West Coast Wind Blog: Heat bubble expands over Belmont to Seal so up and down winds but…

Leo and Cabrillo are spared for different reasons.

Hey Mike,
 Long time no talk. Hope all is well and you’re having a great summer. I thought I’d share a weather thought from today’s very strong winds for Leo Carrillo.
I’m not at the beach today (too much weekend madness for my tastes), but checking the graphs I find it really interesting to have intensive heat at the nearby ridge tops in Malibu, perhaps record breaking, yet no heat bubble at Leo. I’ve never seen this happen before that I can recall.  Attached is the mesowest region map from 3:45pm 06/25. History always shows that when temps go over 100 in this zone, the beach is impacted by the heat expanding to the coast, yet the coast is still 73deg at the NWS sensor and 65deg at the iWS sensor. Maybe it will still happen later in the afternoon, but it sure seems strange and inconsistent to past personal observations.
It’s always a guessing game for me in trying to figure this out.
 Thanks for listening – stay well!
Mitch K 
by Mike Godsey, Mike AT iwindsurf.com
Hi Mitch,
Good to hear from you and thanks for the informative mail.
It is rare for me to forecast such strong winds at Leo. Pre dawn I was watching the temperature forecasts for inland valley sites near Leo that suggested that the heat bubble would be an issue for parts of the coast. In the image below notice how the isobars from the thermal low expanded over the Belmont to Seal area. In reality the pressures probably flow back and forth over the beaches in that area as the cooling ocean wind and the land heat interact. You can see that in the Belmont to Seal wind graphs where the impact of the heat bubble is indicated by the green arrows.
But I know from experience that in most thermal trough (aka “heat bubble”) situations Cabrillo is somewhat protected since the Palos Verdes Peninsula is surrounded by cooling water on 3 sides. So its wind graph looks much better.
 As your images shows 104 is clearly in the range that would could the heat bubble over Leo. But I reasoned that:
1.  The ridges behind the Leo area will slow the expansion of the heat bubble to the beaches so it might not close down the wind until very late afternoon.
2. With such strong winds at Leo the heat bubble would have a hard time getting the last mile to the beach.
3. The forecast inland winds were more W. and not pushing the heat bubble towards Leo
So I gambled and forecast Leo to have very strong wind without a heat bubble effect until evening when the fading winds would allow the bubble to cover the beach. You can see in the Leo wind graph this is pretty much what happened.
Win some, lose some… but this was a win!
Posted in Los Angeles, San Diego

West Coast Wind Blog: Low pressure off California…

Battles with subsidence from crushing high pressure heat wave.

by Mike Godsey, mike AT iwindsurf.com

A marine surge is arriving either tomorrow Friday or Saturday AM at the latest. These animations show some of the variables involved.


Posted in Los Angeles, San Diego, San Francisco

West Coast Wind Blog: Unusual Bay Area wind pattern likely Sunday June 18…

Makes forecasting very iffy

by Mike Godsey, mike AT iwindsurf.com

Take a look at the extended forecast for the Bay Area tomorrow. So what is going on?

As you may have noticed Bay Area wind patterns keep changing in last 10-20 years. They are very very different than the stable spring and summer pattern that prevailed for decades or longer.

And Sunday we will see a pretty crazy pattern. I will let the 2nd. graphic below speak for itself. Take a look at all the different wind patterns I have to deal with in trying to forecast this mess.

At the surface there will be NW, NNW, W, WSW, SW, S and even NE winds around the Bay Area while just aloft strong NNW winds prevail.

And the reality will be far more complex than this simplified computer output. So take tomorrows forecast with more than the usual grain of salt.

Posted in San Francisco

June Tropical Activity Stirring in the Atlantic Basin

By WeatherFlow meteorologist Shea Gibson

The start of the Atlantic Basin hurricane season is June 1st and goes through November 30th each year. Typically, we might see a few small homegrown or near coastal systems develop along tail end of cold fronts…or warm, moist easterly trade winds helping spawn a few tropical waves into the western Caribbean/Gulf of Mexico.  For the 3rd year in a row in the Atlantic, we have had a tropical cyclone develop before the official start of the hurricane season. Tropical Storm Arlene (April 19) was a fish storm pretty far out that looped around and was torn apart by an upper Low. More on schedule with its season (May 15-Nov 30) was briefly lived Tropical Storm Beatriz in the Eastern Pacific, which made landfall over southern Mexico and eventually supplied a good bit of moisture into the SE United States that helped drop record rainfalls in Florida (not good for flooding, but was good for their rather serious drought situation).

