Ocean Science 101: Upwelling, Downwelling, and other random acts of shrinkage

I’ve been getting a lot of questions this summer about upwelling and downwelling and while I have written a lot about the effects of these phenomenon I haven’t really took the time to sit down and explain exactly what they are…so here it goes, I will try not to get two nerdy in the explanation but hey no promises.

Upwelling



Most of you know or have heard the term upwelling and that it usually means that it is time to break out a thicker wetsuit, put away the boardshorts, and in some areas get ready for the combination ice-cream headache duckdive and the “claw” that your hands twist into after an extended cold water surf session. Just in case you haven’t heard of upwelling I will give you the quick and dirty definition first, which is: Upwelling is a process where cold water at the bottom of ocean is pulled from the lower depths and is brought to the ocean surface.

If you really want to get into the oceanography-nerdery there are actually 5 types of upwelling being researched by oceanographers:

1. Coastal upwelling
2. Large-scale wind-driven upwelling in the ocean interior
3. Upwelling associated with eddies
4. Topographically-associated upwelling
5. Broad-diffusive upwelling in the ocean interior.

The main types of upwelling that affect us as surfers are coastal upwelling and upwelling that are associated with eddies (which for Southern California are essentially the same thing.) more...

Visit the Solspot.com website to get the full scoop

Ocean Science 101: SoCal’s North Pacific Swell Window

Since we have started moving into the fall/winter season I have had a few people ask me about the W-NW swell directions...in particular they were curious about the swell shadowing that occurs in Southern California as swells start to track in from over the 300-degree mark.

A couple of notes on swell directions

Just for a quick refresher...when I am talking about swell-direction in "degrees" I am referring to the degree range on a navigational compass. (So North is either 360- or 0-degrees, East is 90-degrees, South is 180-degrees, and West is 270-degrees). You measure swell direction from the direction a swell is approaching a fixed point (we measure wind the same way). So if swell is coming from a storm to the NW of your position then the swell is a "NW swell" even though it is heading SE. It sounds confusing at first but once you think about it for a second it makes more sense. Here I drew a picture...



On the more technical level I use True-North directions as opposed to Magnetic-North (what an actual magnetic compass would register). Most maps and swell models are based on True-North since it is a more consistent value and not subject to the Earth's slowly shifting magnetic fields. Since I like to have consistency in my data, and I am just too plain lazy to constantly do the math, I use the True-North.

Sometimes, thanks to the difference between the 2 Norths, you get some confusion on what sort of swell direction a beach is exposed to. This confusion is usually compounded by some of the buoys and swell models that "average" swell-directions giving you a skewed degree reading thanks to the wider mix of swells, rather than the pure swell direction that is creating the surf. This can make it seem like a swell is coming in from a steeper swell angle when it isn't even geographically possible. This isn't a huge issue normally but I get bummed out when you guys miss surf or burn gas checking spots that won't be breaking...so I try and make sure that we are all on the same page with swell directions.

Ok back to the North Pacific swell shadow...

There are actually two components that block NW swell...

1. is Point Conception, the massive headland that forms the Northwest corner of the Southern California Bight.

2. is the Nearshore Islands, which include the Channel Islands, Catalina Islands, San Clemente Island, Santa Barbara Island, and San Nicolas Island.



Generally Point Conception blocks all of Santa Barbara, Ventura, and North LA while the Nearshore islands soak up the rest of the swell heading toward the South Bay, Orange County, and San Diego.

NW swell (295-310+)

I went back and picked out a few historical images from the CDIP to give you a visual on the swell shadowing. This first image is a NW swell (295-310+) with most of the energy coming in from above the 300-degree mark.



At first glance you can see how much energy is being shut out of SoCal, it has nearly 10'+ of swell (bright green color) showing through the outer waters and less than 4' showing at most of the areas along the SoCal coast (blue and dark blue colors).

When you start to focus in on the details a little bit you can see some minor windows where swell is leaking through the shadowing.

Ventura and the South Bay are both seeing some energy slipping through the gap between Point Conception and the Channel Islands.

Further south you can see a bigger chunk of swell making it through the area between the Channel Islands, San Clemente Island, and Catalina that is heading toward San Diego, particularly Southern San Diego.

One thing to remember with NW swells is that swell-period is really important...the swell in this picture is a longer-period swell, probably close to 16-17 seconds...and as the swell periods get longer you see more refraction, or wrap, off of the sea-mounts and shelves that hang out in the nearshore waters off our coast. Basically the edges of the swell shadow get "fuzzy"...there isn't as clear a delineation between the areas that will pull the swell. The swell hitting Ventura in this image is a great example, as well as the areas of North San Diego.



