West Coast Wind Blog: Eddy scenario likely Wednesday, May 22, 2019

by Mike Godsey, mikeATiwindsurf.com

You may remember that 4-5 days ago I mentioned in the extended forecast that the North Pacific High would really expand this week. As you can see below that the NPH now spans the waters from Alaska to Hawaii to the tip of Baja. I also guesscast that we might see an eddy setup develop towards the end of this week.

That scenario still looks likely and we should see an AM eddy tomorrow that fades midday. Then Friday the eddy becomes more prominent.

The images below show some of the steps in my reasoning. Eddies change very fast so it is still to early to forecast how all this will impact individual sites but the area north of the Bay Bridge is more likely to benefit.

West Coast Wind Blog: Front passes and southerly winds turn westerly an ROAR!

by Mike Godsey

ROUGH DRAFT text later today

Southern California and San Francisco Bay Area kiters and windsurfers know the drill. A storm passes then the North Pacific High move towards the coast and its NW winds curve into the beaches. Today we see a pattern that is more common on the east coast with prefrontal southerly winds turning into westerly post frontal westerly winds. These images tell the story pretty well by themselves but I will add more animations and text later today.

West Coast Wind Blog: North Pacific High finally makes a move on San Francisco IF Southern California Cut-Off Low moves southward.

by Mike Godsey

The satellite animation below shows a large counter-clockwise spinning Cut-Off Low over Southern California at ≈ 18,000 ft. Notice the fast-moving gravity waves rippling westward and northward from this disturbance.

Further north the North Pacific High’s surface NW winds are being bumped towards San Francisco. But for this to happen tomorrow, Saturday, May 11, we need this Cut-Off Low to move southward as suggested by the models.  Remember Cut-Off Lows are very hard to forecast.

 

West Coast Wind Blog: 24 hours in the life of a eddy

Eddy: May 8

Eddy: May 7

West Coast Wind Blog: Meet Eddy! The new weather landlord of the Pacific?



 

by Mike Godsey, mikeATiwindsurf.com

The satellite imagery below from today, May 7, 2019, really shows the lingering eddy in action. If you work the waters north of the Bay Bridge Eddy looks beautiful. But if the Peninsula or the coast is your home Eddy looks malevolent in this imagery.

For many decades the North Pacific High and its NW wind have dominated the Pacific west of California each spring. Sure, the North Pacific High took brief vacations to the south each time a storm arrived but like clockwork would pop back into place bringing NW clearing winds.

This year we have seen the near constant presence of an eddy off the greater Bay Area. Several times the eddy has almost died only to reappear along with southerly winds on the coast and much of the Bay.

Ironically, the eddy is created in large part by the North Pacific High being way too far north for this time of year.

What is causing the eddy? The proximal causes are easy. The North Pacific High has been aligned at an angle to the west coast so its normal NW winds are more NNW + there has been a near constant low pressure just to the north of the Bay Area.

But why is the eddy so early and so persistent? Watch for a future blog on the factors involved in the ultimate causation of the North Pacific High’s position and the resulting eddy.

West Coast Wind Blog: Excuses, Excuses… Now a Cut-Off Low + eddy make Bay Area & Southern California forecasting tricky.

by Mike Godsey,mikeATiwindsurf.com

For several weeks now our forecast team has been struggling with San Francisco Bay Area forecasting during a surface eddy pattern that is unprecedented in its duration and longevity. Now we have to add a Cut-Off Low up at ≈ 18,000 ft. to the mix. And there is a reason for the old rhyme “Cut-Off Low… weatherman’s woe” These beasts are hard to predict since they are cut off from the upper-level winds so they can wobble around randomly.