This is a more typical origination point we might see according to NOAA’s historical tracks.

What is not typical is to see tropical waves holding strength as they propagate westwards off the African coast along the ITCZ (inter-tropical convergence zone) this time of the year. This zone is an equatorial warm monsoonal trough zone where abundance of moisture is usually available for tropical systems to develop.  The ITCZ sits further south and slowly drifts northwards where development becomes more favorable later in the summer and into the fall during what is called the “Cape Verde Season”.   There is an area now being watched that the NHC is giving a 10% chance next 48hrs and 20% next 5 days.

This shows the wave coming off and heading west…and behind it is yet another (and rather impressive) tropical wave showing lots of convection as it enters over the Atlantic Ocean. There is dry air ahead and upper shear, so the environment is not that conducive. However, if it holds together further west, it could get pushed into the western Caribbean where those warm easterly trade surges may help supply more moisture into it. Very far off to tell just yet with a higher likelihood of it dissipating.

In this area, we watch for lifted and suspended Saharan Dust in the mid levels of the atmosphere to dry systems out, but in this case the wave is further south to escape most of the moderate effects. Important to note that this dust layering helps fizzle out many “would be” systems from developing and possibly becoming problematic for us in the US!

The other area being watched is near the Yucatan into southern Gulf of Mexico (Bay of Campeche), which has a medium chance now at 50% next 5 days.

The Sea Surface Temps are plenty warm at the top between 82°-86°F according to the latest NASA Sport SST 2km imaging.

BUT…we always look at TCHP (tropical cyclone heat potential), which does not look favorable for prime conditions in the southern Gulf of Mexico at the moment, but is increasing a bit as of present. Some of this information gauges the actual “depth” of the warm waters, which when stirred will cool quickly.


Models are beginning to split on which way this system goes, with the GFS taking it north and the EURO taking it west. We’ll have to watch for High pressure over the central United States and upper shear being a limiting factor in this area of disturbance. Nothing definite yet, and no immediate threat to land.

We’ll be keeping an eye on the tropics. Stay safe!


Shea Gibson
WeatherFlow Meteorologist/Wind Forecaster
Outreach & New Station Projects
SE Region/East Coast
Twitter: @WeatherFlowCHAS

Sources for graphics: http://tropic.ssec.wisc.edu/http://www.aoml.noaa.gov/phod/cyclone/data/np.htmlhttp://www.nhc.noaa.gov/


Posted in Coastal Georgia, Coastal South Carolina, Outer Banks of North Carolina, SouthEastern North Carolina, Weather Blog

West Coast Wind Blog: Sudden mystery Larkspur Eddy leads to…

 An autopsy of an East Bay wind crash!
 by Mike Godsey

If you were on the water near Pt. Isabel on May 28 or 29th at 3:30PM you remember those days well.ZZ0714475A If not take a look at this wind graph and imagine what it was like on the water.

The job of this blog is to solve the mystery of what caused that precipitous crash in the winds. Let’s start by taking a look at the image on the right of the typical weak 9:30AM  winds from Berkeley to past Larkspur. For lack of a better name I call this curving wind pattern the Larkspur Eddy.

Normally the Larkspur eddy is not worth mentioning in our forecasts. Sure long time Larkspur regulars know that summer commonly brings weak SE winds in the morning. And Berkeley and Pt. Isabel locals who drop by those sites to walk their dog know that often there are weak SSW winds in the morning. But those “eddy” generated winds always shift when the strong WSW winds build in the

But something really weird happened on May 28 and even more profoundly on May 29, 2017 that at first seemed totally mysterious. Both days the Pt. Isabel winds had an abrupt die off at about 3:30PM.

When things like this happens I try to do an autopsy of the forecast to help me learn to forecast days where a fade die off may happen. As you have noticed in recent years we warn of sudden die offs pretty commonly in the spring for Pt. Isabel and Berkeley and more rarely Treasure Island. But May 28th did not seem that sort of day.

Customer’s input:

So I put out a notice in my Sunday evening forecast asking for East Bay sailors and kiters to mail me their observations of the die off.

I got lots of reports about people floundering at 3:30 but 2 mails in particular had critical details that helped me start the autopsy. Check out the text in green in these excerpts from those mails.

Then the next day, with Kerry forecasting, the exact same event occurs but with an even more profound wind die off. So I really needed an autopsy of both forecasts.

