Whence the North Pacific High

Where were the NW winds yesterday and why are they more likely today

by Mike Godsey, mike@iwindsurf.com

I am glad I was not forecasting yesterday April 22. The night before Mark forecast solid NW winds building along the coast. And Ben, Wednesday morning, was going crazy trying to figure out if the SW flow would finally end and if the NW wind would actually arrive. As you probably noticed yesterday there was only a hint of NW and Berkeley got solid wind from the continued WSW flow. And it was frustrating to see the ocean buoys ramp up from the NW late in the day  but that wind never really arrived in the Bay Area. So Ben had to issue one of those dreaded “Backcasts”.

So why was it so difficult to make a correct forecast. If you watched ocean buoys or the local models yesterday it seemed so easy to do a forecast. After all there was strong NNW wind 10 miles west of the Bay Area and all a forecaster had to do is predict when those winds would turn more NW which would bring them to the Bay Area beaches.NPHmovesWindNNWtoNW

The problem is that the wind direction of the North Pacific High’s winds is determined by events hundreds or even a thousand miles away. Basically if the North Pacific High pushes a ridge into far Northern California or the Pacific Northwest the winds off the Bay Area go NNW and rush parallel to the coast. So it is much harder for them to curve into the gaps in the coast range.

To visualize all of this and why it makes forecasting difficult lets look at this animation. First note the center of the North Pacific High yesterday April 22. Then look at the winds near the Bay Area on that day. Note that they are NNW and notice the eddy just west of the Golden Gate creating WSW flow through the Bay. Now watch the animation as the center of the North Pacific High drops southward today April 23. Note how the winds turn more NW along the coast and how the eddy disappears. Also notice how the NW wind penetrate deep into the Bay Area.

And what made the center of the North Pacific High moved southward? Basically a storm system to the north is pushing the North Pacific High to the south which brings the NW wind closer to the Bay Area cost.

Of course getting this forecast NW wind to the bay hinges on the pressure gradient climbing this afternoon. That hinges on good clearing today. Hence the big HEDGE in the forecast.

Posted in Los Angeles, San Diego, San Francisco

Marine Layering or lack there of busts 1st forecast.

OBX Cranks 3/26/15 Instead Of Disappointing

Tim Kent

4/23/15

  • 1st East Coast shift back in the forecaster chair or in my case couch-no excuses.
  • Pretty straightforward synoptic scenario with a Warm front lifting back up the coast in advance of approaching Cold front.

 

 

Screen Shot 2015-04-20 at 8.55.05 AM

  • The suggestion for most of the coast was for warmish moist S’rlys to fill in wherever Marine Layering was not an issue.
  • For many well exposed S facers up and down the East Coast marine layering WAS an issue and the forecast was unfolding nicely.

 

Screen Shot 2015-04-23 at 7.06.34 AM

  • Data from Neds Point suggesting typical marine layering graph with ups and downs and struggling to pass 10kts until winds veer more shore parallel late.

Thinking I am like really smart and got this forecast thing all figured out I merrily power through my forecasts Wednesday PM with this being my OBX 7PM update…

Screen Shot 2015-03-26 at 6.34.52 AM

 

  • Important to note here is that these tables are ~ 10kts lower than much of the model suite.  I figure that I am smarter than they are and am gonna score a good forecast while all other sources get busted with much too strong of flow.

For the 7AM update I note that most areas are going according to plan but when I get to the OBX I am shocked  to see this:

Screen Shot 2015-03-26 at 6.28.47 AM

  • Here you can plainly see ALL of the guidance suggesting solid S’rlys
  • I have to scramble to get back in line and post a 7AM update that is much more aggressive.

Screen Shot 2015-03-26 at 6.35.57 AM

 

 

All scrambling and Mr. Smarty Pants aside lets take a closer look into the factors that led me to be so confident that Marine Layering would sap the S’rly flow for the OBX and so many other zones.

COLD WATER

Screen Shot 2015-04-20 at 9.05.00 AM

 

WARM/MOIST AIR

Screen Shot 2015-04-20 at 8.55.05 AM

 

LACK OF STRONG MID/UPPER FORCING

Screen Shot 2015-04-20 at 9.03.42 AM

 

NON SHORE PARALLEL FLOW

Screen Shot 2015-03-26 at 6.27.00 AM

 

So in spite of all the whys….why not??? Uncertainty lingers….

