile inland which would mean great winds inside and outside at 3rd.

At this time I am pretty good forecasting which days are likely to have such a battle and mention this in the text, bullets and table text. But I still cannot forecast exactly where the battleline will be.

Worse, as K. above discusses, the WNW vs. WSW battle line can move around during the afternoon. So if you arrive at the right time you are praising the forecast, the wrong time you are cursing! And Coyote, often on the edge of the battle is even harder to forecast during eddy conditions. While Palo Alto and Natural Bridges and San Luis benefit from the eddy.

For example yesterday I incorrectly thought the battle would be a bit inland of 3rd. and forecast good winds inside but gave lots of warnings about eddy issues. And tomorrow I am pretty certain the eddy will win.

Keep sending or posting reports. I love criticism but reports are more likely to lead to improved forecasts.