The North Pacific High’s surface NW winds return…

…as the battered old North Pacific High merges


with new North Pacific 


by Mike Godsey,

It has been a wild 9 days of unending SW flow and Sherman Island and East Bay winds such as we used to see a decade or two ago. And the Sherman Island wind distribution was much more like we used to see in the old Rio Daze. Meanwhile the coast and most of the Peninsula had a 9 day wind drought.

But by Thursday July 24 the NW winds should return. It will not be an epic or even major NW event rather it will be the resumption of the typical combo winds
NWflowReturnswith SW thermal winds combining with NW ocean wind.

But it is a pattern that will spread the wind focus much wider so it includes Crissy inside, Waddell and the Peninsula. Since we are moving into a warming pattern Thursday the winds may be late and modest but at least with a NW component.

The imagery below shows how the long absent old North Pacific High west of the Pacific Northwest will begin merging with a new North Pacific High west of Baja over the next 2 days to bring this switch from SW to NW flow.

And at the bottom is the interesting story about how we forecasted these SW winds in advance

SWtoNW. Monday July 14, following my lead, Claire issued a 7AM forecast for another hot day and modest Sherman Island winds. Early that morning, spurred by a graduate student which whom I had be talking to, I was doing some research on the Southern California Catalina Eddy.

The Catalina Eddy is a large counter-clockwise spinning eddy that often spins up in the zone from San Diego to just past Los Angeles and can be a wind killer for Southern California.  I noticed that the Catalina Eddy was huge that morning and extended way west of the Channel Islands and even north of Jalama and Point Conception. Curious as to what caused this expansion I noticed that there was a mid level (700mb) low pressure system just SW of the eddy. I quickly realized that this low pressure was venting the Catalina Eddy, that is sucking air from the center of the eddy causing it to turn into a surface low pressure.

I then followed the modeled trajectory of the 700mb low pressure and realized that it ran northward along the west coast. This meant that if the former Catalina Eddy followed the mid level low pressure we would have a giant eddy heading towards the Bay Area. And its  counter-clockwise spiraling winds would mean SW flow and a deeper marine layer for the Bay Area for a day or two.

So I shot Claire the following hedge to insert as a bullet at the bottom of her forecast: “Chance of atypical SW marine surge from a huge expanding Southern California Catalina Eddy late today. “

I knew that some of you hate such hedges so I posted the message on the forums titled 3 Videos: Weasel words in the forecast: marine surge. If you missed this blog check it out to see why we had the long stint of SW flow.

Now almost 10 days later the SW surge is poised to fade  and NW winds should begin to ramp up.


Posted in San Francisco

Bermuda-Azores High Reigns in July.

by WeatherFlow meteorologist Shea Gibson

We are currently seeing a very seasonal summer setup with vast blocking Bermuda-Azores High pressure over the North Atlantic Ocean. As it assumes its typical 1024mb status and keeps more of a near-Bermuda presence, we are seeing periods of strengthened Sea Breezes along the SE Region off the synoptic Southerly flow it brings.  We usually see a few types of scenarios unfold with some variances as High pressure meanders back and forth:

1. Center(s) of pressure holds to the east with some north or south movement. The subtropical ridge extend westwards from the Azores with weaker synoptic flow…sending axis placement somewhere along the Carolinas to keep light or modest flows and increased moisture.

2. Centralized pressure builds closer to Bermuda and becomes more robust for a solid synoptic flow along the eastern seaboard of the United States.  In this case, the ridge axis usually drifts south into southern Florida for their typical light-to-modest seasonal flow and builds Sea Breeze profiles to the north (as seen the 2nd week of July).

3. Bermuda High blocks cold fronts from progressing offshore and holds them along the SE Region. EAST-WEST positioning occurs where northeast Gulf High lays it horizontal as northern continental High pressures pass to the east. This leads to a monsoonal type of environment with Gulf moisture being pulled along the boundary by Low pressures tracking along it (visible in the 4tht week of July).