  • Looks like a slightly stronger gradient developed over and just offshore of the OBX.
  • The directions were more shore parallel than expected early on.
  • The OBX has a lot of differential temperature boundaries that aide in mixing regardless of water temps on the beach.

Other thoughts and ideas welcome!

Posted in Cape Cod

Drawing a line in the water.

3-6-15 beachfog

By WeatherFlow meteorologist Shea Gibson.

Every spring during the warm surging of Southerly winds, forecasters along the coastal SE Region are plagued with quite a dilemma. It’s called “marine layering”.  This presents itself in subtle ways –  such as a thin haze just over the top of the water …or not-so-subtle ways such as visible coastal blanketing of sea fog that meanders in-and-out of the immediate beaches during the day…and creeps into the harbor and inland at night.  Sometimes it blankets the entire coast and sticks all day. This is the result of our cooler Atlantic shelf waters remaining cold as warmer air starts to lift into the SE Region during the seasonal shift. This much warmer air creates a dense cooler layer that gets trapped at the surface and can be further thickened by hotter air pumping into the region. The wider the difference between higher air temps and the cooler water temps, the thicker the layer.  They can even increase their own additional humidity levels through evaporative effects… even with drier and warmer air over the region.

What this means for winds…is what we refer to as “decoupling”…or where the winds simply cannot elevate near the surface due to the cool stable air firmly in place.  When winds blow in off the ocean, there is only cool air backing them, which means that there isn’t a good “surface mix”. We need warmer and dryer air to fill in over the water in order for winds to increase as the air becomes more unstable. If we have warmer land masses upwind, we start to see those winds mix downwind, which explains why it’s super windy in the Charleston Harbor/upriver/inland …and very light at the beaches.  The resulting air temperatures becomes a HUGE factor as we can see up to 20-25 degrees of difference at times from the Chas Airport (for e.g.) to Isle of Palms.

Ok..so let’s take a look at March 4, 2015  where we saw a significant marine layering event unfold.  Below is an edited surface map from 3/4/15 showing a stationary boundary starting to lift inland of the coast and a cold front approaching.  Atlantic High pressure provided a healthy Southerly flow and our Sea Breeze process was on track to bring winds up along the beaches. At least…that’s what the computer models thought.  Here was my local forecast:

WEDNESDAY FORECAST 3/4/15:  Low confidence for beaches to see increases past 12/13kts today….The nearly stationary boundary is rippling over us now and slowly lifting as a warm front out of the area. Air temps are expected to warm up possibly up into the low 70’s, which could be problematic for winds to increase along the cooler shelf waters of the immediate beaches still hanging around 48°.  As the sun comes up and temps climb, we’ll start to see if marine layering presents the complication as the water surface stabilizes and possible fog blankets the coastline. Just inside the harbor mouth and upriver/ inland, we’re likely to have a stronger yet somewhat turbulent flow developing 15-20kts with higher periods during peak heating. Upon looking over the ADDS (aviation) forecast for 2:00pm today (1900UTC) for an idea of what the low level jets are doing, there is a 40kt projection at 3000ft and 40-50kts at 6000ft…which basically means that the winds just aloft are healthy enough to elevate along the beaches should a surface mix be allowed. Abundant sunshine coupled with much dryer air will be key for the mix. Should the cooler waters generate their own higher humidity levels/increased marine boundary layers with air temps being significantly higher, thin to medium fog blanketing may stick along the immediate coast to cap wind speeds at 10-12kts with a brief “punch” or two past it. Based on historical observations, the delineation line of this “fog curtain” between the beaches and the harbor could be very fine – as much as 100-200 yards wide where we see sunshine and 15+kts on one side… with fog and 7-10kts just on the other side.

3-4-15

Okay so what happened?

This happened at Sullivan’s Island overlooking Breach Inlet towards Isle of Palms…a thick blanket enveloped the beaches, but cleared away just on the backside of the barrier islands over the ICW.  Why? Because land heating effects dried the air and helped clear the fog out to the north.