You can see a slight upward curve to the swell as it wraps around the nearshore islands for both of those areas. If the swell period was short, say around 8-10 seconds (or lower), there would be no curve to the swell...and the edges of the swell shadow/window would be very sharp...sometimes to the point where you can have surf hitting one spot 100-yards away and nothing at the spot you are sitting at.


WNW swell (285-300+)

Here is an example of a WNW swell...and while most of the raw energy is above 300+ degrees it is showing plenty of energy in the 285-300 direction range.



First off ignore the sudden change in the color for the different swell heights, I am not sure while the CDIP changes the colors as more swell hits but it is aggravating...if you don't check the scale you can look at the map and think that you are seeing a waist high swell when in fact it is like 10-foot...anyway.

As you can see on the map as the swell direction starts to shift more westerly you get a lot more energy making it into Southern California.

The WNW swell direction still has some shadowing issues but not as much as we would see on the NW swell. The spots that did well on the NW swell do even better on the WNW'er...so Ventura, The South Bay and South San Diego will be the biggest but you start to see some decent energy moving into parts of Southern Santa Barbara/North Ventura, areas of Orange County, and North San Diego as well. There are still a few blue gaps but they are much, much smaller.


W swell (260-280)

Finally here is an example of a pure W swell...this one doesn't have any northerly components of swell, just pure W energy. (Again the colors change so make sure to read the legend).



West swells are one of the "magic" swell directions...it is one of the few swell angles that can pass energy almost directly into SoCal without interference...which is one of the reasons why the swell heights on this model are so big.

You can see that the winter top spot like Ventura, the South Bay, and San Diego do even better on the W swell, pulling in more energy than the other regions. At the same time there is plenty of swell making it into almost every other region with a couple of shadowing exceptions behind the bigger nearshore islands like Catalina and San Clemente island.

It is worth noting that on swells this big sometimes it is better to look at where a swell is "not" hitting. This swell in particular was producing double-overhead+ surf at the standouts which puts the wave heights out of most people's comfort (and safety zones). Big W swells (if the weather is good) are good swells to hunt around for better shaped surf if you don't mind sacrificing some size and consistency.


To finish up...

The NW swell shadow is a pretty straightforward feature in hunting for surf in SoCal...but you still need to be aware that it is there. A good rule of thumb is that as swells approach the 295-300+ degree range your surf spot options get more and more limited. Once the swell goes above 300-degrees most spots will shut down completely unless the swell period is super long so don't spend a lot of time driving around as the swell gets steeper. Oh and make sure to do a few special wave dances so that we get mother nature to kick out plenty of W swell this winter!

Ocean Science 101: How to use the NOAA and Scripps Buoys

I am sure that this will be a review for many of you out there but I thought I would through together a little instructional post on how to use the various types of buoys that we have in the Southern California area.




On the surface buoys are pretty simple to understand. They are basically floating sensor platforms…part weather station and part ocean measuring system. They give us near real-time observations of ocean and weather conditions, usually for a fixed point near a coastline or sometimes in the deep ocean water.

Weather buoys have been around for a long time…they used to be the lifeblood for oceanographers and meteorologists before we had reliable weather satellites. They started out fairly simple measuring wave heights, ocean/air temps, and wind speeds if you were lucky. They were effective though…and for many years they gave the coastal areas, sailors, and surfers advanced warning of incoming storms and increasing seas.

Today buoys are pretty sophisticated, they can give you precise information on incoming swells, even with multiple swells running at the same time. They gather data on wave heights, swell-periods, swell directions, water temps, wind-speeds, wind-directions, and barometric pressure, all of which is broadcast in both radio and digital formats. The digital information is processed by NOAA (and Scripps Institute) computers and is eventually updated on the internet.

With all of the new satellite information and computer wave-models nowadays I think that buoys sometimes get overlooked…or at least people don’t use them as much as they should. Satellite information is great but it is generally pretty small-scale…or so narrow in its view that it misses out on key information. Wave models are good but they are the end result of crunching the mass of data spit out by the various pressure models…and if they get crap data going in (like underestimating the strength of a particular area of fetch) then you get crap data coming out (a wave forecast that misses a swell entirely). With buoys, if they are functioning properly, you get actual measured empirical data. If the buoy is close, or at least geographically relevant, then the buoys are a great way to validate a forecast, or make adjustments as necessary.

For the average surfer the buoys are a great way to paint yourself an accurate picture of what is happening swell-wise and wind-wise in our local waters. Armed with that knowledge you can make good choices on where and when to surf, keeping yourself safe and, almost equally important, helping you score some quality waves.

The two types of buoys

For Southern California there are really just two main types of buoys…and it isn’t that the buoy systems use radically different equipment…it is more about which organization runs/maintains the buoys and how each group presents its information for public consumption.