One impressive feature for the second week of July was how vast this area of High pressure became. Notice how pressure built to 1032mb’s and took up the entirety of the North Atlantic above the ITCZ (Intertropical Convergence Zone).  The Saharan Air Layer (SAL) to the south remained fairly strong as dust storms in Africa continued to spill desert dust in the low/mid levels out over the Atlantic. This kept the southern portion of the High very dry… and dissipated several tropical waves.

Blocking High 7-10-14

SA NWS 7-10-14

Here’s the Saharan Air Layer for the 2nd week of July…

SAL 7-10-14

And here are the resulting afternoon Sea Breezes along South Carolina from July 7 to July 10 (Isle of Palms Pier sensor). You can see how the 4 day stretch starts out weak and ends weak during the nocturnal periods. This is significant in the fact that cold fronts have been stalled just inland or overhead of the coast.


Here are the local effects to the SE coast:


The 2nd week of July brought another round of strengthening Sea Breezes where the High pressure centralized closer to Bermuda and assumed the natural 1024mb status:

Blocking High 7-15-14


And here is the Saharan Air Layer that looks to be easing off the extended dusty stretch for the 3rd week of July…may finally allow some of those weak tropical waves to make it to the Caribbean and/or GoMex.

SAL 7-15-14

And here is the pattern continuing to block frontal progression off the SE coast through July 21 with northeast Gulf High keeping the EAST-WEST bending of fronts while northern High pressures pass to the north. Lots of precipitation through the SE Region due to abundance of Gulf moisture being pulled along the boundary.




The Saharan Air Layer has relaxed this 4th week of July enough to even allow for tropical development. Went from 20% chance to 70% chance within just a few hours, so we shall see what happens. Ya never know – it might be in the next WeatherFlow blog from the SE Region. Currently labeled as Invest 92L and will be “Bertha” if named. We shall see.

NHC 70% SAL 7-21-14




This blog may be updated to include the final 5th week of July so stay tuned…the goal here is to get the entire month.



Posted in Coastal South Carolina

Bay Area SW flow continues….

North Pacific High’s north winds maintain an eddy.

by Mike Godsey,

Welcome to July 1994! Like the last several centuries the San Francisco Bay Area is having the normal July SW flow with a deep marine layer! Today that moist  chilly blanket is snugging over the hills of Herb Caen’s  Bagdad-by-the-Bay. There are many causes of this foggy SW pattern and it is worth studying them since the long range climatological models suggest that these SW patterns will diminish in future decades. Probably by 2110′s NW winds will prevail most of the summer which will radically change the wind pattern in the Bay Area making Waddell and the Peninsula more reliable and Larkspur and parts of Sherman Island less reliable.

This last weeks forecast started off with dire warnings of  a heat wave and faint winds everywhere even Sherman Island. Then Monday 14 I had Claire insert a hedge into the weak wind forecast saying that there was a chance that a marine surge would hit that afternoon.

Trying to cover our a$$es I also put a bunch of videos on the forum under the title “Weasel Words” that depicted a large eddy evolving in Southern California and quickly moving up to the Bay Area creating SW flow.  You should review those Weasel Word videos now to see how we got to where we are now.

eddySWflowCUIn this first video you can see what the eddy looked like yesterday in the satellite. First note how the North Pacific High’s wind, on the left edge of the video, is moving from the N. to NNE rather than the typical NW. Notice how this helped create a giant counter-clockwise spinning eddy west of the greater Bay Area. Don’t confuse this with the tiny Golden Gate. This creature spans a hundred
times as much area as the punk eddy.

Now look at the cloud movement near the shore of the Bay Area and note how it is SW. This SW flow tends to bring moist warmer air from the pacific to the south over the chilly near shore waters produced by upwelling. So the moisture condenses and forms fog. This foggy air is attracted to the Central Valley low pressure. However with north winds the most intense low pressure in towards Redding in the northern Central Valley. The means the SW flow is mostly funneled through gaps in the coast range that face SW such as the Hwy. 92 gap, the Sherman Island gap and the Muir gap feeding Larkspur.