Satellite imagery:

My first step was to animate the satellite imagery for that day. And sure enough a weird pattern of fog emerged. Watch this satellite animation and watch the fog burn back.

At 3:30 I have stopped the animation. Notice that the sky is clear both east and west of the Golden Gate. Now that is really strange since normally if there is coast fog in the afternoon then there is fog at the Golden Gate and often a streamer of fog heading towards Angel Island. But instead notice how parts of San Francisco are foggy. Now look even more carefully when the animation pauses and notice the streamers of fog from San Bruno Mt. and Twin Peaks. That shows that there are very atypical SSW wind over The City.

Cam Analysis:

To get a better handle on this I animated a Tiburon cam image of San Francisco from night to 3:50 PM. Notice that during the night and early morning there is the typical marine layer clouds covering the Bay Area. Then in theearly afternoon is narrows and becomes a broad streamer from the Golden Gate through the Point Blunt to Treasure Island Slot. All of this is normal.

Then watch carefully from about to 1:30PM to 3:50 PM. Note how the Bay clears and the fog appears to be SOUTH of the skyscrapers. This is not normal and reflects what we  saw in the satellite. So what is going on?

Wind Map Analysis:

Digging deeper I animated the Bay Area wind map to see how the wind changed at all the sites that afternoon. Looking at the wind map to the right notice how there is a weak Larkspur eddy in the early AM. Then WSW upper teens winds hit Pt. Isabel around 1:00 PM and the eddy dies.

Then abruptly at about 3:30PM  notice how the eddy reappears going all the way to Larkspur killing the Pt. Isabel winds.

Annotated Wind Map Analysis:

The next 3 images show how I developed a working hypothesis about how the eddy killed the Pt. Isabel and weakened the wind at other nearby sites.

The top image shows the wind flow at 2:30 PM. Notice that there is upper teens to about 20 winds from the ocean past Treasure Island to Pt. Isabel and on to Sherman Island.

Pretty much a normal day for Pt. Isabel.

Then in the second image notice that there is a sudden drop of the Pt. Isabel winds and the yellow wind arrows show shift to S. winds.

Notice how there are now SE winds at Larkspur but NW winds rippling over the Marin coast range.

Paradoxically this means we have two winds diametrically opposed on the bay  side of Marin!

Also notice that the Crissy and Sherman Island winds continue unabated during all of this.

This tells us that the pressure gradient to the Central Valley has not changed during all of this.

The third image in this series shows the steep and complex topography the NW ocean wind over Marin has to traverse.

Then notice the radical curvature of the winds from the Golden Gate to Pt. Isabel to Larkspur. You might think that all that would happen is that these 2 winds would collide but there is more to the story.

Relief  Map Analysis:

In the next set of two images from Google Earth I have exaggerated the vertical scale so we can better visualize the impact the Marin coast range has on this developing story

The top image shows the afternoon winds up to 3:30PM. Notice how the NW wind curves through the Golden Gate and passes by Treasure Island and over Pt. Isabel.

Also notice that the NW winds are barely penetrating over the coast range of Marin in the upper left corner of the image.

The second image reconstructs what happened for 30 minutes after 3:30 PM. My reasoning is that the NW winds finally climbed over the Marin coast range.  Then as they descended into the flatlands east of Kentfield compressional heating occurred jacking up the local temperature and creating a very local low pressure zone.

My hypothesis is that this low pressure  zone briefly caused the winds in the Berkeley Pt. Isabel corridor to change direction towards the Marin low pressure.

Analysis of model temperature forecast for Larkspur area:

To begin to verify this hypothesis I looked at the model temperature forecast from the 3km NAM. As you can see in the next image the model was forecasting a very local warm up in the bay shore of Marin centered over Larkspur. This supports my hypothesis.

Analysis of actual temperatures:

A better test is to look at the actual measured temps in the Larkspur area at that time. To do this I looked at the Intellicast temperature animation for the actual recorded temperatures from 5AM to 4PM. Look carefully at the time scale and the sudden heating in the Larkspur area around 3-4PM.


Why did our high resolution winds models not pick up this event and allow us to forecast it in advance so kiter, windsurfers and boaters would not be becalmed?

To keep the forecasts manageable we break the time slots into 2-3 hours slots. However this means  that brief events like this will not register. And even if we went to the max. time resolution possible a 30 minute even would only show as a decline in the wind. But even that would help people. So the next time I see this pattern I will try increase our forecast time resolution up so at least you have a heads up.