The two types of buoys are:

1. NOAA Buoys
2. Scripps/Coastal Data Information Program (or CDIP)

Personally I like the Scripps/CDIP buoys better…particularly for Southern California. NOAA’s buoys are good, they have the outer deepwater buoys which are awesome for advance warning of NW swells, but they present their information in a much more convoluted manner that screams government bureaucracy and information systems built by low-bid contractors. What is funny is that the NOAA buoys can actually do almost everything that the Scripps buoys can but you need to repurpose the data in a more useful format.


Finding, understanding, and using the Buoy Information for Southern California

Ok now that we got the background information out of the way I am going to walk you through how I personally use the buoy network, which encompasses NOAA and Scripps/CDIP equipment.

We sort of have to start with how to find and use the buoy info.

First off…probably the most useful and 100% free buoy website is http://www.lajollasurf.org/. This site has been a fixture in my forecasting repertoire pretty much forever…long before I ever became a professional surf forecaster…hell it has been a favorite bookmark since I have had the internet.

So using lajollasurf.org you have a couple of choices in how you start to look at the buoy data…it all depends on preference.

If you are a visual person then I recommend starting here…http://www.lajollasurf.org/buoys.html




If it just looks like your computer threw up all over the page don’t worry…that is normal. If you couldn’t tell it is a bit jumbled at first but you can click on the socal region and eventually it ends up narrowing down the focus to this…

(link to live data http://www.lajollasurf.org/socal.html )



This is more detailed with a larger scale…it helps you get familiar with the locations of the buoys, which can help you determine if the buoy is being shadowed by the coast, nearshore island, or other features. I recommend this view for people that are just getting into checking the buoys…the map view helps you piece the whole picture together much faster.

From this page you can see the current buoy conditions, including the dominant swell direction and swell period. It also overlays it on top of NOAA’s WaveWatchIII swell-model, which is the psychedelic color scheme in the background.

You can mouse over each of the buoys (NOAA buoys with the red arrows and Scripps/CDIP buoys with the blue ones)…



and click one of the buoy stations to get more specific data from that buoy.


NOAA Buoys

You read above that I am not all that stoked on the NOAA buoys…this next section is exactly why.

When you click on a NOAA buoy it lobs you into NOAA’s buoy pages…here check out this live link…http://seaboard.ndbc.noaa.gov/station_page.php?station=46047&unit=E&tz=PST




As you can see it gives you a ton of information…which is ok if you are looking for current info, which is summarized on the first page. But if you need historical data, (which we do because swells do hit in the middle of the night), it disjoints it…so you have to visit different sub-links to paint yourself an accurate picture of what has been going on since you last looked at the buoy.

If you need to get older data then, for most people, I would recommend just clicking the chart-info button for the most important data points…wave-height, swell-period, wind-direction, and mean-wave-direction.



This is the data that you would see…




I know what are saying…

”seriously Adam I have been reading about all the cool shit a buoy can do and you show me this piece of crap”

Trust me I feel your pain…leave it to the government to suck the fun out of something.

Actually this brutally ugly chart is telling me some pretty important info…check this out.




See how the dominant swell period has been holding around 10-12 seconds for the last few days…then it suddenly jumps up to the 22-second swell periods? This is a good indication of some sort of change. Either a new swell is arriving or the other shorter period swell is dropping to a point where the long-period swell becomes dominant. By itself it doesn’t give me the full picture but if I bring in the other buoy info, and my forecast, I can validate that the new SW swell has started to arrive…and that I should start working on my hacking cough so that I can sound convincing when I call in sick to work tomorrow.

It is a lot of work to get info out of the NOAA data…personally I use them for mostly current data…unless the buoy is one of the far-offshore ones that has no Scripps/CDIP counterpart.


Scripps/CDIP Buoys

The data format from these buoys blows doors off the NOAA stuff…about the only drawbacks to these buoys is that they don’t easily present historical data that is older than 24 hours and that they don’t display wind speed/direction.

Here check out a live link…

http://www.lajollasurf.org/oceanside.html




Ok on this buoy page we have all of the summarized and historical data accessiable on the same page and in the same format. It also gives us the full spectrum of swell-directions and swell-periods of the energy in the water at the recorded time.

If you look at the cool looking roulette wheel-thingee at the top left of the graphic. This is showing the current swell-directions, broken out by swell-periods.

The percentage table on the top right shows the distribution of swell energy, by swell period. The graph on the bottom left shows the same thing but in a visual format.

If you mouse-over either the bar-graph or the swell-direction compass you will get that actual “wave-height” of that spectrum of swell-period. So, on the pictured chart for example, you can see that there is 1-foot of swell with 18-second swell-periods coming in from a 200-degree swell-angle.

The grey trending chart shows the historical “combined wave height”…but if you mouse over the chart…say at the -12 hour mark…the rest of the graphic will change to reflect the data that was captured 12 hours earlier. This is a great way to see when a swell started to arrive, how long the initial swell periods where, and how strong it was when it started to show…all of which are good indicators of how strong a swell, and how good of a wave maker, it has the potential to be.

