WTF…. the North Pacific High with a former hurricane in its center.

If the climate is not changing then something is…….

by Mike Godsey, mike@iwindsurf.com

NPHHurricaneMiddle

Posted in Los Angeles, San Diego, San Francisco

Ex-hurricane Marie distorts the North Pacific High

NPHvsMarie

Posted in Los Angeles, San Diego, San Francisco

Degrees of Wind Direction along South Carolina: Onshore vs. Offshore

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By WeatherFlow meteorologist Shea Gibson

For Coastal South Carolina:

As we get into the cooler months of fall and winter, we start to see more NE events unfold along the SE Region as colder High pressures to the north wedge down behind cold fronts that push through. For NE winds, as a cardinal direction we use in forecasting, we see variances in NNE <–> ENE which have a significant impact on SE’erly facing beaches along the South Carolina Coast.  This can also be said for the directions of SW<–>W in some instances.  For the many water sports enthusiasts who use shorelines as a safety net, it is important to know if a wind field is offshore or onshore – or more specifically side-on, side-side or side-off for many intents and purposes. For this we can use what is called a “Wind Rose”, which is derived from compass readings and can use azimuths  (degrees of direction) for many purposes.  As in a circle with 360°, wind directions can be gauged on these “azimuths” to find out exact degrees of flow.

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The four main “cardinal directions” of a compass rose are North, East, South and West.  These directions can be broken down further into inter-cardinal or “ordinal” directions of NE, SE, SW, and NW.  Even further broken down we have the “secondary inter-cardinal directions”, which are NNE/ENE, ESE/SSE, SSW/WSW, and WNW/NNW.  Here is a typical compass rose and the table of all 16 (cardinal) points with their azimuths listed:

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Some of the Wind Roses have a proper sailing term of “b” in the verbiage, which means “by”…so for example if you see NEbE – that means NorthEast by East – or just a hair below NE leaning towards ENE.  Many European mariners use a 32 point “Mariner’s Compass” for exactness in their navigational purposes– and some even still use the “Principal Winds” to go with them http://en.wikipedia.org/wiki/Classical_compass_winds ; however, meteorologists tend to stick with the main 16 in the above two pictures. Here are a couple of examples of a Mariner’s Compass:

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Along the Charleston coast during NE winds, the outer barrier island beaches that face southeasterly directions (such as Isle of Palms, Sullivan’s Island and Folly Beach) currently appear to need at least a ~65° ENE angle of wind in order to become at least side-side to side-on direction for most locales given the most recent angles of the beaches themselves… with perhaps northeastern IOP needing a slightly higher degree of angle to 70°+.  Otherwise, winds become land shadowed and sensors are not able to get true readings. Around the northern “drumstick” tips of these islands, we see that lesser degrees of angle are needed to become onshore and possibly even NNW/NW to some locales, but the further out one goes the greater chance for being pulled out to sea by heavier winds in the event of something going wrong – especially on an outgoing tide.  The tide definitely should be considered as surface winds coupled with surface currents can make for a deadly combination on the outgoing tides.   Rip currents along beaches and along rounded tips where eddying occurs can also enhanced by both coupled and oppositional currents.  Adversely, on the opposite end of the spectrum, we’re looking at Westerlies going offshore after passing the ~240°-245° mark.  

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Folly Pier even at NE @ 38° is still side-off

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You can see how the ENE lean really makes a big difference along local sensors. Here is a graph at the Folly Beach Pier from August 24th, where you can clearly see the higher speeds as winds go more onshore between 6-10pm and fall quickly as winds become more offshore around 11pm.

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 And here is one from the Isle Of Palms pier on August 26, 2014 per an update to this blog since such a perfect example presented itself:

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Here are some local Wind Roses for the Charleston area. The wind roses were created and shared by Charleston local Tom DeMille by using compass overlays on Google maps. These are a great example of tools to use that can help when watching azimuths for safety along just about any coastline.

CHARLESTON, SC

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Folly Beach/ Morris Island / Charleston Harbor Entrance

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North end of Folly / South end Morris Island

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South end of Folly Island/ Folly River / Stono Inlet / Bird Key

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Sullivan’s Island / South End of Isle Of Palms

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Seabrook Island / Deveaux Bank / Edisto River Entrance

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Posted in Coastal South Carolina

Eddy winds creating SW flow for the Bay Area…

End up being sucked into Hurricane MarieGolden GateEddyHurricane

by Mike Godsey, mike@iwindsurf.com

Are you are a coast or Coyote and 3rd. Ave. sailor hating those SW eddy winds? Want to get even?

