West Coast Wind Blog: Stinson Beach baby steps!

How we do a “Guesscast” for Stinson Beach while taking baby steps up the forecast learning curve.



by Mike Godsey, Mike AT iwindsurf.com

The banner above is from a Coast Guard helicopter scouting trip Rob and I took looking for possible weatherflow.com sensor sites.

We have just started doing daily forecasts for Stinson Beach in Marin County. Based upon past experience it will take 3-4 years for the forecast to become useful. So you might want to stop reading now and come back in 2021.

Why? It is a long slow beautiful drive to Stinson and getting skunked by a crap forecast or needing a rescue because of unforecast sudden mid-afternoon fluky offshore winds is not fun. And far worse would be having your “kook” ineptitude in the surf or beach destroying the local’s access to their limited launch site.

So this blog is mostly aimed at experienced kiters willing to pay their dues by driving to Stinson without kiting and just watching and talking to locals a few times until you, and they, are confident you know the local rules.

Stinson will  be an especially hard place to forecast accurately despite the fact that I once lived and surfed in nearby Bolinas. Why so difficult? Because Stinson is a convergence zone for many different  winds including:

  • NW from the North Pacific High curving around Duxbury Pt. to Stinson as W. wind
  • NW funneling between Bolinas’s big and little mesas.
  • NW wind funneling just above the trees in the Olema Valley from Stinson.
  • Uncommon W. wind from the North Pacific High
  • SE winds from a Golden Gate Eddy.
  • A very local thermal wind as the slopes of the coast range clear of fog and create a local banana belt low pressure that may cause the aforementioned wind curve into Stinson.

And on many days you  have a combo of those winds that can make Stinson build or fade or go offshore in a moment. For example the day may start with SE eddy winds

So let’s start our baby steps by how we would forecast an easy wind pattern at Stinson:

1, Uncommon summer W-WNW ocean wind pattern.

This a very easy pattern to forecast. Most commonly in the spring and summer, the North Pacific High’s surface NW winds at the ocean buoys are NW and reach the coast as NW winds then curve into the Bay.

But sometimes the North Pacific High’s surface winds turn W. or the pressure gradient routes through the Bay Area cause the NW wind to curve as more westerly winds near Stinson.

You can see this in this image. Notice that the wind is NW offshore but turns more WNW in the Stinson to Golden Gate zone.

The next image show sensors in the Bodega to Stinson area.

Notice how Bodega  sensor shows NW winds while

the Pt. Reyes sensor shows WNW winds while the Stinson sensor shows W. winds to 18.

Also, note how the Tomales Bay sensor near Grassy Point also shows W wind as does the Inverness sensor and sensors towards Petaluma.

This is important since it means there will not be strong afternoon winds coming down from Tomales through the Olema Vally to Stinson as offshore winds fighting with the inbound ocean winds.

Life Cycle of the West Coast Thermal Trough

On this September 12,  we had more rain showers in the Gorge, first drops making it past Mosier since June!

Most likely we will be bidding farewell to those heat waves of summer, of which we had plenty, injecting triple digit heat and wildfire smoke over the Northwest.  The feature we see often mentioned in the forecasts, is the Thermal Trough, really a thermally induced trough, a tongue of hot air extending most reliably from central to northern California, into southwestern Oregon. In its usual, more limited phase, it critically affects the winds of the South Coast, where Oregon windsurfers know, the strongest ocean winds most often live.

This image depicts the pressure gradients, temperatures and wind barbs of a classic summer day for the Coast and Gorge. Note the heat of the Great Basin in grey, and the tight isobars indicating westerlies over the Central Gorge, and along the South Coast for northerlies, a ripper for both places…..



Here’s what happens when the thermal trough gets more expansive, in over the Cascades. Note the wind reversal over the Gorge…these hair dryer easterlies can easily fan wildfires as they did last year at Eagle Creek, while downslope winds off the west side of the trough, bring sunny hot days to Portland. Coast winds usually build up toward Astoria during this time, while maintaining the blistering pace at Pistol.



Here the thermal trough is all the way over the Coast range, and even heating up the South Coast, moving greater pressures for northerlies, up toward Astoria and the North to Central Coast. Modest to moderate easterlies maintain for the West Gorge, yet another day.


Holy Heat wave….here the Eastern Gorge is extra hot with light winds, easterlies are milder in the West Gorge, and north winds  more confined to the northern Oregon Coast, and WA shorelines too. A southerly marine surge often accompanies this scenario with fog creeping up the Coast, starting here at the California border with mild southerlies.



Now we see the set up for the marine surge to bring cooler air back to the Gorge, after the fog makes it all the way north. This makes for a solid WNW day at Jones Beach, and maybe mid to upper teens westerlies in the Corridor and Stevenson. The cooler air can be noticeable near Hood River, and often the next day is a good strong westerly from Swell City to Dougs, with the cloud bank filtering even further up the Columbia, sometimes past Stevenson.