You can see this flow pattern more clearly in the 2nd video that shows the modeled wind yesterday. Note how the eddy winds are actually quite weak. But the venturi effect that occurs as they are funneled through gaps jacks up the wind as does the strong pressure gradient to Redding.

Going back to the first satellite image notice how this foggy SW flow disappeared as the air heated and the water vapor evaporated. But check out what happened when this moist air climbed to the cooler elevations of the Sierra Nevada. Thunderstorm time!

Of course the big question is what is making the ocean wind west of the Farallon Islands so northerly. To answer that question we have to look at the big picture. In the 3rd video notice how the NPH is huge and lords over the pacific. But also notice how far to the forth its clockwise spiraling  winds are located. This location, west of the Gorge, leaves the Bay Area NPHeddySWflowwith only N to NNE winds. This means that the ocean waters near the Bay Area shore only have weak wind since they are in the lee of Cape Mendocino and at the Sonoma coast.

These same north winds have to climb over the mountains north of Redding and Sonoma. And as those winds descend to the Central Valley they compress and, remembering the gas laws from your college chemistry class, you know they will heat making a strong low pressure in the northern Central Valley. So as the north ocean winds reach the latitude of the Bay Area they curve in following that pressure gradient and at times even make an eddy. Which in turn makes SW flow in the Bay Area.

Now in 1994 this type of pattern will occur much of the summer. But if you are still around in 2014 people will be saying what went wrong with the weather since they will have gotten used to more NW flow much of the summer.



Posted in Los Angeles, San Diego, San Francisco

Giant eddies SW winds fight NPH’s NW winds and the victor is….

The NW winds RULE this afternoon!

by Mike Godsey,

See the barely spinning 200 mile in diameter eddy NW of the Bay Area. The last several days this eddy was just west of the Bay Area. GiantEddyNPHSince the winds are circulating counter-clockwise around the eddy we had SW flow ocean wind which favors Sherman Island and the East Bay . But the eddy has lost the upper level lows that created it and it is now wandering off away from the Bay Area so the SW ocean flow is long gone in our area.

Now find the center of the North Pacific High in the SW corner of the video. Notice its clockwise spinning wind. This means the NPH has NW winds on the California coast. But in the AM today those winds are focused way south of the Bay Area. Why? Because, as you can see in the video the eddy is diverting the NW winds so they do not reach the California coast until south of the Bay Area. This afternoon the eddy breaks down and those NW winds really ramp up on the Bay Area coast.

Posted in Los Angeles, San Diego, San Francisco

Tiny upper level low creates……..

Surface eddy and SW flow for the Bay Area GiantEddy 

by Mike Godsey,

I will add more text to this blog later today but right now the wind calls so this has to be brief.

Yesterday, July 9, the S. F. Bay Area saw strong SW flow that really jacked up the Sherman Island winds while messing up the wind at many sites that are normally wind.

So where did all this SW flow come from? The proximal cause is clearly illustrated in the first video.

Note the huge counter-clockwise spinning eddy over 200 miles wide west of the Bay Area. Don’t confuse this monster with the common tiny Golden Gate eddy that forms just west of the Golden Gate. The typical size of the Golden Gate eddy is indicated by the  ”O” in the video.

The big question is “What causes this monster eddy you see in the video?”

The next set of images will give you the picture and I will provide the words later today.


Posted in San Francisco

A Bird’s Eye of a Hurricane.

…by WeatherFlow meteorologist Shea Gibson, July 9, 2014.

There has been evidence of birds becoming trapped in tropical storms and hurricanes in the past as several species have mysteriously showed up in places where they would not normally inhabit nor breed following these storms.  Locations include far inland areas where sea-faring birds have been found.  Evolving Doppler technology known as Dual-Polarization Radar or “Dual-Pol” for short, has been successful at catching these birds during their scans.

Below is a typical find in Dual-Pol with birds – as they can tell the size of moving objects captured in the scans. They can even determine what type of bird it is.