This animation below shows both the eddy at the surface and the Cut-Off Low at ≈ 18,000 ft:

If you have ever watched any eddy, from a dust devil to a tornado, you know they move around and gain and lose strength randomly as you can see in this video. Imagine trying to this:

https://www.youtube.com/watch?v=AwKc7H5gIWo

Our eddies are far larger and slower moving than a dust devil but they have still been making forecasting very difficult since a change in location and strength of the eddy midday can change the winds for each site especially near shore. And frequently we have had more than one eddy this season. So we are struggling to do the best forecasts possible.

If you are a newcomer to the Bay Area you should be aware that until recent years we and all the models were completely unable to even forecast the development of these eddies. This often led to wildly inaccurate forecasts where fog and SW winds would “magically” appear overnight shutting down the coast and parts of the Peninsula while bringing unexpected strong wind to sites north of the Bay Bridge. Now, it is rare for us to miss an eddy and slowly we are improving our forecasts during eddies.

So anytime you see the word eddy in a forecast you should use your knowledge of local fog patterns mid-afternoon to fine-tune the forecast especially for the winds near shore since the eddy may have moved since our 11:30 update.

 

West Coast Wind Blog: The earth vs. the eddy

Hi Gang,

Sunday, April 28: If you are a wind addicted kite or windsurfer the eddy is probably on your minds a lot recently. Either because it is wrecking your wind or because it is making great wind at your site. And right now it looks like some type of eddy continues for the next 6-7 days.

So it is a good time to step back and look at the BIG picture and get the eddy in perspective.

So take a look at this mind-blowing video of our planet and our eddy as seen from space at 9:45 AM this morning.

Mike

West Coast Wind Blog: Where sails and kites fill is determined by where Eddy Would Go…

by Mike Godsey, Mike AT iwindsurf.com

The meandering of eddies is unpredictable by their very nature of an eddy. Take a look at the eddy my banner above. As you can see it is positioned so it will shoot west wind through the Golden Gate towards Berkeley. Hence the famous Berkeley “T” you see in the imagery over Berkeley.

 

But now visualize the eddy being further to the south. That would mean more SSW wind that would favor Pt. Isabel as well as Larkspur and Brickyards/Peacock Gap.

It is very difficult to guess the position of the eddy at 6AM when we are preparing the forecast. That is why yesterday I issued the special update at 10:11 AM yesterday about the eddy and Pt. Isabel winds. 

Let’s take a look at yesterday and the eddy situation and see how it favored Pt. Isabel more than Larkspur, Brickyards/Peacock Gap and Berkeley and why the 3rd. Ave. winds INSIDE were much better than my forecast.

First focus on each of the counter-clockwise spinning eddies and their movement. Notice how they mostly fade in the afternoon.

Now, look at each of the gaps in the coast range as highlighted by the gray arrows and text.

3rd Ave.

Notice how the eddy action causes a build up of fog in the Hwy. 280 area and the Hwy. 280 area. My guess was that this would make for weak unreliable winds INSIDE at 3rd. I was wrong since as the eddy faded the fog stalled and 3rd. INSIDE was good. It is very easy to see this if you are in the area mid-afternoon. BUT forecasting this at 7AM or even 11:30 AM is challenging.

Larkspur

Now, look at the fog massing in the Muir Gap. Since this gap is at high elevation I was pretty sure the fog would not make it through the gap enough to help Larkspur and Brickyards/Peacock Gap winds. I was right.

The Stick, Tigers & Alameda

This was a tricky one and I forecast just upper-teens winds since I did not expect the fog to get to the top of the Alemany Gap. For the same reason, Alameda was not as windy as it can be in an eddy flow.

Pt. Isabel, Shimada Park

I nailed this one since the Golden Gate Eddy was in the perfect position to send a streamer of fog through the slot and over the Olympic Circle towards Pt. Isabel.

Anytime there is weak eddy flow or a weak marine surge be aware that the position of the eddy can change a lot from the forecast time to the time you reach the beach. So your best bet mid-afternoon is to watch the gap that feeds fog towards your site and make your own forecast update.

