Today we had quite thunderous sound with ground shaking reported along much of the Greater Charleston coast and inland areas. Many felt it could have been an earthquake, others a large explosion.
Ok here it is explained…the loud shaking boom we heard today was a sonic boom from jet aircraft offshore breaking the sound barrier. Beaufort Air Station confirmed they had F-18’s out on maneuvers along NC/SC/GA.
ABC News 4 of Charleston reported in their initial article, “Reports of a loud noise along with houses shaking is indicative of a sonic boom generated by an aircraft of some kind. Sonic booms are pressure waves generated as the aircraft exceeds the speed of sound, they are perceived by the people on the ground differently under different atmospheric conditions,” said Dr. Erin Beutel, an associate geology professor at the College of Charleston. “It can also take between 2-60 seconds after the plane passes through for the boom to be heard, and over the ocean, the pressure wave can travel further and be heard by more people than on land.”
The sonic boom was most likely accentuated by an atmospheric inversion above us, where warm air sits above cooler air at the ground. This warm air “cap” usually looks like a varietal of stratus cloud decking and acts as a conductor of sound waves and allows them to travel further inland. The compression of the sound wave between the warm cap inversion and the ground likely amplified its power and resonated through the coastal areas. This morning’s weather balloon sounding shows proof of a strong inversion aloft (where I added the edit in yellow). Visibly noticeable in the sky was in fact a wide stratus cloud blanket.
Here is the normal “Base Reflectivity” radar we typically might use, which shows a spot of what looks like showers pop up just off of Folly Beach (no rains in the area). ProductCourtesy of Wunderground.
Further evidence of chaff that I caught on “radial velocity 0.5°” shows there was jet activity ongoing just off the coast. You can see the elongated anomaly appear just off of Charleston. This is aluminum-coated or metallized glass reflective material that aircraft release to create scatter, thus cloaking the primary target and spreading the signature out to create what appears as multiple bogies. This is an effective counter-measure used against enemy radar for defense.
The first is a Base Reflectivity loop that shows what looks like 3 jets releasing chaff.
And the second radar loop using the Correlation Coefficient, which tracks debris in the air. Paints a much better picture of the one closest to the coast.
So…when you have jets breaking the sound barrier, and a conducting layer allowing extended distances of the sound waves, you get a loud “boom” that may at times feel like an earthquake.
One more piece of evidence is the barometric spike that the College of Charleston picked up in Scranton, SC, which maintains the case for a sonic boom and not an earthquake. Typically, one would feel shaking first before hearing the noise following. Those who lived further away may have felt the energy for longer (one report from Charleston local Rick Rush much further northwest in Awendaw, SC for 3 seconds) due to the sound wave elongating before dispersion ended.
The last picture here shows how this can also happen with thunder from higher elevations of convection/storms (storms that happen higher up off the ground). Brad Panovich – Chief Meteorologist for NBC Charlotte (WCNC-TV), who shows the correlation between thunder and sonic booms for sound wave travel. Thanks for the great visual Brad!
Here’s a great radar loop sequence that shows another occurrence I recorded from November 25, 2013 that shows a clearer example of chaff releases. Moderate NE winds that day helped push it over the coastline.
So how do winds and water affect sound? An interesting fact was that our waters were fairly calm with a very light onshore flow, which also aided in sound amplification. Ever been on the water and you can hear someone from far away as if they are very close?
In the book, Transportation Decision Making: Principles of Project Evaluation and Programming by Kumares C. Sinha, Samuel Labi, they state the following in Chapter 11 (11.2): “Sources of Transportation Noise” – which basically talks about noise propagation:
All in all, we are certainly glad that this was not an earthquake. But it sure does keep us on our toes when it comes to sound waves and the atmosphere.
Until next time – stay safe out there and keep your ears “to the sky”!
In Part I, we discussed the general understanding of how Sea Breezes work. In Part II, we looked at the different classifications of Sea Breezes and how each one works. Now, in Part III, we move on to more advanced parts of the Sea Breeze. We’ll take a look at how it forms, how it affects the coast and the effects it has to areas well inland.
The question still remains…“What does the Sea Breeze look like?”
In this part of the series, I will present the anatomy of what the Sea Breeze and its components would look like if viewing from the side – and how each part of the system works.
Let’s start off by saying that the Sea Breeze System (SBS) is mainly a vertically rotating mesoscale cell – what I like to call the “atmospheric wind wheel”. In some cases as we discussed with the Backdoor Sea Breeze – a vertically oscillating front, but we’ll stick with the main types for this part. ( See Backdoor Sea breezes along the SC Coast for that one )
As a recap, here is another look at how circulation it is viewed from the side:
ONE POINT TO BE MADE for formation of Sea Breezes:
The formation of the Sea Breeze System is initiated by the temperature differences between cooler sea surfaces and the warmer land. As the difference increases during the day, a pressure gradient is produced at low levels, which initiates the sea breeze near Earth’s surface. This is known as the mesoscale Pressure Gradient Force (PGF) that pretty much is the driving mechanism for the system. First we must look at how Sound Waves develop this PGF.
Sound Waves (Compression Waves) – The picture below shows an Eastward propagation, but keep in mind the direction of propagation is inland to the West along the SC coast.
There are 3 theories on how sound waves commence the Pressure Gradient Force :
The “upward” theory…where return flow develops aloft first due to the vertical expansion of warmer air over land. Due to this thermal activity inland, the flow at the surface starts to flow underneath in accordance to return flow falling back to the surface over the sea and nudging flow at the surface from behind to get the wheel going.
The “sideways” theory…where the onshore flow develops first as the air from the sea presses inwards towards the horizontal expansion of the warmer air over land. Return flow aloft then develops in response to the low-level onshore flow pushing inland, warming and eventually rising as thermals.