Watch this video from 10AM today to see those dratted eddy winds get chew up by Hurricane Marie.

Unfortunately the hurricane helps distort the North Pacific High making it’s normally NW winds more N to NNE which acts to maintain the eddy that has plagued the coast much of this summer.

Posted in San Francisco

North Pacific High battered by tropical storms

Well, the NW wind made a weak cameo appearance today as forecast. But if SW flow is not to your taste don’t get your hopes up for tomorrow. NPHvsTropicalStorms

This summer the North Pacific High’s surface NW winds have been battered by Cut-Off Lows, Golden Gate eddies, Upper troughs and most recently by huge 850 mb eddies at 5000 feet.

But tomorrow a covey of 4 tropical storms west of Baja divert much of the North Pacific High’s surface NW winds away from the Bay Area.

Posted in San Francisco

Surface eddy and 850mb low double team the Bay Area….

So southerly flow continues.

by Mike Godsey, mike@iwindsurf.com

If you are a coast sailor or kiter or your home waters are adversely impacted by SW flow you are probably wondering what is going on this summer.
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And the forecast geek talk about counter-clockwise spinning surface eddies and 850mb lows over the Bay Area does not help much.

So below is a split screen animation that shows the 2 causes of today’s southerly flow. On LEFT you can see the surface eddy that is created by the North Pacific High perversely having NORTH wind west of the ocean buoys. On the RIGHT  you can see the model output of the low pressure area centered right over the Bay Area.

Together these features maintain southerly flow most of the day today. However I am forecasting both of these critters to die tomorrow so the Waddell, Crissy, Coyote & 3rd. winds should improve Friday.

Posted in San Francisco

Gorge: cut-Off Low slides down the California coast so….

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Big winds likely for the Gorge starting tomorrow.GorgeBigWinds Cut-Off Low2

by Mike Godsey, mike@iwindsurf.com

Video #1 Winds at ≈ 18,000 ft.

Today, Monday August 18: The Gorge has only low teen winds today . Looking at the video find the Gorge and notice the counter-clockwise spinning winds of the Cut-Off Low over Northern California. Then note the powerful WSW winds  north of the Gorge. There winds are from an upper trough over 3 miles aloft.

Video #2 & 3 Winds at ≈ 18,000 ft.

Tuesday August 19: Notice how overnight the Cut-Off Low you saw in the first video has dropped southward and is south of the S. F. Bay Area. This allow the powerful winds of the upper trough to come over the Gorge and the upper trough settles over the Pacific Northwest. 

 The Cut-Off Low  California should steer the upper trough over us. This:

a. enhances surface low pressure in the Columbia Basin.

b. Shoves the heat producing & gradient spoiling upper high eastward

c. Nudges the North Pacific High closer to the coast,

d. Increases brings clouds overhead and

e. Adds a major gust factor as the strong upper winds transfer momentum to the surface winds.

If all of this adds ups in the  wind equation parts to the Gorge should see upper 20′s wind tomorrow with gusts into the 30′s.

But remember…. this forecast all hinges on an unpredictable Cut-Off Low behaving!!!

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Posted in Columbia River Gorge

Cut-Off Low brings woe….

Weak Gorge winds.
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by Mike Godsey, mike@iwindsurf.com

There is an old saying in meteorology: A Cut-Off Low is a weatherman’s woe.
 This is because Cut-Off Lows are very unpredictable and tend to meander around since they are cut off from the main flow of weather. They and there counter-clockwise spinning flow or clouds can disrupt the surface pressure gradient and brings sudden switches from NW to SW flow aloft as the Cut-Off Low wobbles about. 

The imagery below of satellite and model output shows the counter-clockwise clouds and wind of the current Cut-Off Low parked over the Gorge that has brought woe to windsurfers and kiters for several days.