Your job:

There is a moral to this convoluted story. The key to better forecasts for your site is to send us information about any thing interesting that you see on a day we blow your forecast. Send messages to mike AT iwindsurf.com

Posted in San Francisco

West Coast Wind Blog: Wacky San Luis sensor readings…

Maybe the sensor is not broken?

by Mike Godsey, mike AT iwindsurf.com

Hi ctuna,

You are not the only one to notice the “wacky” San Luis readings. No we have not moved the sensor and there are no new structures near the sensor. But something has changed and that is the Bay Area wind patterns.

I know the wind patterns around San Luis very well since I was employed by GoogleX to do the forecasts for their Project Loon launches in that area:


So let me develop a hypothesis for you:

More and more frequently we are getting spring and summer northerly winds coming down the Central Valley. This change is related to increased # of NPH ridges we keep mentioning in the forecasts as well as the Golden Gate Eddy.

So what does this have to do with wacky San Luis winds? Take a look at the animation below and watch the battle between northerly and more southerly wind over San Luis.

The second illustration makes it clearer. The details vary from day to day and with the relative strength of the N. and WSW wind but basically:

1. In the morning the marine layer is often deep in Pacheco Pass and WSW wind blows at the sensor. See GREEN arrows and GREEN diamond on wind graph below for Pacheco Pass.

2. If there is northerly wind in the Central Valley (see RED arrows) it hits the hills just north of the sensor creating northerly turbulence. This northerly turbulence spreads randomly over the Forebay area.

So at some locations all you sense is the wind from the pass while other areas get mostly northerly wind while others get a mixture. The higher your location and the more easterly your site the more northerly wind you will feel.

You can see this by comparing all the archives from the surrounding sensors. But at our sensor so there is a battle between the N. & WSW winds. Hence the “wacky” readings (see ORANGE boxes)

3. If the northerly wind is fairly strong the sensor shows N. wind for a while.(ORANGE BOX)

4. Then in the early afternoon as the Central Valley pressure gradient goes up the WSW wind blows stronger at the sensor and the Northerly wind fades away. As this shift happens there may be a second period of “wacky” wind and the winds battle. Then the more southerly winds prevail. (2nd. green diamond.)

If you look at the San Luis archives for the month of May you will see the pattern of SW wind then N wind then SW wind punctuated with “wacky” readings very frequently. And on each of those days there was northerly wind in the Central Valley.

The reason you see different directions at different nearby sensors is the different frequency they update.

Our sensor updates more frequently than most of the other sensors so it shows more of the “wacky” changes.

Of course my hypothesis could be nonsense and actually it is a wacky osprey that lands on the wind vane each day to avoid the northerly winds and then takes off when the marine winds start.

Hopefully no one will ask why we are seeing more ridges, eddies and northerly wind!


Posted in San Francisco

SC Offshore Water Temperatures, Currents, and Fish

SC Offshore Water Temperatures, Currents, and Fish

Tim Kent


Spring is here, signaling the annual run of Dolphin fish off the Southeast Coast.  This fishery provides a large economic impact to coastal communities and coincides with warm water from the Gulf Stream shifting over the continental shelf where it interacts with cooler shelf water.  We will look at a couple days with different conditions to compare and discuss, where the fish may or may not have been.

Relavant factors

  • Water Temperature >70F (preferred 74F-80F).
  • Water Color – Blue to Cobalt Blue (related to chlorophyll).
  • Edges/Rips – Concentrate debris and baitfish.
  • Bottom topography in relation to the above factors.


4/18 SST

credit: Hiltons Offshore

  • Note warm water (74F-76F) eddy pushed in to the shelf waters inshore of the main Gulf Stream edge.
  • Also not finger of cooler (72F) upwelling water between the two water masses.

4/18 Chlorophyll (water color)

credit: Hiltons Offshore

  • Note color of water in corresponding warm eddy vs color of water in Gulf Stream and finger of cooler water between the two water masses.
  • Often chlorophyll, which indicates the presence of marine plant life, is higher (yellow) along boundaries between cool and warm waters, where currents are mixing up nutrient-rich water from deep in the ocean. Many of the temperature boundaries along the loops in the Gulf Stream are mirrored in the chlorophyll image with a stripe of lighter blue or yellow, indicating elevated chlorophyll.
  • Finished a stupidly long day with 8 dolphin and 1 skippy

5/16 SST

credit: Hiltons Offshore

  • Same area nearly a month later – note how much warmer the shelf water has become.
  • There is a finger of warm water (78F) pushed in to the SWB area extending down toward the 380 hole, but aside from that the main feature appears to be the gulf stream edge out deep.