3-6-15 beachfog

 

Here you can clearly see the dryer air along the backside of Sullivan’s Island all the way up to Isle of Palms..where the fogging creeps back in between wider coastal gaps to the north if you look on the horizon.

3-4-15 backside islands

So what were the winds doing? First let’s keep in mind that the Sea Surface Temperature was still a chilly 48° – 50°.

Here is the Isle of Palms Pier graph and info- the winds were SW and blipped up into the mid teens during areas of temporary clearing, but stayed down at or neat 10kts for the most part as fogging won out. Notice the high air temp – which only reached 57° at 10:40am and stayed cooler all day between 50°-57° with the cool onshore flow.  Air temps at the airport reached 80°. That’s a 23°- 30° difference! 

3-4-15 DS graph

Here’ the harbor–where winds cranked up to a rather turbulent flow and actually warmed to 67° with help from land masses to the south.

3-4-15harbor

And the airport…proof in the pudding for much warmer air temps topping at 80° and higher wind speeds (higher turbulence as well).

3-4-15airport

 

DRAWING THE LINE IN THE WATER

OK…so what was going on in the harbor vs the beaches?  Here was the early morning shot where you can already see the difference.  The physical observation I put to the test on the water was done kiteboarding in the mid/late afternoon hours during the higher peaking of speeds- and the purpose was to find out how wide this line of demarcation really was. Launching from Fort Moultrie on Sullivan’s Island just inside the harbor and heading east towards the visible curtain, I noticed that winds started to cut off wherever the land mass to the south stopped feeding the warmer air across the harbor. This line was literally 50-100 yards wide where winds fell off drastically to a point where turning back the opposite direction was the only choice to “keep the wind in the sail” so to speak. This was tested several times and I found quite a bit of turbulence in the overall wind field…and less turbulence the further upwind I went across the harbor towards the source of the instability.

3-4-15 line

By 8:55am things start to increase with the sun heating things up.

3-4-15 DS surface

So let’s look at another “line in the water”…April 9th showed a period of marine layering where water temps rose to mid 60’s…but still showed decoupling. This visible layer was very thin as a result. However, the line was still there.  You can clearly see the land heating effects.  Most of James Island is rural to suburban residential to commercial, which actually increases radiation (heat) over that land as well to add to speeds.  

4-9-10 MBL

 

10959355_10206331668154422_3809726423229044271_n

10645309_10206331668674435_1956076265944688139_n

 

THEORY about tidal effects: Tidal flushes where there is a 6-7ft swing should have warm pluming effects to the harbor waters all the way to the mouth as the recently warmed fresher water from inland marches/estuaries mixes into the higher body of salinity heading into the ocean.  This would keep fogging just outside the harbor mouth. Adversely, cooler water water pushing into the coastal breaks would likely carry the cooler more stable water and its coupled fogging just inside the harbor to a point.  These have been observed to a point, but not enough to say this is conclusive evidence.

3-4-15 tideout

4-4-15 tide out

Here is a stratocumulus fog bank being lifted inland and edged out by dryer air. This dissipated in minutes.

20150309_133449

 

Conclusion: The correction to this issue comes when water temperatures start pushing into the mid 70’s and higher. Warmer water helps create a better surface mix for the local Sea Breezes as we get into the swing of our hot season here. Looking at the SST animated chart from April 1st to April 21st…water temps are rising fast. Already right around 70°!

SST

 

Cheers,

WeatherFlow, Inc.

Posted in Coastal South Carolina

Gorge & Sherman Island blast. Southern California winds are limp.

Gorge&Sherman

Rough Draft

Yea, you read about upper ridges and upper troughs
all time in the forecast.
Let’s see them in action!

by Mike Godsey, mike@iwindsurf.com

Check it out! The top image songs gusty winds in the mid 20’s range all day at Sherman Island. And the inset shows the wild gusts on the hilltops around the bay.

Now looks at Maryhill in the eastern Gorge. Note the abrupt ramp up to the 20’s and the second ramp up into the 30’s. Again notice the powerful gusts on the ridge tops in the inset of hill top sensor along the Gorge.

What triggered these winds? For both venues local pressure gradients played the major role in the strong wind but these wind were jazzed up by that arrival of an upper trough at ≈ 18,000 ft.