Here is an excerpt from the book “Taken By Storm” (by Lourdes B. Avilés) about The Great New England Storm of 1938…with reference to bird observations and later reference to observations during Hurricane Gloria in 1985.



In August, 2011 during Hurricane Irene, this was captured:

NOTE: “While this [bioscatter]may indicate mostly insects that would advect with the background flow rather than strongly flying, the high reflectivity values in these regions (20–401dBZ) indicate many birds are likely present, especially given the lack of observations of significant insect arrival when Hurricane Irene made landfall.” Journal of Atmospheric and Oceanic Technology VOLUME 30 by Van Den Broeke



Recently, UAH Severe Weather Institute Radar and Lightning Laboratories caught this image of birds in the eye of Hurricane Arthur:


From UAH Severe Weather Institute Radar and Lightning Laboratories:

“The power of dual pol radar. Likely birds trapped in the eye of Hurricane Arthur using reflectivity and ZDR (differential reflectivity)”

From the National Weather Service Wilmington WFO about this image:

“This image of Hurricane Arthur was taken from the Newport/Morehead City radar late in the evening on July 3rd. The left panel is your typical radar reflectivity image. The right panel is a new radar product called “Differential Reflectivity” only available since the upgrade to dual-polarization radar technology. It shows the difference in reflectivity between raindrops measured by a horizontal radar beam versus a vertical one.

Since most raindrops, snowflakes, and hailstones are close to being spherical, differential reflectivity is usually small: 0 to 2 dB. However in the eye of Arthur we see huge differential reflectivity values in the 6 to 7 dB range. What could be that much wider (more reflective horizontally) than vertical?

The answer, we believe, is birds. Hurricanes have been known to trap sea-faring birds in the eye and carry them along with the storm, depositing them hundreds or even thousands of miles from home. Hurricane Hugo back in 1989 took hundreds of seabirds into western North Carolina, depositing them on lakes near Charlotte. There is already one report of Hurricane Arthur depositing a Black Skimmer on a Canadian beach almost 1000 miles from North Carolina:


And here is the science behind the theory of birds in the center of hurricanes via PDF:

Polarimetric Radar Observations of Biological Scatterers in Hurricanes Irene (2011) and Sandy (2012)

Posted in Coastal South Carolina

Video: Upper trough, inbound from the pacific, hits Gorge and Bay Area June 2.

Decreasing temps and increasing clouds marine layer and SW wind aloft.

by Mike Godsey,

Upper troughHitsGorgeBay

Posted in Cape Cod, Los Angeles, San Diego, San Francisco

Sea Breeze Coupling for inner RI Waters and Buzzards Bay

Quite common in the early summer setups are these high pressure surface ridges that just… barely…nudge…. off.. the… coast.    People don’t believe me when I say yes there are situations with Rhode Island will see stronger winds than Cape Cod, but days like this is one of those situations.

Here is the general Sea Level Pressure prediction for this afternoon:   Note the ridge slipping slowly east which still supresses the winds on eastern Massachusetts but enhances the sea breezes in Rhode Island:

model ridge

Here is what happened as of early afternoon.  Note I marked the area where the winds are favored to couple into inner RI and Buzzards Bay.    Why doesn’t the wind get stronger on the RI south coast?   Well… the ocean temps are still quite chilly and there are winds there, but the synoptic winds tend to be warmer and skip over the south coast but mechanical mixing and venturi effects in the inner Bay help the winds accelerate there.

sweet spots

Another item to look at is the visible satellite because what can kill these winds are overblown thermal cloud buildup, or high clouds.   Note the shot from this afternoon and popcorn like clouds indicating good thermals and not much cohesion to stop the sea breeze circulation:


So how did we do?   Not too bad (if I do say so myself)….  given all models were showing not more than 6-10 knots for the afternoon, we bumped all inner Bay sites up for the afternoon in RI and did the same for Buzzards Bay.   In hindsight I should have listened to my gut instinct more and upped the numbers earlier in the day:

met forecast


How did the National Weather Service marine forecaster do?  Well…  even though we are urging them to use our data, here was their forecast for today:  S winds 5-10.