5/16 Chlorophyll (Water Color)

credit: Hiltons Offshore

  • Note water color of finger of warm water inside the 380 hole vs surrounding water color vs Gulf stream edge water.
  • Finished a regular trolling day with 10 dolphin.

Now for the weather portion of the discussion, as both days were “fishable” by recreational boaters.

4/18 Sea State at Edisto Buoy 41004


  • Fading SW’rly wind chop from prior day with mild ~2ft of nicely spaced  (10-11s) SE’rly Swell.
  • Translated to pretty rough ride out into the first 10NM due to pinched coastal front laying right along the coast producing 15kts of NE’rly winds along beaches,  but pretty nice thereafter, and a very nice ride back.
  • Heading was of no concern as we were able to go directly where we though we should.

5/16 Sea State at Edisto Buoy 41004

  • Relatively light wind most of the day with a mild SE’rly swell (9s) and a pesky SW’rly wind swell from prior afternoon then again in the afternoon as Sea Breeze circulation expanded.
  • Translated to a relatively bumpy ride out, and pretty smooth return trip not counting the last 10NM in crappy SW’rly Sea Breeze chop.
  • Primary issue was not being able to take a more E’rly heading in the morning due to fear of plowing into SW’rly wind chop on return trip.

Morale of the story is that although we have lots of data to help narrow down the likely location of fish in the region, we are subject to sea conditions and the actual availability/density of fish in the region.  Two different trips yielded similar results, but in general the fish were not here in good numbers yet back in mid April, and we fished the wrong area most of the day in mid May.  Thats why they call it fishing and not catching!

Posted in Cape Cod

Draft about marine layer lifting.

Posted in San Francisco

West Coast Wind Blog: The heat is on…

Weak winds for Southern California and the Bay Area with eddy woes!

by Mike Godsey, mike@iwindsurf.com

Below is the Bay Area forecast for this weekend. Not very promising for most of the Bay Area and Southern California also has little promise for most sites. The following graphic tells the story. Watch the time line and the shape of the North Pacific High and how the ocean winds turn a less favorable NNW and eddies form.

Satuday: The North Pacific High tilts away from the Northern California coast and holds a large ridge into far Northern California and the Pacific Northwest. This ratchets up the temperature in the Bay Area into the 90’s brings light unfavorable NE winds and warming over us while holding the Central Valley thermal low over the Bay delaying and weakening the winds. The North Pacific High’s winds turn an unfavorable NNW so the coast winds fade. It looks like a tiny Golden Gate Eddy may spin up so the upper teens winds should focus on the Crissy to Treasure Island corridor with some of that winds reaching to the Olympic Circle but probably not Berkeley and Pt. Isabel. Coyote and 3rd. Ave. have upper teens potential in the Channel but the fate of the winds inside depend upon the Golden Gate Eddy. At this time it looks like the eddy may die around 4PM so there is a chance of WNW mid teen winds inside.

Sunday: Upper teens winds should focus on the Crissy to Treasure Island corridor with some of that winds reaching to the Olympic Circle but probably too outside for Berkeley and Pt. Isabel. Coyote and 3rd. Ave. have upper teens potential in the Channel but the fate of the winds inside depend upon that still unpredictable Golden Gate Eddy. At this time the winds inside look like WEST and weak.

Monday: The existing North Pacific High off our coast shrinks and recenters west of Washington state. So the NW wind totally fades away on our coast. A huge 200 mile counter-clockwise spinning eddy forms west of the Bay Area due to mesoscale low pressure at about 5000 feet elevation. WSW winds in the mid to weak upper teens focused at Crissy and Treasure Island and way outside. Meanwhile a huge new North Pacific High about 1500 miles wide forms north of Hawaii and begins to slowly march towards the California coast.

Posted in Los Angeles, San Diego, San Francisco

West Coast Wind Blog: Death of a Catalina Eddy and then….

NW winds move to the Southern California coast!

by Mike Godsey, mike AT iwindsurf.com

The Catalina Eddy is often a wind killer for strong westerly winds on the Southern California coast. But when the North Pacific High’s surface NW winds are especially strong they can blow out the eddy. The forecast for today looks like we will have that type of day today. These are large files so you may have to wait a few seconds for them to load.

The following 2 animations show how different models depict this process. 

Posted in Los Angeles, San Diego