Let’s analyze the Gorge first.

The last several days an upper ridge has been over the Gorge bringing on unseasonably warm weather and blue skies.  Then last night that upper ridge at ≈ 18,000 ft. moved eastward. Looking at the animation below you find the upper ridge that has moved east of the Gorge. The upper ridge is the northward extension of the upper level winds you see east of Oregon. The air within the upper ridge is relatively warm so Idaho and Utah are seeing warm weather today.

Now look east of the Oregon coast and you can see an upper trough at ≈ 18,000 ft. heading towards the Gorge. The air within this upper trough is relative cool and if you live in the Gorge you noticed it was much cooler today than yesterday when the upper  ridge was over us.

As the upper trough moves towards the Gorge powerfulUpperRidge-Trough-CutOFF  SW then WSW then W winds come over the Gorge. As this wind hits the Cascades these winds transfer some momentum to the lower winds which in turn stir the surface winds adding a gust factor and giving the wind a more SW cant. Since the western Gorge is close to the Cascades the wind is more turbulent especially west of Dougs so windsurfers and kiters are heading out east today.

Things are more complex in the Bay Area. You can see that the SW winds at ≈ 18,000 ft. are much weaker over the Bay Area and with warmer water to the south this SW flow and lower pressure aloft allows the marine layer to deepen so much of the Bay Area was buried in fog today. Plus all the topography next to the launch sites keeps the turbulent wind flow from reading the surface at most sites. But Sherman is further from the ocean and there is very low topography to the W and WSW. So the transfer of momentum is unimpeded at Sherman Island. Again most of the wind is from the pressure gradient to Sacramento and especially Redding. But the flow aloft does all a major gust factor to the normally steady Sherman winds.

And how about Southern California? Look at the bottom of the animation and you can see a Cut-Off Low has pinched off from the upper trough. Cut-Off Lows, if they are directly over you, are wind killers so not much wind in Southern California today.

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

Clouding the Forecasting

by Meteorologist Kerry Anderson

Each day when we create a forecast for winds we use many different tools, surface and upper observations, numerical forecasts models, soundings, wind profilers to name a few.  For today’s forecast the most important tools have been the upper air soundings and satellite pictures because in order to determine how strong the winds will be at the beaches this afternoon we needed to know how much insolation the clouds would block.  If the inland valleys don’t heat up there is little thermal gradient and then less support for the afternoon sea breezes.

At midday the visible satellite picture (Fig 1) showed clearly that the marine layer stratus was well developed and pushed right up against the mountains.  Marine layer clouds develop when the ocean surface is cooler than the air above.  That happens frequently in this area because of the cold ocean currents that flow into the area.

Upper Low 4.21.2015

 

Figure 1 Visible Satellite picture for 21 April 2015 for Southern California.  You can clearly see the marine stratus that have banked up against the mountains  keeping the Los Angeles basin socked in with clouds.  Also notice the high level clouds coming off the Santa Barbara coastline spinning around an upper level low and the thunderstorms building over the San Jacinto and San Bernadino Mountains

 

You may have noticed in the forecast today that we called these clouds marine stratus rather than marine layer clouds.  They have that distinction because the base of these clouds is higher than the usual marine layer clouds.  An upper level low in the area is giving the air some lift.  When the air is lifted to the point that it condenses a cloud will form.  We call that the Lifted Condensation Level (LCL).  That level is calculated and noted on a sounding ( a plot of the temperature, moisture and wind profile for a location).  You can see the plot from San Diego this morning in Fig 2.  It clearly shows why these clouds developed. The LCL is quite high at about 4000 feet, so we don’t have fog and drizzle but a higher based stratus deck that has pushed up to the mountains.

 

Sounding San Diego 4.21.2015

 

Posted in Los Angeles, San Diego

Somethings happening here. What it is ain’t exactly clear:

Or as Buffalo Springfield once said: “Is April is the new June?”

by Mike Godsey, mike@iwindsurf.comAprilisNewJune

Look at the first bunch of images taken this morning and you can see that everything looks normal…. for June. I mean, what is going on? Deep fog burying the entire California coast and well inland. Sherman Island blowing in the low 20’s. An huge eddy west of the Golden Gate throwing SW flow into the Bay Area when there should be spring NW wind. Has Global Weirdness fully arrived?  No! Instead several fairly common spring variables that create weak SW flow along the Northern California coast just happened to occur at the same time and the combo a very early season marine surge such as we normally see in summer.