The “mixed” theory…where the warmer air over land expands both vertically and horizontally, causing the simultaneous development of the surface sea breeze and the return current aloft. In other words, the parts of the wind wheel all start as one unit and expands over time with heat.
I have my own theory for a different initiation of the PFG – where we could assume that a inversion cap (thermal cap), which creates a convective inhibition layer (called CIN), keeps heat trapped at the surface while the entire mix of air expands inland as its own very thin and “squished” version of an entire Sea Breeze Circulation at a near surface level – trapped in an elongating capsule. We could call this a “Micro Breeze”, where it circulates within a much smaller “bubble”. This would explain the initial bursting of Sea Breezing from an overnight inversion that holds nocturnal jetting into the daylight hours. This type of setup would be in association with a solid area of inland troughing or a cold front approach. Past coastal observations show this strong initial bursting fade as abruptly as it came…and then steadily comes back later as the cap breaks and hot moist air is allowed to finally rise freely to create the larger Sea Breeze circulation.
Here is a wind graph from the Fort Sumter Front Range Light in the Charleston Harbor, where we can see the night time inversion burning off and the initial thermally capped Sea Breeze head pushed ashore and through the harbor around 9:00 AM. (In some cases, this can become a small, clear undular bore as the SB head breaks off and propagates inland away from the cooler air behind it.) Afterwards, we can see where the typical Sea Breeze build re-started and progressively increased through the afternoon.
These graphs were from the Fort Sumter Front Range Light in the Charleston Harbor.
Or…could it be that the Sea Breeze front is receding and the head passes through that area just at that time… and then meanders back off the coast to regroup? That’s a question yet to be answered.
On to the next portion where we analyze the structure of the Sea Breeze.
This picture from Reviews of Geophysics: “Sea breeze: Structure, forecasting, and impacts” by authors S.T.K. Miller, B.D. Keim, R.W. Talbot and H. Mao illustrates the breakdown:
Cu = cumulus clouding
1. (SBC) Sea Breeze Circulation is a vertically rotating mesoscale cell – or what I like to call an atmospheric wind wheel. It has onshore flow near Earth’s surface, rising air parcels inland called thermals, and a return flow back out over the ocean to repeat the cycle – which can become faster and faster as the day progresses for the stronger Sea Breezes.
2. (SBF) Sea Breeze Front is the frontal surge of the SBG nudging the SBC onto land and commencing the event. Noticed are changes in air temps, wind directions and relative humidity. The coast tends to dry out, winds are registered along the coastal mesonets during the turn and fair weather or cumulus cloud build-up’s are visible in the sky.
3. (SBH) Sea Breeze Head is right behind the SBF and is the landward forcing mechanism to overtake the air ahead of it. It tends to be very tall in height with a sharp drop-off just along the crest.
4. (KHB’s) Kelvin-Helmholtz Billows are unstable waves that form right behind the head and along the upper boundary of the SBG during peak heating initiations.
5. (CIBL) Convective Internal Boundary Layer is an unstable area just behind the KHB’s and just ahead of the SBG. This area is where the more consistent winds flow horizontally along the surface. Gusty and more turbulent winds exist inland…where these winds lay down as a steady inflow off the ocean.
6. (SBG) Sea Breeze Gravity current is the cooled, moist marine air in the aft area of the SBC that is a product of return flow from High pressure aloft. This is where the faster rate of sinking air from High pressure aloft can cause the SBG to inject or wedge this cool moist air into the CIBL and ultimately further forward for the thermal lifting to take place.
Kelvin Helmholtz instabilities initiate from limited static stability (where low level moisture meets warmer land) and develop turbulent vortices behind the SBH. This creates the Kelvin Helmholtz billows (KHB’s), which grow in height, fall back and disperse along the density interface. Basically, this area of the SBC is very unstable and shows UP’s and DOWN’s at the surface sensors until the front pushes further inland.
Behind the KHB’s is the Convective Internal Boundary Layer …or CIBL. This is where winds develop along the beaches and builds for the day. This area expands as the head and KHB’s press inland. The SBG remains just offshore or just above the CIBL along the beaches during weakening phases …or at times during True Sea Breezing with a weaker synoptic setup.
Meteorologist J.E. Simpson created a shadowgraph laboratory generated gravity current. Pure water is on the left, and slightly salty (denser) water enters from the right. Visible in the photograph are the current’s nose (slightly elevated leading edge), raised head, and trailing Kelvin-Helmholtz billows (as described in text). This is a pretty good idea of what our Sea Breeze would look like as fluids mix – same principle in the atmosphere.
Simpson, J. E., Gravity Currents in the Environment and the Laboratory, 244 pp., Cambridge Univ. Press,New York, 1997.
Here are three other types of gravity current renditions that show alternative variations of the Sea Breezes, where the “floor speed” represents the surface flow and the “opposing flow” is the opposing land breezes/wind aloft (or shear factor).
You can see the last one is a fairly strong setup and the CIBL is more structured with a stronger sustained flow. The SBG has a wider wedge of return flow circulating back in from behind. This one is more likely to break off at the head at the end of its diurnal cycle as its pushes further inland, leaving the rest of it behind to steadily die off.
The Sea Breeze is really a type of a buoyantly driven gravity current. Thus, if we take a “haboob” or a “sand storm”, we can see how this current operates. In short, if we could see a Sea Breeze coming ashore, it would look something like this, but much, much slower in advancement.
And check this one out from Mike Olbinksi and Blaine Coury of AZ as well…
The technical reason why is because they both have the same frontal head shape, KHB’s behind it…and a buoyancy driven gravity current sustaining speeds along the aft circulation. Of course, the back end is not over cooler water for the SBG circulations to remain sustained, but you get the idea.
