First the war stories then my analysis.
by Mike Godsey
Dmitry: “Madness increased beyond any measure as SFO shifted to 250degr and shot up to 39mph, but it became very bad on the water even 1hr before that.
Leonardo F.: “I was one of the unfortunate ones in the channel yesterday when it got weird. I experienced very gusty winds, and then suddenly it died, with my kite falling from the sky and messing with my lines. After ~15 mins the wind picked up again, very strong, I’d say 25+. I was charting my session yesterday, the red dot is when it all began. If you know the cause and/or can forecast this phenomenon, that would be terrific!”
Matt: “I was there- haven’t had a swim like that in at least 5 years. When it died it was sudden and complete, I’ve not experienced that before and hope never again. I was upwind a few hundred yards from the channel marker and there was zero sail pressure. Nada. I swam for about 10 minutes contemplating the building ebb, and then with a few light gusts from W-WSW I was able to waterstart and sail a bit, though pointed well S of the launch. It was up and down and I swam and slogged for another 20 minutes to get to shore, and then walked. By then the wind outside had come back up, but inside it was light to nothing. Observations- The early wind was canted more W- WNW, this is often the case when it comes up early. The lack of fog above the airport was unusual. In particular no building fog in the Hwy. 92 gap, which usually is the “head in now” signal when it starts flowing over and down the ridge. The wind was up and down and had holes, which is not unusual on an early W-WNW day. What was unusual was that more typically the holes still have some light NW wind, and the gusts are W. This time it was just holes w/o the NW content. So to me it was a classic SW shift, but it was extremely sudden and did not have the normal warning with fog in the 92 gap.”
T. Gautler: “I launched just seconds before the fade at third yesterday. As I was rigging on the beach at the upper launch I felt strong gusts and then big lulls. Then I launched my kite. It lulled twice the second time so hard my kite nearly flipped and crashed into the beach. Walking (running?) upwind about twenty feet fast and hard corrective action barely saved it.
A couple kite loops later and I was riding on the water. By this point I realized the wind was behaving rather erratically and I was probably in for a walk of shame. Everyone else’s kite dropped on the water. I continued to struggle with mine and kept looping it try to generate some speed. Every now and then I got a small puff of air that gave me some board speed. Finally my kite dropped near the main lower launch ‘pro channel’. Since I had just enough wind to fly the kite I decided to head back out to sea to see if I could make it upwind. Worst case was rocks anyway.
First tack brought me back to the same spot. The wind was strong in places and completely dead in others. I don’t know how to describe it, but even when the wind was strong it didn’t pull that hard on my kite. It felt like Swiss cheese. If I pulled in on the bar the kite would stop flying – it’s like the air was soft.
Finally by the time I got back to the upper beach the wind was just howling and I was pretty well overpowered and there were still these what I can only describe as violent lulls. A drop so hard my kite would nearly fall out of the sky and then a surge that would nearly yank me off my board. No beginner could have survived that. It reminded me of some gnarly 35+ days at Crissy on the inside.
I think I was the only one to ‘survive’ the drop. Everyone else went for a swim. That was probably the worst wind experience I’ve ever had in 4 years kiting at third.”
Brad S.: “The only reason i went out after the first wind die-off at 6pm, was that SFO was cranking at 35mph. So I gambled it would fill in, but instead went with plan B, which was practicing self rescue. I think all 4 kiters swam in…”
Carl: “Got out about 4;00 on 8m kite and the first blast that hit me almost had me going back for my 6m. The wind was much stronger way inside. When I got to the channel marker it started to pick up strong outside. I kited overpowered for about half an hour out there and it started to get gustier. As I came in, it got more and more holey with some gusts, and lulls to almost nothing. I ended up swimming. When I got in, my brother was on shore with his windsurfer rigged with 4.7. At around 5:45 he slogged out to the wind line and sailed happily overpowered on the outside until 7:15 or so and planned all the way back in.
I don’t forecast on Wednesday but if I am not on the water I normally follow the Bay Area wind anyway. I knew something had gone wrong when my iphone received this message from Ben Miller who was on duty:
I know why Berkeley was bad today. In fact, WRAMS modeled it perfectly. However, why is 3rd Ave Channel so bad when SFO is 35 gusting to 45 and Coyote is ripping at 30?
Since I knew Ben was swamped pumping out forecasts I decided to see if I could find the answer.
My first step, as always, was to get insights from those of you who were on the water. Data is great but onsite reports are invaluable.
All of you Peninsula regulars know that if there is even a hint of SW flow near the Peninsula Coyote and 3rd. Ave. become unreliable especially inside. Usually the first hint of SW flow is a massing of clouds over the coast range to the west and if you see fog moving towards the launches from the Hwy. 92 gap to Half Moon Bay savvy kiters and windsurfers head to shore to avoid a swim. But yesterday there were no hints of SW surface flow and only traces of marine layer clouds along the coast. So even the sharpest of locals had to swim.
Yesterday there was very strong NW surface wind from the North Pacific High. As that wind poured through the San Bruno Gap it was torn between turning more westerly towards the Altamont Pass or continuing on its NW trajectory. Nothing new here and Coyote and 3rd. Ave. people are used to that those shifts. But yesterday the NW surface wind was being augmented by very strong NW wind just aloft so it was Gusty… but nothing new here either. But what was different were the strong WSW to SW gusts also just aloft. When those southerly winds stirred the surface winds 0ver Coyote and 3rd. Ave. 2 things would happen.
1, Kites and sails would suddenly lose their power as the NW wind both at the surface and aloft was pushed away creating huge holes
2. When the WSW wind left the surface both the surface NW wind and the NW wind aloft would suddenly shoot into the area creating huge blasts.
Since 1 and 2 were happening in random patches over the waters you would see distinct glassy areas while nearby there would be white caps. For a windsurfer you would have the weird sensation of seeing white caps around you but no power in your sail. For a kite up in these winds it would be more dramatic with the kite falling out of the air or being vastly overpowered. The images below illustrate some of this.
Bottom line: On days when we see Strong NW winds and Strong southerly wind aloft we will issue “Swim Alerts”