Let’s analyze each of these one at a time to see help Buffalo Springfield and rest of us get the picture exactly clear.

In this first animation you can see the NNW to NNW winds of the North Pacific High today. As you know for almost a week the North Pacific High has held a ridge into the Pacific Northwest giving the Gorge summer like weather. And that ridge has caused the Bay Area’s normal NW wind to pull away from our coast and turn HugeEddyPart1NNW. You can see this on the far LEFT of the image. When the winds of the NPH are in this position we frequently get a weak eddy west of the Golden Gate.  Looking at the middle of the image note the huge eddy west of the Bay Area and and how the resulting SW flow is focused at Sherman Island. But also note how WEAK the eddy winds are outside of the Golden Gate. So at most they could only add AprilML& eddya few knots to the weak SW flow. And the eddy surely could not produce the massive fog bank you see in the top image burying the entire California coast.

So to get rest of the answer let’s of up to almost 5000 feet and check out the winds there. Notice the counter-clockwise winds from the upper level disturbance Ben mentioned in his forecast.

This flow slightly impacts the surface air bringing moist warm air from offshore Southern California towards the Central and Northern California coast. As this warm moist air encounters the cooler upwelled waters to the north the water vapor condenses and forms fog. Hence all the fog along the California coast.

Ok! So we got lots of fog and weak SW flow from the eddy but where is all of strong SW surface wind coming from that is hitting Sherman Island this morning?

Check out the last image. When the North Pacific High tilts into the Pacific Northwest it pulls away from the coast. And this allows theCentral Valley thermal low in the Redding area to expand over the far Northern California coast. So now we have low pressure directly north of the Bay Area. Combine that with a moderate pressure gradient to Sacramento to weak SW eddy flow and you have strong LobeLPSW flow at Sherman Island. And later this afternoon as the fog retreats that pressure gradient will move closer to the coast and the central bay should see solid winds.

Posted in Los Angeles, San Diego, San Francisco

Geek talk: “the Central Valley thermal low expands over the coast”.

What does this mean and why will the winds be weak today?

by Mike Godsey, mike@iwindsurf.com

NNW&NE

Something is really weird with the wind this morning. Looking at the Bay Area wind graph at 9AM you are seeing mostly NE winds. And looking at the model animation above you can see the ocean winds are NNW rather than NW out at the ocean buoys and NE over the bay. Also notice the purple area in the Central Valley that represents high pressure (not the typical low pressure) and instead there is low pressure just west of the Golden Gate.ValleyLowExpandShrinks

Let’s analyze this set up to see what caused it and why most Bay Area sites will only see weak wind today.

Looking at the wind graph, #1 below you can see this unusual wind pattern. Next notice how image #3 shows the SFO-SAC pressure gradient  was actually negative at dawn today while the Redding pressure gradient was strongly reversed meaning there was high pressure there hence NNE to NE winds towards the Bay Area.

The critical image is #4. Notice how the isobars of the Central Valley thermal low have expanded west of the Bay Area. This is creating the low pressure you see at the top of the page and the NE winds. There NE winds tend to push the NW ocean wind away from the coast as you can also see in the top image and they tend to keep the low pressure west of the Golden Gate.

Next notice in image #5  how this afternoon the isobars of the Central Valley thermal low retreat eastward towards the East Bay hills Notice in image #2 that as this retreat happens the SFO-SAC pressure gradient inches upward. However most of the pressure gradient is focused from Treasure Island westward. That is why I am forecasting weak winds for the East Bay  and Sherman Island.ValleyLowexpandsOverCoast

In the final animation you can see the dance the valley low performs as we go from early morning to late afternoon.

Of course the big question what caused the Central Valley thermal low to lunger over the coast. And the short answer to that when the North Pacific High pushed a ridge into the Pacific Northwest the resulting NE flow causes the valley low pressure to drift westward and the Bay Area only sees mild winds.