Forecasting Sea Breezes is a common problem for forecasters along the coast. In order to dedicate time and effort on the main focus, three main elements are to be considered:
Will they occur? (What is the regional setup?)
What will be the main wind direction and speeds? (what type of Sea Breeze are we expecting?)
How far inland will the Sea Breeze front penetrate? (Is the inland troughing setup / Atlantic High setup conducive for a stronger front to push further inland?)
These Sea Breeze fronts have been know to push pretty far inland- upwards of 100 miles in the Southeast at times. The storm lines can become very thick and violent at times, especially when Urban Heating adds to the downwind effects. Most of the time, they will stick within 15-30 miles, where the convergence zone from inland activity keeps it actively fed along that convective line and keeps the front contained closer to the coast. Topography plays into this significantly as upsloping and downsloping factors shift weight with the respective gravitational influences. This explains why storms surge towards the coast in the late afternoon over the flatter lands and never quite make it – rather they get sheared off up top and fan out their higher cumulonimbus stacks out over the ocean with out any storming. This brings up a good point about the convergence zone inland. Sometimes the storms do break through and advance towards the coast. This can be from a couple of reasons…
The Sea Breeze Head (SBH) snaps away from the front and propagates inland as an undular bore – at times for dozens if not hundreds of miles. This can be convectively sparked and seen as an outflow boundary/gust front on radar. Without the leading edge in place any longer, this opens up an almost unrestricted atmospheric path to the ocean.
The Sea Breeze weakens with cooling from strong updrafting and the storm line is able to overtake the area. The resulting Sea Breeze contamination over the coast typically makes it very difficult for the Sea Breeze to recuperate. But, there have been some known times when enough heating was able to help reform the Sea Breeze front and drive back into the coast once again.
Here is a good example where the fronts along Southeast NC and parts of SC/GA showed the Sea Breeze “losing their heads” and propagating inland as gust fronts (likely as an undular bore).
Here’s what is going on here…
Forecasting Sea Breezes is a common problem for forecasters along the coast. In order to dedicate time and effort on the main focus, three main elements are to be considered:
Will they occur? (What is the regional setup?)
What will be the main wind direction and speeds? (what type of Sea Breeze are we expecting?)
How far inland will the Sea Breeze front penetrate? (Is the inland troughing setup / Atlantic High setup conducive for a stronger front to push further inland?)
With the current WeatherFlow mesonet increasing along the SC coast, we are able to “see” these occurrences more and more…and are becoming more equipped for predicting the weaker vs stronger Sea Breezes during the warmer months. We are even finding out that they occur in the winter – including with absence of cold front approach. We are continuing to expand our coastal mesonets in other parts of the country as well, so we hope to find out even more about our fragile land-and-sea environments.
This ends the three part series of the article…but I am expecting that the ever changing science of Sea Breeze forecasting may prompt further investigations. Until then…stay safe and stay alert out there on the water!
SE Region/ East Coast
Well it’s that time of the year for “marine layering” again as water temps have cooled to the upper 60’s to near 70°. I’ve been recording when marine layering starts for the last 2 years in order to further document the initiating time periods. In the 2013, it started on Friday, November 1st. Last year in 2014, it started much earlier on Friday, October 3.
This year we have seen a more progressive marine layering process as water temps have fallen slowly after the October Rain Storm of 2015. Instead of a substantial drop all at once like we have seen the last 2 years, we have seen 3-5 degree drops in two separate occasions with cold air intrusion and more NE/ENE events. From October 1 – October 12, we went from ~79-80° down to ~72/73° and held there until October 15.
From there we can see the trend from October 16 to present day 11/5/2015 in the NASA Sport SST animation, where temps fall to 68/69° and hold.
The thing to remember here is that warm air masses tend to cause decoupling over the cooler, more stable waters. This means that a layer of cooler air hangs over the cooler surface unless warm air is able to penetrate and mix into it for instability (hence…wind). However, some of these air masses ahead of recent cold fronts haven’t been significantly warm and some have, so we’ve seen a mixed variety of surface mixing and decoupling. Higher humidity levels are said to be a large part of the reason for decoupling; however, even with dry air over the coastal region, these layers create their own higher humidity levels at the surface. They are in many cases, their own body of cool air surface pooling.
The actual first signs of marine layering along a SE flow occurred on Saturday, October 10 ahead of a cold front.
Here are a couple of pictures where you can see thin hazing and fogging at a distance. Pics from local H. Mikell Evatt of Charleston, SC.
The stable layer lasted for awhile before the unstable air and storming moved in to clear it out. Winds never got above 10kts until storms kicked (you can see the arrival in the higher “spikes”). Notice in the next 2 pictures the air temperature over the area was around 76 degrees- only about 4-5 degrees higher than the water temp.
Charleston Harbor 10/10/15:
Isle of Palms 10/10/15:
We had one another cold front approach on October 28th as Low pressure from the Gulf lifted to the north. This brought a warm air mass up along and behind a parting warm front. Here is the edited WSI surface map from the day before showing the projected scenario.
This resulted in warmer air temps trying to inundate the coast; however, the cooler waters kept air temps cooler near the beach as a thin marine layer developed. Notice temps nearing 80° inland..and remaining closer to the actual water temp of 69° along the beaches with the SSW onshore flow.
Here is the result…moderate to strong winds develop in the harbor downwind of the land mass where this warmer and drier air allows for mixing at the surface. The overall environmental instability created allows for winds to build over the harbor- especially as low level jetting is involved ahead of frontal activity. But this wind is turbulent and rather unstable itself…showing lots of UP’s and DOWN’s. Notice the beaches are 7-10kts lower in speeds due to the marine boundary layer created from having no warmer drier air mass coming from land. It’s all coming from the ocean.