To see where this Cut-Off Low came from check out this blog:

http://blog.weatherflow.com/large-cut-off-low-anchors-off-bay-area/

 

 

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GFS model animation

Posted in Columbia River Gorge

SAL-ty Atlantic: The Saharan Air Layer Part II

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by WeatherFlow meteorologist Shea Gibson

For SAL-ty Atlantic Part I of this series, please see http://wp.me/p4sVyF-4dz

So far, the Atlantic Season has seen two named storms: CAT 2 Hurricane Arthur -  which formed off the SE coast and made landfall over coastal NC… and Hurricane Bertha, which barely stumbled out the ITCZ (Intertropical Convergence Zone) gasping for moisture, crossed the Lesser Antilles/Puerto Rico/Dominican Republic/ Turks and Caicos, and curved up towards the SE coast and hooked away from land as it finally bombed out as a Category 1 and said its goodbye.

The ITCZ has continued to be heavily impacted this year by the Saharan Air Layer (or “SAL”), which sends dust off the western African coast to lower and mid levels of the atmosphere. This dry, dusty more stable air rides just along the northern ITCZ boundary and has been the downfall of many tropical waves coming off the coast by weakening cyclogenesis, or dissipating formation of convective storms around the centers of Low pressures.  Moisture contents have been low for feeding into potential candidates. This coupled with a few areas of mid/upper level shearing environments and below normal Tropical Atlantic sea surface temps, we just aren’t seeing much activity this year…yet.

This was taken by NASA (Earth Observatory) using Aqua MODIS on June 24, 2014 just to give you an overhead perspective of how far out the dust plume reaches – all the way to the South America, Caribbean and the Bahamas – and even into some parts of lower USA.  http://earthobservatory.nasa.gov/IOTD/view.php?id=83966

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You can view a nice animation of plumage here: http://youtu.be/F3Q8Sh2AjPo

Here is a neat little gif from the end of July to first couple of days into August , where you can see how the dust layer quickly suppresses clouding and convection:

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So as are getting more into the Cape Verde Season, we have seen a couple of tropical waves look very impressive coming off the African coast, but only to be blinked out of existence by wave after wave of dry air being swept off of Africa and bulging down from the north.

August 12:

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August 14:

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The most current wave looks to head NW directly into the SAL, so the NHC is giving it a very low 10% over the next 48hrs and 10% in the next 5 days.

All-in-all, we are waiting to see if the SAL weakens and/or lifts a bit farther north of the ITCZ so that some of these waves don’t have that initial stream of dry air to work through.  Even though next week is supposedly the talk right now with many meteorologists, the NHC seems fairly confident that we have an increased chance of a below-normal season at hand for the most part (updated August 7th).  http://www.noaanews.noaa.gov/stories2014/20140807_hurricaneoutlook_atlantic_update.html

Stay tuned for the next SAL-ty Atlantic part of this series as we get deeper into the peak season.

Posted in Coastal South Carolina

Large Cut-Off Low anchors off Bay Area…

Watch this Cut-Off Low trigger an atypical mild marine surge.Cut-Off Lowwinds.jpg

by Mike Godsey, mike@iwindsurf.com

As expected this Cut-Off Low triggered marine surge has been mild and very atypical. But overall the marine surge has been even weaker than expected. Anytime a Cut-Off Low is in the wind equation things get unpredictable.

Today, as Claire forecast, the SW marine surge flow is very modest. Let’s take a look at some imagery to see why this is happening.

Cut-Off LowToday.gifIn the first image we are seeing the GFS model output. Notice that there are very strong NNW winds from the North Pacific High far to the west. But the Cut-Off Low at about 18,000 ft. has induced a counter-clockwise low pressure at surface to our west. This is where our SW flow is coming from. But the low pressure is so far to the west that only a hint of those winds are reaching inside the Bay Area.

The second image shows the actual Cut-Off Low at about 18,000 ft. Note how powerful the winds are way above the Bay Area. You might expect that all that wind would stir up our surface wind. But today there is a strong inversion at about 2000 ft. so the cool dense surface air is barely moved by all that wind aloft.

The third image is an animation of the last 24 hours of the satellite imagery of the Bay Area. The long pause you see in the video is the END of the video. At the start of the video you see the Cut-Off Low stirring the surface clouds in a counter-clockwise fashion. Then the image goes gray as the sun went down last night. Then notice how the SW winds induced by the Cut-Off Low shove the marine layer clouds into the Bay Area. Then the image goes bright at dawn today and you can see the impact of the Cut-Off Low more clearly.

There is a corny old saying in meteorology. “Cut-Off Lows are a weatherman’s woe” And if the Cut-Off Low you see in this imagery were to suddenly shift eastward towards the Bay Area we could abruptly see Rio Daze this afternoon.

Posted in San Francisco