Posted in San Francisco

Battle between the NPH’s NNW and NNE winds…

The Bay wins today but mostly loses tomorrow.RidgeNPH

While the Gorge sees beautiful warm weather but no wind.

by Mike Godsey, mike@iwindsurf.com

Typically when the iwindsurf.com forecast mentions a ridge from the NPH and NW ocean winds but NNE winds aloft over the bay only weak winds are forecast for the Bay Area. Today, April 15, should be an exception to that rule.

But first let’s talk about ridges and where the NNE wind come from. Looking a the first image find the NPH. Usually in the spring the NPH is round to oval in shape and spans the waters between California and Hawaii. But often after a period of strong NW wind on the coast this mountain of high pressure air pushes an extension or ridge into far Northern California and even into the Pacific Northwest.

Looking at these isobars you can see this ridge making such an extension. Also notice how as the NPH elongates the isobars show low pressure extending from the Central Valley over the Bay Area.

With low pressure over the bay the SFO-SAC pressure gradient  is very weak as you can see in the modeled pressure gradient chart.

The video in the next image shows the wind flow pattern that develops as the North Pacific High ridge forms.

RidgeVideoFirst notice the clockwise spinning winds of the NPH. Normally this flow creates NW winds along the Northern California coast.

Now check out the ridge from the NPH extending towards Oregon and Washington.

Then notice near the Bay Area how the North Pacific High’s normal surface NW winds turn more NNW when a ridge forms. If you look at the ocean buoys sensors on a day like today you will see that they are NNW.

Can you see how it will be harder for NNW wind to fill into the Bay Area compared to NW wind?

Also looking carefully you can see that there are northerly winds in the Central Valley.

In the next close up video let’s examine those NNW to NNE winds more carefully. Find the Golden Gate in the middle left of the image. and the NNW ocean winds.

 Then look to the north of the Bay Area and see the NNW to NNE flow in the North Bay and Central Valley. Now zoom your
visual image to the San Pablo Bay north of the Central Bay and see how the  this flow will try to keep the NNW wind from curving into the bay.

Most days the combo of the weak SFO-SAC pressure gradient you saw in the top image and the NNW cant of the ocean winds NNEflowkeeps the winds inside the bay weak, late and mostly from Treasure Island westward.

Today however the NW winds are usually strong and there is a chance that at upper teens to weak low 20’s wind will reach at least the Treasure Island to 3rd strip. And I would not rule out some BattleNWvsNNE&NWwinswind reaching Berkeley. Incidentally Sherman Island sees wind in this pattern but it is typically too NNW to be useful. In this bottom image we can see how the models forecast for today. Look carefully and you can see the wind battle as the day progresses.

Basically today the NW wind overcomes the NNE wind and much of the bay sees decent winds.

However tomorrow, Thursday, I expect the ridge to push much further into the Pacific Northwest so the North Pacific High’s winds go even more Northerly, the SFO-SAC pressure gradient  weakens even more and the NNE winds keep most of the NW wind out to see. So we see lighter, later and weaker winds mostly from Treasure Island westward. And the looking at the top image you can see that are almost no isobars along the Gorge so calm and clear there.

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

Gulf Stream surge brings the Cannonballs back early in 2015.

Cannonball Jelly

By WeatherFlow meteorologist Shea Gibson.

Original article from 5/6/14: http://blog.weatherflow.com/cannonball-jellyfish-signify-the-end-of-marine-layering-along-sc-coast/

Last year, we saw the Cannonball Jellyfish arrive as Sea Surface Temperatures (SST’s) climbed into the 70’s at the beginning of May. This year- they arrived earlier- specifically April 11th/12th along a ENE flow from a nearby surge in the Gulf Stream. Other than being a delicacy in Asia and being only allowed to be harvested in southern Georgia, USA, the significance of their arrival along the shore not only has to do with a fairly strong wind event blowing them in… but also has quite a bit to do with wind forecasting as a visual confirmation of water temperatures rising to just at or near 70° (ideally 73.6° for our little friends… give or take a few degrees).