Graph of the harbor for the day:
Here is a graph of the IOP sensor for the day, which shows UP’s and DOWN’s as winds came up during temperature equalization around 11:00AM, but then struggled and eventually fell as air temps rose inland. Even with the afternoon Sea Breeze coupling and Coriolis effect veering winds SSW–>SW, we still showed marine layering cap speeds at the beaches to low teens.
This continued into the next day ahead of the slow moving front. On October 29, 2015 – local kiteboarder and Air Force pilot Sam Johnson made a physical observation at the beach Station 28.5 of Sullivan’s Island and stated, “The hazing wasn’t really noticeable right at 28.5, but looking towards the Isle of Palms pier (north) or towards the harbor (south), it was definitely present.”
This picture was provided by H. Mikell Evatt on November 2, 2015 at Breach Inlet, which is a coastal break between Isle of Palms and Sullivan’s Island. It shows light fog that has developed along the beaches.
And here is what was going on in the harbor vs. beaches at that time:
So… I’m officially dubbing October 28th as the true day of the start of marine layering for Fall 2015 for the South Carolina coast.
As you can see in the last few pics of the winds, the line seems almost very fine between the higher speeds and the lower speeds…and guess what? It really is almost like drawing a line in the water.
Massive North Pacific High brings NW winds to most of the California
by Mike Godsey
Yep it is mid fall the time of fading winds on the California coast as the North Pacific High shrinks and moves southward away from the Golden State. The time of year when the days are shorter and the temperatures are cooler in the California interior. Late Oct. and especially early November is a time of falling pressure gradients and faint winds.
So on this last day of the 2015 Weatherflow human forecasts why am I forecasting powerful NW winds from most of the Bay Area and Southern California for tomorrow Monday Nov. 2! It is easy to toss around words like “unprecedented” these day but try this one on for size… this is the first time in 25 years I have forecast strong winds from the North Pacific High in the mid fall!
Sure we sometimes have post frontal NW winds in the winter. Those types of brief NW winds occur everywhere in the N. hemisphere after the passage of a cold front. But tomorrows NW winds are coming from a 1800 miles in diameter North Pacific High and that is extremely unusual in mid fall.
Basically in recent years the oceans, especially the Pacific, have been storing excessive heat. This is why most of the west from Canada to Baja had such a mild winter in 2014/15.
So what was the proximal cause of all this ocean warming? In the north pacific much of it
came indirectly from what meteorologist called the RRR, the Ridiculously Resistant Ridge, which held position at ≈ 18,000 ft. over the eastern pacific and western North America much of the winter. This upper ridge shunted most of the storms way north over the west coast while keeping warmer air at the surface. Hence record low snowfalls and warmer temps.
And out in the north pacific fewer storm means the there was little winter mixing of summer warmed surface waters with cooler waters from the depths. This gave rise to the Pacific Heat Blob you see in the very top image.
The Pacific Heat Blob meant unprecedented warm ocean waters for much of the west coast.
And less snow runoff meant unusually warm river waters in the Gorge and major salmon and sturgeon die offs.
The formation of such extremes in the upper level flows like the 2014/15 Ridiculously Resistant Ridge and the long lived 2014/15 upper troughs from the polar vortex that brought crazy cold temps to the east coast have long been predicted to increase by the climate models.
Likewise the abundance of east pacific hurricanes and the amazingly fast build up of Patricia, the strongest east pacific hurricane in history, was based upon this pacific warm up.
Looking at the 2015 image you can see that the major El Nino building fast the pacific is warming even more.
So getting back to topic… the heat in the north pacific and the prolonged hurricane season have both help cause the North Pacific High to maintain its size and strength way into fall. But this time of year lots of storm systems swing towards the west coast and so far there is nothing like the RRR to divert them.
So today the Gorge is getting hit by rain and SW winds while Northern California has an approaching rainy cold front. You can see the cold front in the first animation I have annotated from nullshool.
Note how the weak NW winds of the old NPH have dropped south of the Bay Area. Then find the cold front approaching from the NW. Note the SW relatively warm storm wind. In the area of the cold front there will be rain that should graze parts of the Bay Area. Behind the cold front is what is called post frontal NW winds which we sometimes see after storms in the winter.
Behind this narrow zone of post frontal NW winds is a massive NPH that spans the waters from Maui to Alaska to California to Baja. And the portion of the North Pacific High near California will create strong NW clearing winds Monday. And aloft will be strong NNW winds that could interfere with the surface NW winds.
The challenge will be to get these ocean winds into the Bay and into the Southern California beaches. Both venues have largely lost the pressure gradient to the Central Valley for the Bay Area and the inland valleys and Southern California deserts for Southern California.
However I am seeing hints of a strong pressure gradient to the Great Basin which typically sucks those NW ocean winds inland. This usually means very gusty winds and kiters should use caution.
Shea Gibson, one of our east coast meteorologist, just reminded me that since tomorrows winds are partially post frontal NW winds and partially large scale NW winds from the NPH we will also see the effect of cold air advection that should jazz up the wind a bit. See Shea’s recent blog on this phenomenon:
By WeatherFlow meteorologist Shea Gibson 10/31/2015
Many are well aware that our coastline is very fragile as air masses over warmer land and cooler waters interact with each other. In some cases, we have avenues of acceleration called Sea Breezes as these two air masses work to create a circulation or oscillation of air. There are various types and classifications of these coastal systems, but we’ll pick one in particular that consistently brings winds up to moderate or strong values. This coastal effect is a rather tricky one since it does not operate like a typical Sea Breeze model you have probably heard of. It involves cooler NE/ENE winds wedging down the SC coast and how it interacts with the environmental atmosphere and the warmer land. It’s called the “backdoor Sea Breeze”.
In order to understand how this Sea Breeze works, we must think of how High pressure to the north steers a sinking cool or cold air mass down the coast, and given its relationship to gravity, sinks downward.