Ending the cycle of  that thermal trough, a common summer pattern as we experience it here in the Gorge and on the Oregon Coast. Other parts of the world also have thermal low patterns, such as Australia, Saudi Arabia, and India-Pakistan.  In our case the extreme heat created in the interior southwest U.S., sets up a large scale pressure gradient with the North Pacific High offshore, which can have many configurations during the summer season. Now we move into autumnal cycles of upper troughs and frontal waves, as the North Pacific High starts to wander off for its winter sojourn further south…

Ref:  Brewer, Mass, and Potter, 2012 : The West Coast Thermal Trough: Climatology and Synaptic Evolution. https://journals.ametsoc.org/doi/full/10.1175/MWR-D-12-00078.1

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West Coast Wind Blog: The North Pacific High is under siege from the N. & S yet…

The NPH is still creating an eddy near San Francisco.

by Mike Godsey, mike AT iwindsurf.com 

For weeks the Bay Area has seen one counter-clockwise spinning eddy and/or low-pressure system to our west. The resulting southerly coast wind has held the typical NW coast winds far from shore. The result of all the southerly flow has made for the worse Waddell, Coyote and 3rd. Ave. season in many years while greatly benefitting Pt. Isabel, Larkspur, Brickyards/Peacock Gap and often Sherman Island.

Today, Sept 4, 2018, the North Pacific High is under attack from the north by a wintry Gulf of Alaska storm as well as a couple of tropical storm west of Baja.   But, as you can see in this animation, the North Pacific High still continues to create a counter-clockwise spinning eddy just west of the Bay Area.

Why? Notice how the isobars of the North Pacific High are bulging inland into far Northern California and the Pacific Northwest. This makes our ocean winds and the winds aloft turn from NW to more NNW to even NNE. And this, in turn, creates a combo of wind shear and a low pressure to our north that stirs up an eddy.

We should see a return to a more typical NW coast winds this Friday.

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:

“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

“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!”

“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.

ENE Wedge Upset by Yet Another Short Wave

Blog by WeatherFlow meteorologist Shea Gibson 8/25/18

Concerning yesterday’s drop in winds and shift offshore along the Charleston beaches, there was a solid ENE build near 20kts that dropped significantly for locales north of the Charleston harbor entrance and slipped offshore a bit. When something like this happens, there is usually a “short wave” involved that interferes with the local gradient, which has effects on the directions and speeds. A short wave is sort of a buckle or “kink” in the atmosphere where either a trough or an old front exists. It usually attempts to develop an area of surface low pressure, which ultimately affects surface winds.

Here is the IOP Pier archive from Friday, August 24 showing the drop in speeds and shift in direction.

Folly Beach showed something similar, but not quite as affected.

So why the shift and drop in speeds? This time, it was a short wave of Low pressure in association with an old front well offshore that buckled towards the coast and temporarily disrupted the local ENE gradient. This also upsets the local Sea Breeze oscillations and squashes the local build temporarily until the short wave dissipates or moves away.

This is the typical scheme for the oscillations, so when a short wave interferes either offshore or onshore, it takes away the dynamic forcing (stronger winds along the barrier islands) and weakens the lower pressure at the coast.

So next time you are out and this happens, you’ll know at least one major reason why it could be occurring. As forecasters, we sometimes mention the possibility as these features can be rather sneaky at times. This one definitely caught me off guard…so this is a lesson learned not to turn my back on the Gulf Stream with an old front over it.

Until next time, stay safe out there!


Shea Gibson
WeatherFlow Meteorologist
SE Region/ East Coast /Tropics
Twitter: @WeatherFlowCHAS


Outside Sources: SPC Mesoanalysis: https://www.spc.noaa.gov/exper/mesoanalysis/new/viewsector.php?sector=17


West Coast Wind Blog: Today’s eddy

Large weak eddy brings southerly winds to much of Bay Area.

by Mike Godsey, mikeATiwindsurf.com

West Coast Wind Blog: Lane and North Pacific High double team Hawaii

Strong trade winds supercharged by powerful hurricane winds threaten Hawaii.

by Mike Godsey, mike AT iwindsurf.com

NWS: Hurricane Local Statements

Issued: 21 Aug 2018 5:27 am HST

A Hurricane Watch has been issued for Big Island Interior, Big Island North and East, Big Island Summits, Haleakala Summit, Kahoolawe, Kohala, Kona, Lanai Makai, Lanai Mauka, Leeward Haleakala, Maui Central Valley, Maui Leeward West, Maui Windward West, Molokai Leeward, Molokai Windward, South Big Island, and Windward Haleakala

Situation overview

Hurricane Lane is expected to turn northwest toward the main Hawaiian Islands later this week. As Lane approaches the Big Island the south through west sections of the island may experience tropical storm conditions with winds 30 mph or greater starting on Wednesday night.