Cannonball Jellyfish5

The Gulf Stream is a south-to-north driven surface current of warm water within a networking of Thermohaline Circulations (global conveyor belts of ocean water).  Surges in fresh water fluxes mixing with surface heat causes eddies, where the current at times meanders west along its northward flow and plumes warmer water outwards towards the coastline.  WeatherFlow Meteorologist and avid offshore fisherman Tim Kent stated “Cannonballs show with that warmish blue green water often and soon after the spade fish and Cobia arrive.  The first Pompano was caught this past weekend around here (near Charleston, SC) which surely signifies that the water is on the way up!”

It looks like this progressive surge in the Gulf Stream has elevated temps a little faster this year to near 70° along the SC Coast as of 4/13/15. This animated gif image spans from March 24 to April 13 of 2015. Surface Temperatures along the Gulf Stream are currently right at 80° – 82°…and the northwestward surge brought coastal temps from the upper 50’s up into the upper 60’s…and still climbing.

SST April 3-24 to 4-13

For forecasters, it is very important to know for winds and how they behave along the beaches.  One issue we deal with is much warmer air temperatures building over our cooler shelf waters during the seasonal shift – which causes marine layering (with frequent fog blanketing over the water) until water temps rise to a level where that doesn’t happen anymore. Cooler waters cause winds to “decouple” or stay capped to more stable lower speeds than what would normally take place on warmer Southerly winds – especially ahead of cold fronts that generally elevate winds ahead of them.  Quite simply…it makes wind forecasting very problematic to get the speeds correct along beaches versus the inland values and other areas where winds “funnel” through between land masses-  such as coastal breaks (harbors, bays, sounds) and/or upriver locations. Here are examples of how this affects the winds:

Marine layer with a blanket of sea fog along Isle of Palms 3/4/15:

20150304_152540 (1)

Here is what was occurring with the winds in the morning, which continued through most of the day (actually built higher in the harbor). It is almost a very clear line that I consider a “line of delineation” where we see near 10kts at the beaches and 14+ knots in the Charleston Harbor:

3-4-15 marine layer

During experiments riding back and forth across it on other days, there is a distinct drop in winds within  a very short distance – perhaps as short as 50-100 yards as you move into the decoupled area.

March 5 showed even higher afternoon results where the decoupling occurs- with 23-27kts SW in the Charleston Harbor and only 11-14kts SW along the beaches:

3-5-15SI1320

As in the original article, we will see Sea Breezing become stronger along beaches as these SST’s continue to climb in conjunction with our seasonal rising warm air temps. With just a few more degrees, our local Sea Breezes that couple with synoptic Southerly winds will allow for better surface mixing and instability, which in turn creates more wind. As a result, forecasters will have a better reading on what speeds are likely to occur along the immediate beaches.

The bottom line is that Cannonball Jellyfish, at least here along SC, are one of those neat environmental visual queues that thermal imaging satellites and all the advanced swathing in the world can’t catch – at least not yet.

Cannonball Jelly

Cheers,

WeatherFlow

 

Posted in Coastal South Carolina

Old North Pacific High crushed into 2 parts by storm system.

But sliver of the NPH keeps modest NW near the Bay

by Mike Godsey, mike@iwindsurf.comNEWnphLowCrushesOLD

This animation is chock full of weather action. First note the massive “new” North Pacific High north of Hawaii and its clockwise spinning winds. Typically this high pressure would be just west of the California coast bringing us strong NW wind. Also note the trade winds this “new” NPH is bringing Hawaii just offshore.

Now find the clockwise spinning winds of the surface storm west of California. Way above this storm is a near Cut-Off Low that is holding the storm relatively stationary. And in this location it has been crushing the “old” North Pacific High against the California coast.

Actually the system has crushed the old North Pacific High into 2 separate parts each with counter-clockwise spinning. Find the Bay Area and then note the part of the NPH to the north and its counter-clockwise spinning. Now look to the south and note the southern section of the old NPH and its counter-clockwise spinning winds.

Now look carefully just west of the Bay Area and you will see a weak sliver of NW wind just west of the Golden Gate and Waddell. Normally this would not impact the winds inside the Bay much but with a moderate pressure gradient this afternoon we should see at least upper teens wind at sites from Treasure Island west.

Posted in Los Angeles, San Diego, San Francisco