Here is a simple diagram that shows the sinking of this air down at an angle due to winds driving it aloft. This is known as the cold air advection process.
Generally speaking, NNE/NE winds along our coast are cooler by nature of where the air is coming from (the north). As the day heats up and land warms, we see the air “bending” or veering as it makes first contact with the warmer land, or usually the barrier island chain. Specifically, many beaches along our coast are affected by this wind field bending phenomena. Heats draws this rushing air inwards over the islands and steers it further inland. This is the point where the air warms, starts the evaporation process, and then rises inland as its buoyancy increases. This is known as the warm air advection process. We can associate these with “thermals” for those who are familiar with the term.
Without strong storming inland in many cases, we do not see a circulation of air. This type of setup is called an “oscillation”, or movement of air down and then up in an accelerated fashion. We can see this mainly as fair weather or cumulus clouds building inland.
Let’s see what this all looks like:
This shows the cumulus builds inland over Charleston, SC where the ocean is to the right roughly ~10 miles. Totally dry towards the ocean.
And in the summer time, these clouds can take on more convective or stormy characteristics. In these occasions, short wave troughs develop as clouding sinks to lower levels and creates convection where warm moist air and cool dry air mix. This intensifies and throws everything off, either squashing the oscillation altogether or scattering directions while causing localized showers or storms. The below picture came from my article on short waves: http://blog.weatherflow.com/what-is-a-short-wave-and-how-can-it-affect-winds/
Since the overall air mass is already sinking (from strong High pressure aloft), something has to give. As the pressure drops (Low pressure), warmer land starts allowing a faster rate of intake than the air is already moving into the coast – like a vertical venturi effect or squeezing of air. The air is then forced upwards as this bit of cooler moisture sinks and creates buoyant instability during warming and evaporation (lifting) inland. In other words, winds are “swooping down” over the beach while accelerating faster as a result of faster air movement from initial land contact to inland, where it swoops back up. The downward swoop would be where the pressure is dropping, so we see that as Low pressure aloft over the immediate coast. Sometimes, it can be kind of like a bottle of Champagne ready to pop as winds start North and slowly clock NNE…NE…and then pop! ENE winds zoom up quickly with the onshore leans. In some cases, we can see upwards of 15-20kts in acceleration within a 5-10 minute period, which catches many off-guard.
Here is a wind graph from April 21, 2013, where speeds exploded upwards once the direction leaned onshore. That was almost a 15 kt jump in averages within a 5 minute span!
This activity attracts nearby troughing from remnant offshore frontal boundaries like a magnet from afar at times… and can help to increase the local gradient as High pressure interacts with the newly developing coastal trough. You can see these as stratus cloud forms or some mid level type of clouding coming in from the ocean.
Check the following pictures where you can clearly see that thin layer of clouding/troughing lingering offshore (likely out over the warmer Gulf Stream that continues to feed it)..and the resulting directions that occur:
Here’s from about 20 miles inland looking toward the sea across the Ravenel Bridge in Charleston, SC on October 19, 2015 at 11:40AM
And the overhead shot from that day:
And the next day from Sullivan’s Island on October 20, 2015 at 3:45 PM – you can see the troughing offshore on the horizon.
Some of the additional accelerative effects could be due to the open body of water to our north with an exposed land mass that all helps to create a “micro breeze” that quickly settles back down over Bulls Bay and rushes south. This might also explain how Charleston in particular sees higher speeds than most other beaches from Cape Island down through Georgia.
SO HOW DOES THIS WORK ALONG our beaches and do we know any details of what to expect? The answer lies in actual observations while riding on the water and from local sensors, we can see what occurs along our fragile coastline. Believe it or not you can gather LOTS of information while kiteboarding on the water. I find the kite’s physical tension coupled with the harness attached to the body provides very valuable information for how the winds consistently or inconsistently behave. Having the freedom to explore the coast broadens this knowledge. I’m sure many other kiteboarders may agree that what little topography we have along the beaches has a lot to do with what the winds are doing, and so do entire open stretches of beaches and coastal breaks or pools of water upwind.
We see that exposed sandbars help with accelerations in what we experience called “Wind Rivers” offshore and near the beach. To this day, there is no scientific support for this term, but it does exist during these periods of winds. On several occasions, I (and others) have noticed that the winds are more onshore (Easterly) out beyond the sandbar..and become more side-shore (NE’rly) as we head in towards the beach. This makes it easier to get upwind on the outside, but harder to get upwind closer towards the beach. The tidal acceleration has a good bit to do with this as well, especially on an outgoing tide. However, there is absolutely a distinct shift..or “backing” of winds to the side-shore directions- and this could easily be due to the surface roughness guiding the surface winds in its direction. It’s almost as if the deeper waters are host to a less frictional ENE/EAST wind than the shallower waters, which tend to gain surface friction from increased shallow water chop.
Here is a good example of what we might experience on any given NE–>ENE event. Isle of Palms is the island at the top, Breach Inlet then Sullivan’s Island to the left. Then yellow arrows represent the directions winds come from.
One important note: Once the sand bar becomes completely covered up by high tide, the wind direction pretty much becomes fairly uniform while the gradient weakens, resulting in the “drying up” of these wind rivers.
As we head into the Charleston Harbor, things get a bit more complex as land shadowing, river convergence and surface friction cause eddying and instability in the wind field. This divides the harbor into two sections – one for the main wind river pushing through in off the ocean…and a secondary wind river from the winds funneling down the Intracoastal Waterway. Here is a map of what is occurring on an outgoing tide. The wind rivers widen just a bit on an incoming tide as surface friction calms down.
So all-in-all, this article presents some newer material for the meteorological world as we continue to learn about our fragile coast. These Backdoor Sea Breezes are necessary to understand for many reasons…and extremely important to mariners, watersportsmen and the maritime community as a whole. As our coastal sensors, newer technologies and time on the water allow us to “see” more of what is going on, we may find even more of these nuances we never thought were there.