 

 

 

 

 

West Coast Wind Blog: Ships at Sea and using the right tools.

by Mike Godsey, mike AT iwindsurf.com

Note: This blog uses Southern California as an example of picking the best model using ship reports but the basic idea of the blog is relevant to all regions in the USA.

On winter days as I walk through the La Ventana campground I am always impressed by the thoughtful kiters and windsurfers who print out and post the day’s forecast on clipboards right where folks stand to judge the winds. But I also feel a bit downcast when I see the models they pick to print. Most of the time they pick websites that use the old GFS model. The same is sometimes even true for the web sites for local resorts as you can see in this, all too true, warning about the model output from the Captian Kirks resort.

Don’t get me wrong. The GFS model is great for following large scale wind patterns and is one of your best choices if you are forecasting storms or if you are a mariner. The problem is that the GFS resolution is too low to properly factor in the topography that so strongly impacts the wind at most launch sites.

The trick in forecasting anywhere is to know which model, on any given day, is doing best at capturing the reality of the wind later that day. And that takes years of experience as well as knowing how to interpret satellite imagery, weather balloon reports and, and yes, even ship reports.

Let’s take a look at this Southern California day as depicted by the windy.com web site and how well the ECMWF 9 km model did forecasting an eddy compared to the NAM 3 km model.

The first part of the animation shows the ECMWF 9 km forecast for an eddy over the Southern California Bight. Notice how the forecast eddy spans almost the entire middle portion of the Bight. This large eddy is supported by the NNW winds you see in the upper left corner of the image. It is also supported by a thermal trough extending from a low pressure just north of the Sea of Cortez. Note how the modeled isobars of the thermal trough cover the entire Southern California Bight.

Such a large eddy could easily keep the afternoon beach winds very weak. So in forecasting, we have to determine the accuracy of this model output. Sometimes we can do this by looking at the swirl pattern of the marine layer clouds in the satellite imagery. But often that imagery is too fuzzy at 7AM. Another way is to look at wind reports from ships traversing the area.

As you examine the ship wind reports below notice that the furthermost south ship report does not jibe with the ECMWF modeled eddy.

Now, look at the NAM 3 km animation. Notice how the NAM has the isobars of the thermal trough more focused in the northern Southern California Bight. Now looking at the ship reports notice how their wind reports more closely follow the modeled eddy winds.

So, in this case, I would tend to forecast the eddy dying midday and wind peaking in the Long Beach area. Why, because I picked the right tools for the job which in this case was using the NAM output and ship reports.

 

 

West Coast Wind Blog: How the NPH and convergence aloft helped jazz up our surface NW wind

by Mike Godsey, mikeATiwindsurf.com

As you can see in my banner animation above lots of sites had strong wind yesterday. The day played out pretty much as outlined in my 2 recent blogs about convergence aloft and the two NPH’s merging.

This blog shows how the surface winds you see in the banner were related to the winds aloft.

The first image is from the Bodega 449 MHz profiler. Notice that the time axis goes from right to left.

I have circled the very strong afternoon NW winds in the 25 to 40-knot range that the profiler picked up from near the surface to 500 meters aloft.

As these winds hit the Bay Area’s complex topography a bit of their momentum is transferred to the surface winds which you experience as gusts, lulls and shifts.

The second image shows the gusts, in red, of the RAWS sensors about the greater Bay Area. Note the very strong gusts on sensors located on hilltops.

Typically these strong winds aloft will subside on the 2nd or 3rd. day of a big NW wind event. This occurs either because:

  1. The North Pacific High moves away from our coast or
  2. Because the convergence aloft shifts away from us or
  3. Because part of the NPH moves inland to our north creating NNE ocean winds and unfavorable NE winds just aloft over the Bay Area. Both of these events make it harder for the wind to curve into the Bay.

However, at this time it looks like a huge North Pacific High will squat over the waters between California and Hawaii for 4-5 days. It has a lot of support from an upper ridge and convergence stays fairly close to the west coast.

 

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