Deep tropical moisture associated with Lane will spread across all islands.

Expect periods of heavy rainfall, especially along the southeast and east facing slopes. Storm total rainfall amounts of 10 to 15 inches with local amounts greater than 20 inches possible.

Swell generated by Lane could bring very large and rough surf and dangerous rip currents for south and southeast facing shores.

Looking at the first part of the animation above for tomorrow it just looks like a day with especially strong trade winds from the North Pacific High.

Notice the typical venturi effect in the channels between the island.

However, the second part of the animation shows the approach of Hurricane Lane.

Currently, Lane is a category 3 hurricane with maximum sustained winds of 125 mph.

The next image, from NOAA, shows the probable pathway of the hurricane.

Now imagine those hurricane winds being funneled through those channels!

Notice that there is a cone of probability for the path of the hurricane.

This probability cone is not just a margin of error but rather a range of pathways from different computer models.

Meteorologist look at the output of each model and rank the relative accuracy in recent days and in the past to produce this cone.

The CNN graphic below shows the individual model tracks. Let’s hope that the GPS model is not accurate!

Lastly here is the iwindsurf.com version of the ARW model for the islands for today and this coming Thursday. Quite a difference!

Notice how the hurricane winds + NPH winds show the same venturi effect in the channels but also build on the crest of the mountains. Probably not a good time to visit Haleakala or sail S turns on  Maui.



West Coast Wind Blog: Heat wave ends but winds fizzle at many sites.

In meteorology, like politics, instability sometimes wins over stability!

by Mike Godsey, mikeATiwindsurf.com

This, I know is true:

  1. The Gorge is usually glassy calm during heat waves.
  2. At the end of a heat wave cool stable marine layer clouds flood the corridor from the ocean.
  3. Then very strong usable winds blow through the corridor towards Roos.
  4. The strong winds last for 2-3 days.

But… not this time!

“Times they are achanging”. Bob Dylan

“Life can only be understood backwards; but it must be lived forwards.” ― Søren Kierkegaard

So I set about doing an autopsy of Benjamin’s forecast which normally would have been a spot on forecast in these conditions. Of course, I have the huge advantage of 20/20 hindsight and the actual wind graphs which Ben lacked at 5:45 AM Saturday morning.

Part 1: Why the corridor fizzled and why the winds are going to be weak on the second day.

You all know how the Gorge is suppose to work.  A windless heat wave is followed by a massive surge of cool marine air and strong gusty winds from the corridor to Roosevelt.

But recent heatwaves have behaved differently with usable to even fun winds in the 4.7 to 5.3 range while temperatures were in the mid 90’s! (The reasons for that are interesting but for another blog.)

And normally in a post-heatwave pattern, the Hatch and Swell zone are not reliable in the morning until the clouds burn back then becomes strong and gusty in the afternoon.

So my plan yesterday was to watch the text reports from The Wall and go with the wind.

But as the texts came in it became clear that something was wrong out at The Wall.

And from my window, the Hatch became progressively worse as the day passed with only brief periods of useful strong wind.

The wind graph at the Hatch for yesterday August 11. looks pretty miserable with gusts into the 30’s and lulls in the 2 to 3 knot range. True there were brief times of usable winds but overall the winds were even worse than the graph depicts

I put the first hint of the coming fizzle in one of my mid-morning “Bluff Reports” for the Hatch and Swell zone. I mentioned that the clouds were not draped over the walls of the corridor, like you see in this dawn image, which is normal when AM marine layer clouds clog the corridor.

Marine layer clouds are comprised of heavy dense cool ocean air so it hugs the surface and flows over obstructions. This makes for relatively steady wind. Later in the day, I used the Skyline Hospital time-lapse feature to make the following animation.

Notice at dawn the flattened appearance of the marine layer clouds. An inversion of warmer air is compacting the upper surface of the clouds and because they are “heavier” than the air above them the clouds and the wind associated with them hugs the water.

Normally as the clouds burn back and the desert heats and the pressure gradient climbs this dense air would be sucked eastward and the wind would become stronger and steadier.But looking at the clouds in this animation notice how at dawn they have the compacted normal look of stable maring air. But watch carefully and you can see how unstable air arrives and shows vertical growth as the land heats.

This vertical motion disrupts the wind flowing along the river making for the big lulls in the corridor.

So where did this unstable air come from? Typically a heat wave ends as an upper trough at ≈ 18,000 ft. moves over the west coast. An upper trough is an area of cooler ascending air that is moving onshore. As this air ascends the marine layer clouds thickens and moves from the coast into the Gorge. This denser air has higher pressure while the still hot deserts have less dense lower pressure air hence a pressure gradient and strong wind.