Or if you are in a rush take a look at the heat map above. Notice that much of the bulk of the earth ocean mass north of Antartica is out of whack temperature wise. All the orange and yellow in the oceans represents water that is warmer than the seasonal norms.
Ignoring the huge streak of El Nino hot water west of South America notice the mass of unusually warm water that extends from Baja past the Pacific Northwest into the Gulf of Alaska and well out into the Pacific.
That “Pacific Heat Blob” formed about 2 years ago and has been impacting our weather as well as encouraging the very unusual number of pacific hurricanes and the speed of their formation and their duration.
This week with Hurricane Patricia we saw fastest growing and strongest hurricane in history. While tropical storm Olaf east of Hawaii has been loafing around for weeks.
Hurricanes pump vast amounts of air into the atmosphere and in the pacific much of that air descends into the surface North Pacific High. So the North Pacific High, which is usually small and far away from the California coast this time of year , is still hanging around.
Changes always happen very fast out in the Pacific in late fall as storm system come crashing towards the west coast. What is different this year is the North Pacific High is large and robust so we will see some atypical NW clearing winds.
Check out the upper animation that shows the pacific today Tuesday Oct. 28. Check out the strong southerly coast storm winds from far Northern California all the towards Alaska. Also notice the tiny old NPH that will give us some intermittent weak NW wind today and the bulking up new NPH near Hawaii.
Then notice how dramatically different the pacific looks by Thursday. Especially focus on the side of the North Pacific High and the NW winds along the California coast.
Getting those winds into the Bay and the Southern California beaches will be tricky since the pressure gradient to the interior will be pretty weak but I would keep your eye on the coast and Crissy, Coyote & 3rd. this Thursday.
Plus just aloft the winds will be clocking from NW to NNW to N. and the later 2 directions tend to weaken and delay the arrival of the surface NW wind. The also make it very difficult to get winds deep into the Bay so even Treasure Island is iffy.
My forecast shift at Weatherflow ended on a Tuesday. Just 72 hours ago I made sure to check the Mexican Tropics to see if there was any possibility of a storm that might develop that could bring sub tropical moisture up into Southern California. There was a small disturbance that the National Hurricane Center (NHC) gave a good chance of development. I checked the models and there was nothing significant expected and nothing that would affect my forecast area and so I finished my shift and didn’t think anything more about the Mexican Tropics. Guess how shocked I was to come back to work and see one of the most powerful Hurricanes had developed from that small disturbance in just 48 hours. As I write Hurricane Patricia is making landfall near Puerta Vallarta, Mexico as a Category 5 storm with wind speeds at an incredible 190 miles an hour. Winds had been estimated by Air Force reconnaissance aircraft to be 200 mph at the peak of the storm with a central pressure of 880 mb.
The following animation shows just how fast this storm blew up. As you can see it wasn’t until 10 am on Wednesday that winds reach above the 39 mph for the storm to be categorized as a Tropical Storm. 24 hours later at 1 pm Thursday the storm barely qualifies as a hurricane. Then in the next 24 hours it explodes into a compact powerful category 5 hurricane that is now moving on shore.
For a hurricane to strengthen it needs a few factors including High pressure aloft and light upper level winds, which Patricia has, but many other tropical storms have these and don’t reach this strength. There will be a lot of analysis once this storm dies as to why it has been able to reach such epic strength. The smoking gun is likely to be the essential ingredient that a hurricane needs to develop and that is warm ocean temperatures and boy do we have that.
Oct 21, 2015 Global Sea Surface Temperature Anomalies
This graphic above shows sea surface temperature “anomalies”. That is the difference from the climatological average. Do you see just how much warmer than normal the ocean is along the Equatorial Pacific? That is the signature of the strong El Nino that is developing.
We are hearing lots about the El Nino here is Southern California as the expectation is that this warm pocket will strengthen the sub tropical jet and send moisture laden storms toward the area this winter. This summer we have seen an above average number of tropical storms and hurricanes in the Eastern Pacific. Hurricanes are named starting with the letter “A”. Patricia starts with a “P” meaning that there have now been 16 tropical storms in the Eastern Pacific while the Atlantic, which is usually the more active area, only has a total of 10.
But the Equatorial Pacific is not the only place that is warm. Take a look again at the map. Do you notice the warm water along the west coast of North America and in many other areas including the a large area in the Northern Pacific?
This year’s El Nino has been compared to the huge El Nino in 1997. The National Climate Center is forecasting a wetter than normal winter for Southern California due to the similarities in the strength of this year’s El Nino to the one in 1997 when Southern California was soaked by winter storms that brought in sub tropical moisture. But maybe that is not the whole story. Yes the Equatorial Pacific’s Sea Surface Temperatures look very similar. Here is how the Sea Surface Temperature Anomalies looked in October of 1997.
Oct 21, 1997 Global Sea Surface Temperatures Anomalies
Do you see the differences? In 1997 the Northern Pacific was cooler than normal as were the waters just off the East Coast line. Now in 2015 much of the world’s ocean are warmer than normal. It will be interesting to see how these other pockets of heat interact and affect the development of the sub tropical jet stream this winter. I don’t think we can simply count on the 2015/16 winter to be a cookie cutter of 1997 just because we again have a strong El Nino.