We’ll keep on the NWS to help them improve but since we have the stations located on the water for 20+ years, we have learned and are continuing to learn the nuances of these complex coastal areas and can verify our forecasts thereby learning from our mistakes.

We encourage our members to give us direct feedback at the bottom of every forecast that comes straight to our forecasters to help us improve.

Posted in Cape Cod, Rhode Island

Upper ridge blankets west coast by Monday.

How an upper ridge impacts Southern California, Gorge and Bay Area winds.

by Mike Godsey,

In the first video we are looking at  a model projection of the upper level winds at the 500mb level (  around ≈ 18,000 ft.)  from Friday 28 through Monday.


At the start of the video notice the very warm air (reddish color) west of Baja. Notice how these upper level winds for a bulge that each passing day this bulge moves northward. This type of bulge is called a ridge. First the ridge covers Southern California then Northern California and finally by Monday the Gorge.

The air mass within this upper ridge is warm and descending which compresses as drops towards the surface. This heats the surface air and creates a surface low pressure area. This low pressure ares then expands and moves closer to the coast. I know it seems counter intuitive that high pressure  aloft creates low pressure at the surface. But just think upper level high pressure creates heat at the surface and heat causes the air to expand so the pressure is lower. And as that low pressure increases in size to enlarges in all directions so it move closer to the coast both in Southern California, the Bay Area and The Gorge.

So what does this upper ridge do to the major kiting and windsurfing venues on the west coast?

Gorge: Note how The Gorge starts off yellowish (cooler air) and then becomes red as the  upper level ridge slides  up from Baja by Monday. Once the upper ridge is over the Gorge the winds

fade away as the surface low pressure expands over the region from the Columbia basin. With low pressure in the Gorge there is no pressure gradient over most of the launch sites. But late in the day when the low pressure retreats from the coast Jones Beach may have a decent pressure gradient.RidgeBajaCAheat

Southern California: Normally an upper level ridge means good coast winds for Southern California especially in the Cabrillo to Sunset corridor.  This happens as the surface low deepens and moves closer to the coast making for good beach winds.

And if it is really strong upper ridge and it the North Pacific High pushes a surface ridge into the Great Basin at the same time Southern California will rip. But if the upper ridge creates too much heating the thermal low pressure (aka “heat bubble”) will expand over much of the coast killing the wind as it does in The Gorge.

Unfortunately this upper ridge is too weak for this to happen plus an atypical Catalina Eddy will limit the Southern California beach wind.

Bay Area: The Bay Area undergoes the same process as the Gorge on Monday as the upper ridge causes the Central Valley thermal low to expand to the coast. But unlike the Gorge the Bay Area can still have at least upper teens wind late in the afternoon even during most heat waves. This happens for the same reason that Jones Beach in the Gorge can blow in the late afternoon. (see above)

The second video shows what the upper ridge looked like on Friday 28 as it first started its expansion  northward.




Posted in Columbia River Gorge, Los Angeles, San Diego, San Francisco

Two videos: North Pacific High returns to Bay Area waters Saturday

So NW flow ramps up on our coast and the Peninsula.

by Mike Godsey, mike@iwindsurf.comNWwindSlidesUptoBay NPHnwWindSlideUPCoast

Every read the phrase “tomorrow the North Pacific High’s surface NW winds will slide up the coast from  Southern California and focus  on the Bay Area” and wondered how can wind blowing from the NW move to the north.?

Well tomorrow, Saturday, this is exactly what will be happening and to help you understand the process study these 2 videos. And then tomorrow I will explain what is going on in case you are still lost.

In the first video notice how today, Friday, the strongest NW wind is  over the Southern California offshore waters. Then note how the windy zone expands towards the Bay Area Saturday.

Then in the second video you can see how a slight movement of the North Pacific High way out in the pacific can shift the focus of the North Pacific High’s surface NW winds.NPHnwWindSlideUPCoast

Posted in Los Angeles, San Diego, San Francisco