Crazy monsoonal squall

[BRIMAR]

So now I know what it's like to be waterboarded! For those who can interpret this graph you can see how the wind was really great right up until it wasn't. I was in the channel a mile and a half out when the wind started dying. I sensed this and headed for land I was able to stay on my board 1/2 the way but alas it died completely with nearly a mile to shore. I swam for 20 minutes till I could walk along the bottom of the bay on my tippy toes. I was half swimming half walking in neck deep water for the next HOUR! Since it had been so windy the water was still super choppy and with every swell I was waterboarded! Fortunately the water was warm and I got to watch a great sunset from the bay.

[windfind]

Hi BRIMAR,

Can I use your text in my blog about monsoonal conditions?

Mike Godsey
iwindsurf.com

[jse]

This actually happened to me a few years ago near Marin Islands off of Rod and Gun. Set out in a shorty on a typical building NW'erly afternoon. When I got to the boat channel the wind all but died. I had to swim / slog / tip-toe walk for the next 2 hours. At one time I caught a puff from the east! Sailed a ways back to the launch on a port tack.

Steve

[gerritt]

Hey Brian. Glad to see you are alive. You were about 200 yards behind me and then you went down and I didn't see you. I bobbed in and made it to the ramp. There was a woman on shore considering calling 911, the coast guard, etc. You were one of 3 still out. We watched until the other two got in and you were in close enough that we knew you would make it. I'm not sure if emergency services bills for rescues, but you didn't need rescuing, just time and patience. It was fun - until it wasn't.

[isobars]

This is pretty common if the wind is caused by the squall rather than by larger-scale gradients. I'm sure windfind can explain it mo bettah, but here's my attempt borne of decades of sailing squalls and full-fledged thunderstorms.

The squall's downdraft creates a local dome of high pressure directly inside/beneath that downdraft. That, and the fact that that vertical wind hitting the earth's surface must now go somewhere and its only choice is sideways, produces wind which spreads radially across the surface, usually strongest in the storm's/squall's path. (Such microbursts can hit 150 mph if the storm is intense enough.) But once the leading edge of this downdraft and its pressure dome -- the eye of this non-rotational surface storm/squall -- reaches a given spot on the surface, that radial wind shuts off.

FORTUNATELY, the leading edge of the rainfall often precedes the calm eye by a minute or two. Thus when I'm sailing in squall- or storm-generated wind, I sprint for shore the first time I even THINK I feel a raindrop. Sometimes I sail home, sometimes I swim.

Even if the winds are synoptic (i.e. caused by regional gradient rather than the squall's downdraft), a squall can shut the wind off and/or change its direction by 90 degrees within well under a minute. This happens quite frequently in the eastern Gorge deserts, stranding a few or even a couple of dozen inattentive sailors on the river for up to hours when strong and steady westerly winds switch to dead offshore at 5-15 mph.

We were sailing squall-boosted winds at the Hatchery, and when that first raindrop hit it was too late. At least 20 of us got caught in mid-jump and had to wait 'til the wind picked up again to even come down. We finally swam to shore at Cheap Beach or Swell. [Only one sentence of that is untrue.]

[naylor]

It looks like it picked up again to at least sloggable conditions not long after.
But this is why my smallest board is still floaty enough for me to slog in on even in 2 kts of wind, and why I will never take up kiting!

[BRIMAR]

Go ahead Mike.
Truth is I had a strong feeling it would die fast as it built so fast. As an airline pilot I have studied microbursts pretty extensively and seen them from the sky and the ground.
this was not a microburst.
There was a Bazar rolling cloud over the Hayward area that I think was responsible for the 45 minutes of 25-32 we enjoyed.
It was not a cloud of vertical development but something else. Additionally Coyote had the same phenomenon.
Thanks Gerrit I as much as I wanted help I'm glad they didn't call the CG.

[isobars]

[windfind]

Hi BRIMAR,

Thanks for the permission! Here is the monsoonal blog along with your story:

http://blog.weatherflow.com/bay-area-wind-blog-wth-is-monsoonal-moisture/

Isobars explanation is pretty accurate for a squall or thunderstorm that is moving very slowly or is stationary.

It gets complicated if the squall is being drive by a larger scale wind mass like the trade winds in Maui. In that case as the squall approaches you will feel an abrupt and major increase in wind velocity. Then as the squall passes over you the winds fade and then on the back side of the squall the winds fade abruptly since the outflowing wind from the squall is now going against the direction of the larger scale winds and they partially cancel out.

So if you have an overall steady wind flow beyond the perimeter of the squall you just bob around until the squall has totally passed and the winds will pick up again. This works fine in the morning to late mid afternoon but if you are caught in a squall in the late afternoon the prevailing wind may die before the squall departs.

I once got blasted by 30 knots winds on a 5.2 and then bobbed around outside Ho’okipa for an hour at the start of a downwinder to Kanaha. It gave me the incentive to learn more about the meteorology of squalls.

Now when I forecast for transpacific yacht races and I see a North Pacific High's movement is going to bring it in contact with moist air I forecast a squally pattern for the race. And if the boat is exceptionally fast I suggest that they plan on playing the squalls by tacking often to stay in the squalls outflow windy zone.

Mike Godsey
iwindsurf.com