Analysis of WSW’rly Low Level Jet along the Long Island Sound the morning of 10/20/15
Forecast for the day called for moderate to strong SW/WSW’rly flow early on for much of the New England region, but with back door frontal boundary infringing on the region in the afternoon, potentially increasing clouds and chances for precipitation, the flow was expected to soften into the evening. See PM forecast below (excuse time stamp pulled from forecast UI post event):
Looking pretty good with no real surprises expected as I plow through the East Coast forecasts Monday afternoon. I lay my head to rest with little concern for forecasts that evening. While I slumber the never sleeping NWS WFO BOX notes some developing trends concerning mixing of the mid/upper level flow to surface along the S facing shores of LI Sound RI and Cape Cod. See 345AM forecaster discussion below:
TODAY… SOUTHWEST 35-40 KNOTJET ALOFT OVER THE SOUTH COAST AND OFFSHORE WATERS. OBSERVED WINDS AT 1000-3000 FEET ATJFK AND LGA ARE AROUND 30 KNOTS…BUT WINDS AT BUZZARDS BAY TOWER SHOW 37 KNOTS.BUOY 017 SOUTH OF MONTAUK PTREPORTED GUSTS TO 33 KNOTS PRIOR TO 2AM. DAYTIME HEATING WILL MORE EFFECTIVELY MIX THE WINDS TO THE SURFACE ALONG THE SOUTH COAST AND ISLANDS. POTENTIAL REMAINS FOR 35-40 KNOT GUSTS TODAY WITH THE BEST CHANCE ACROSS THE ISLANDS AND PARTS OF CAPE COD. MOST WIND SHOULD FALL JUST SHY OF WIND ADVISORY THRESHOLD…BUT CLOSE ENOUGH TO MAINTAIN THE EXISTING WIND ADVISORY FOR THE CAPE AND ISLANDS. INLAND…A GUSTY DAY WITH MIXING POTENTIAL MORE LIKE 20-25 KNOTS.
So by the time I wake at 545 Tuesday for the 7AM updates I see we have more than your run of the mill elevated zonal flow going on. See Observations below:
Not to worry its early and I will get these tables up to par before any of these Yankees even notice (excuse time stamp pulled from forecast UI post event):
So not really my proudest forecast, as I was low at many locales by 10kts+ but I was able to scramble and get in line for the AM update. Now lets look at what the set up was here so we can learn from my shortcomings.
Synoptic setup reveals strong but flat ridge of High pressure over the Mid Atlantic with deep layer troughing well to the N in Canada, which is rotating a frontal boundary towards the New England region.
I would argue that the surface analysis is nothing special and it certainly didnt jump out at me and say “hey man its gonna crank up there tomorrow”
Then we see the 700MB and 850MB upper air charts where we notice solid 30-50kt winds not far above the surface. Raob from Chatham below:
This strong wind aloft in combination with dry air (noted on our skew-T above) and the topography of LI Sound favorably oriented with 850MB wind directions allowed solid mixing and Venturi effect to occur. The end result was 30kt winds from Stonington to Chatham.
As the sun rose the flow generally faded, holding on only for a few locales while most spots had the averages fall closer in line with my PM tables, with plenty of stronger gusts. So lets keep and eye on this region as the cold season continues to develop.
Typically I look for this type of flow to occur in a postfrontal regime, and most often in a much less expansive scenario (i.e. Stonington to Pt Judith). But the extensive region of elevated WSW’rly flow surpassed any expectations for the day and any in my prior experience, even in a warm air advection scenario. So lets keep and eye on this region as the cold season continues to develop.
What is El Niño and how will it affect our East Coast wind pattern?
El Niño is basically the warming of the equatorial Pacific. Specifically for the effects it causes us in the United States, it’s the warming of water surface temps above normal along the eastern Equatorial Pacific. The higher sea surface temperatures indicate a warmer climate for the SW United States as this warmer surface air surges northwards away from the equator. Historically, this also causes the eastern half of the Unites States to show wetter and cooler winters overall. This particularly strong El Niño phase is expected to peak late fall 2015/early winter 2016 as Sea Surface temps climb nearly 3.6 degrees above normal. Then it could start phasing downwards into the Spring 2016.
All of this warm air bulging into the SW and NW United States creates the setup for the polar jet stream to repeatedly dip down into the Midwest to East Coast. Add a warm blob of warmer waters just south of Alaska…called “The Blob” in the meteorology world…and the pattern intensifies the downward slope into the eastern half of the Unites States. We can also say that strong western Pacific Cyclones/Typhoons getting swept up into the North Pacific Jet (that eventually joins the North American polar jet) shows additional surges of energy for these dips in the polar jet to increase in strength over the US. We call this “teleconnection” when we see these types of connections span across the globe – just as some of our powerful Nor’easters rip across the northern Atlantic and end up bombing out over Europe to bring high winds and huge swells there.
Here is the chart used for detecting changes in zones. Nino 3.4 and Nino 3 are the ones closer to the United States. The Nino 3.4 is the one more emphasis is given to:
According to the latest ENSO (El Niño Southern Oscillation) diagnostic discussion from NOAA, this event could peak +2° during a 3 month period in the eastern Pacific as of their mid-September findings – specifically in the Index Nino 3.4 region…and is already showing and upwards trend towards 2° . Notice the other two data sets provided from the 2 past events from 1982 and 1997.
Here are the detailed prediction models (temps above normal up the left side and along the bottom months are done in sets of three: JJA= June/July/August, SON = Sept/October/November, etc…) – highest being “NDJ” (Nov/Dec/Jan).
The pattern to expect from past research on El Niño events is a colder and wetter winter for the Deep South and mainly wetter for the East Coast. Here are the latest NOAA outlooks as of October 15, 2015.
This goes in accordance with several dips in the jet stream, known as “Rossby waves”…which bring multiple cold fronts/ upper Lows from west to east, followed by cooler air masses down into the South and towards the East Coast/SE Region. When we have this negatively tilted (downward bulging) polar jet stream, we have warmer S/SW winds, or low level jets, pull up from the Gulf of Mexico ahead of cold fronts. With Sea Surface temps being so much cooler than the air during the winter, we encounter what is called “marine layering”, which causes “decoupling” issues at the surface with winds. In other words…warm air cannot mix over the cooler, stable waters. This in turn keeps the S/SW’rly wind events on the lower end. When lower resolution models predict moderate to strong winds…we usually end up seeing much lower-than-expected winds from those directions. With that said, Louisiana tends to show the higher amounts of rain, which tells us that these dips occur more frequently down into the Midwest to create heavier rain (and snow/ice) events down along the central Gulf States.