But this Pacific upper trough was more like a Cut-Off Low and had been wobbling around in the Pacific for days. And more importantly, the Cut-Off Low/upper trough had supported a surface storm system with lots of cloudy unstable air.

You can see this near Cut-Off Low and the surface storm in this animation from several days ago.

So yesterday the heat wave ended as the remains of the Cut-Off Low and surface storm and unstable air came over the Pacific Northwest.

The satellite animation below starts at dawn yesterday. First, note the flat appearing slow-moving marine layer clouds extending from the coast into the corridor. If only these marine layer clouds had been present we would have had a typical strong windy end of the heat wave.

Now, notice the fast-moving puffy cumulus clouds appearing first at the coast and rapidly moving over the corridor of the Gorge. These are the same clouds you see in the Skyline Hospital time-lapse above.  These clouds are comprised of unstable air and they disrupted the surface winds flow. So the corridor saw exceptionally up and down winds.

So why are the winds so modest today when normally we have several days of strong wind at the end of a heat wave

Usually, upper troughs are over 1000 mile wide and move relatively slowly from west to east. But in the image below notice how yesterday’s upper trough is quite small and since it is moving fast it has almost departed from the Pacific Northwest.

That is why the marine layer clouds are so sparse today and why the winds are going to be weaker.

Part 2: Why Maryhill, Wall and Rufus fizzled.

Take a quick look at the texts from The Wall area above. At least at the time of those texts conditions where pretty miserable in that area.

The notoriously misleading Wall Marker 40 sensor appears to confirm those up and down winds. But what the wind graph does not capture is that the winds on the Washington side of The Wall were often much like the photo below.

The reasons for this have been covered in this blog about using the sensors in The Wall area. But basically, if you see any hint of West winds in this or nearby sensors you can expect weak UP AND DOWN winds at the Wall on the Washington side.





West Coast Wind Blog: The Grinches who stole the Gorge winds & where it’s stashed

Why the Gorge winds finally returned to normal.

by Mike Godsey, mike AT iwindsurf.com

Despite the recent unusual heat wave winds at the Hatch and Swell the Gorge has had long periods of mild summer wind despite the epic winds of May.

The phrase I hear repeatedly is “The Gorge is broken”

So what has caused the long heat waves and weak winds and where has all the wind gone?

This e-mail report from Crissy Field in the Bay Area is your first hint:

“Today, for the first time ever at Crissy, I rigged a 3.4. Finally after two day of being wildly overpowered on the 3.7, the 3.4 was like magic. It felt so normal and so good.

“It’s just crazy. Three days in a row I could have sailed 3.4 at Crissy in July!!! Different day, same wind. And you can imagine the swell at the north tower. The gorge has moved south. Come on down.

(my wife) on 2.8, (a friend who weighs 158) on a 3.0, Me (weighing in at 168) on a 3.4 Never would have believed this could happen if you’d told me in the past.”

Your 2nd and 3rd hints are in today’s model imagery below as is the most important hint ie. when the Gorge winds will return. So using those hints take your shot at explaining it all!

Well, the Gorge appears mostly fixed today. Compare the model output at the Surface and at about 18,000 ft. for Sunday vs. Today Tuesday.

Notice how the heat producing upper high pressure is exiting eastward. Meanwhile, at the surface, the North Pacific High’s is bars are now stacked over the Gorge making for a stronger pressure gradient. And also note how the inbound upper trough at about 18,000 ft. over the Gorge.

And the upper trough brings a cooler deeper marine layer air to the coast and towards Portland making the Gorge pressure gradient concentrate in the corridor and it also delivers SW flow just aloft which helps our surface winds a bit.


West Coast Wind Blog: Old vs. New satellite imagery for the S. F. Bay Area:

The NRL product still has some advantages.

by Mike Godsey, mike AT iwindsurf.com

The new GOES 16 satellite imagery has great tools and higher resolution compared to the old GOES 15 satellite.

However, as you can see in the 2 images below from this morning, The Monterey NRL, through the years, has tweaked the GOES15 imagery for the Bay Area so that it provides more useful detail than the 16 does at this point.

Looking at the 2 images below notice how the new GOES 16 does a better job resolving the edges of the fog. But the old GOES 15 does a much better job showing the first hint of Año Nuevo clearing near Waddell. And it shows the wave clouds streaming from Pt. Reyes towards San Bruno Gap that foretells strong winds just aloft.

Working on the GOES 16 imagery for a few minutes using the red channel I could improve visualization of these features about 50% so hopefully the NRL will do even better for their version.

For now the best feature of the GOES 16 page is using fwd/rev “time lapse”.