Conversely, when the cooler air masses move in behind these fronts, we see strong Northerly winds carve down the coast. This is known as the “cold air advection process”, where colder air sinks down over the warmer waters and accelerates parallel to or in between the warmer coastal land masses.
So all-in-all what do we expect from El Niño along the East Coast as we head onto the 2015-2016 winter?
Two types of setups:
With the sharp dipping of the jet stream straight down the Appalachians into the SE and swooping up the coast, we see stronger Westerly winds below deep seeding upper Low pressures that develop down into northern FL, GA, SC that swing WSW up into NC. We can expect much stronger N/NNE/NE’rlies behind them. For the smoother dips with weaker cold fronts, we see weaker S/SW’rlies with room for some potential here and there depending on air temps ahead of them…and moderate to somewhat strong Northerlies wedging in behind. I don’t see many East winds from Atlantic High’s sticking at all due to the quicker movement of systems along this jet stream setup.
2. With a sharp dipping of the jet stream into the Midwest and Deep South(cold and wintry weather for them), cold fronts weaken as they approach and fizzle out in the Southeast due to marine layer decoupling, but get some boost to the north of OBX on the upswing. Basically, the S/SW winds are weaker in the southeast and stronger as they head up north where low level jetting can force a stronger flow. But even there, we see marine layering having its issues as well. Low pressures tend to develop offshore and slide up the coast, which creates longer lasting rainy periods with variable wind fields and weaker gradients along northern FL/GA/SC and SENC. High pressures following them show West to NW winds briefly pulse to moderate levels in the SE Region before being lifted. Usually a day or two at the most.
Overall…the #2 setup creates an overall weaker wind setup for South East Coast. However, as we head further north, we tend to see weak SE coastal Low pressures pick up momentum while swinging northeast across OBX and heading towards Cape Cod/Maine – or further offshore. Winter events are triggered along these Nor’easters as wrap-around winds get the cooler bite from Canada – and there are many stronger, yet messy, NW/N’rly wind events as a result of the tightening gradients between Atlantic Lows and the Canadian Highs.
Ok so which one would I go with for this El Niño event?
Based on the latest NOAA discussion, I pick door #2 for a weaker overall wind pattern. Specifically, weaker overall Southerlies, average NE/ENE’rlies and weaker Westerlies. However, nothing is certain with a weaker wind pattern for us along the East Coast, though. We will be watching this closely to see just how similar it performs as compared to the past events. For research purposes and detailed analysis…we should be keeping track of mainly 3 sets of winds – I placed a blog link with each one for more details:
– S/SW winds ahead of fronts – how much do they build or how do they not build? Marine layer decoupling issues? At what temperature spread does marine layering/fog banking occur? What is the UP and DOWN pulse rate as a result? How are the lee-side land masses allowing builds inside of the coastal breaks, sounds and bays? http://blog.weatherflow.com/marine-layering-effects-start-in-the-se-region/
– NW/N/NE winds – how fast do they build into a region or specific areas? How long and how strong do these last for? Are they a tighter and higher quality gradient wind? Cold air advection process – what is the criteria for the much cooler denser sinking air? Does it accelerate along the various land and sea interfaces? Backdoor Sea Breezing with cooler air/warmer land? http://blog.weatherflow.com/early-fall-noreasters-for-2014-record-low-temps-on-the-way/
So…we have a big assignment to look forward as we swing from 2015 to 2016 during a very strong El Niño event. Let’s see how things play out. One great thing to keep in mind is that we have more WeatherFlow coastal sensors now than ever to help record this climatic event.
In this first animation we are seeing the Cut-Off Low at ≈ 18,000 ft. that is currently west of Southern California. Cut-Off Lows are called such since they pinch off from the largely WEST to EAST winds the circle the earth far above the surface. When this happens the counter-clockwise spinning winds that make up the Cut-Off Low are more or less free to wobble about in a hard to predict fashion.
The position of the current Cut-Off Low has its counter-clockwise spinning winds bringing clouds and a chance of showers to Southern California. Meanwhile below the Cut-Off Low there is a huge dead surface wind zone right where the surface North Pacific High would normally be located in the fall. This set up has caused very light winds for the Bay Area in recent days as you saw in yesterdays blog.
Today the Cut-Off Low you see in this image begins to move to the east. As this happens the North Pacific High begins to reform at the surface and over the next 4 days the North Pacific High’s surface NW winds begin to build along the California coast and the Southern California bight.
So what happens to a Cut-Off Low when it departs of west coast waters. Or more precisely what happens to make it depart?
The next animation shows the fate of this Cut-Off Low. First note the day and time data at the bottom of the animation. Looking at the numbered captions notice the Cut-Off Low at 1. and the winds circling the Cut-Off Low.
Now look to the west at #2. You are seeing a southward extending loop of upper level winds or upper trough moving in from the west. Watch as this upper trough slides towards California bring southerly wind at ≈ 18,000 ft. over California.
Watching carefully you can see that this upper trough sucks up the Cut-Off Low and by late Saturday the Cut-Off Low has disappeared.
Now watch as the upper trough itself slides off the screen to the NE. At the same time a northward extending loop in the upper level winds moves in from the west. Note how this brings very strong NW winds over Northern California and WNW winds over Southern California.
Some of the energy from these upper level winds will add a gust factor to the North Pacific High’s surface NW winds which are also ramping up this weekend.