NOTE: There are couple of weak-points to this display…one is that if you have two swells coming in from different directions but with the same swell periods the display will average the swell direction between the two actual directions. So instead of having two swells, one from 260-degrees and the other from 200-degrees, you get one swell coming in from 230-degrees. The other weak point is that the swell is broken up into neat little sections that don’t always reflect the true nature of the swell…particularly if you have more than one swell in the water. Many times you will miss the lower-periods of the swell because they are being “averaged” in with another swell from a different direction. Again this is a good reason to use the buoys in conjunction with a forecast.

Sorry went off on a little tangent there…ok Back to using the buoys

OK here are the steps that I follow.

1. Read the forecast – at bare minimum it gives me a baseline to start working from…even if it is totally wrong (you probably got it from wetsand or something). You will know that you should be looking for something.

2. Check out the buoy map – (or if you are more experienced use the buoy summary list… http://www.lajollasurf.org/buoylist.html)

3. Drill into an applicable buoy – pick a buoy that is close to your location.

I would recommend the Harvest Buoy as a good starting point…it is the most exposed. It sits right off the tip of Point Conception and has no blockage from either the S or the NW…basically you get a clear “pure” view of the swell along the California coast.

From there I would pick a buoy close to your area.

For Santa Barbara and Ventura I would recommend the Goleta Point and Anacapa Pass buoys.

Los Angeles should focus on Santa Monica and San Pedro (which is a little more exposed to W swells).

Orange County has the Dana Point, San Pedro, and Oceanside buoys.

San Diego is lousy with buoys (I guess it helps to have Scripps right in your backyard). I would use Oceanside buoy for S swells and a mix of any of the others, like Torry Pines for WNW swells.

4. Finally just cross check the forecast for confirmation. Is that S swell showing on the right buoys? Is it making it into my beach? Does it look like Trestles or Newport will be the call this morning?

5. If things look correct (or better) then go surf…get off the computer…seriously don’t waste another minute…well unless you are going to click a few more google ads for me…uh then go ahead and spend a few more minutes.


Well that is about it…

I know that was a lot of information to process…it isn’t as complicated as it appears at first…just keep practicing and it will start to click for you. As always if you have questions let me know…I am happy to help you out, hopefully without further brain hemorrhaging.

Ocean Science 101: How our surf is made (Part 4: Breaking Waves)

Breaking Waves

This is where all the hard work of tracking a storm, watching a swell form, and then tracking it halfway across the world pays off. Breaking waves are the end result of all of this storm and swell activity...they are the meat and potatoes of surfing. In fact most surfers, in particular experienced surfers, know a lot about breaking waves, and know it on an almost instinctual level.

The size, shape, and power of a wave determine what and how we ride. You see it everywhere, from longboarding slow soft waves at Tourmaline or San-O, or driving down fast hollow sections at 56th Street on your fish, or big arcing cutbacks on your thruster as you speed through long sections at C-street. The characteristics of the breaking wave will set the rules on what type of board, gear, or surfing style is going to work the best.

Shoaling (waves hitting the beach)

Shoaling is the actual process of a swell moving from deeper water, turning into a wave, and eventually breaking along a surf spot.

Part of this process is actually driven by some of those characteristics of swell period. You may recall back is part #3 where I said that the energy in a swell actually extends downward in sort of a swell “column”…well shoaling starts to occur as the swell energy starts to reach the sea floor.
As the water depth decreases the energy of the swell is forced upward, which make the swell on the surface start to increase in height. As the energy moves into shallower water the swell starts to take the shape of a wave. It is important to note that the energy that is being squished into the sea floor is starting to reduce in speed thanks to friction. Eventually the water depth reaches a critical point where the wave can no longer support the top portion of water, which is moving faster than the base of the wave, and everything destabilizes. This is the point were the wave breaks and the crest of the wave spills forward in front of the base releasing a good portion of the waves energy.

Wave Shape

Wave shape is determined by a few different things. Water depth, swell-period, swell-height, and the shape & orientation of the beach can all play very important roles in wave shape.

Waves generally break in a water depth that is about half of the wave height. So an 8-foot wave would potentially break in about 4-feet of water. The actual math for determining water depth for a breaking wave is actually a lot more complex but the 1.75:1 or 2:1 ratio is a good general rule of thumb.

How the breaking portion of the wave is shaped is almost exclusively determined by water depth. Almost all waves that can throw decent barrels have the same characteristic…they all have a sea-floor that goes from very deep to very shallow in a short distance. In opposite of that is true as well…most longboard waves have a very long-gradual sea-floor shape where the wave slowly loses power before it finally spills over.

Now beyond water depth, the energy in a swell (both period and wave height) makes a difference in wave shape as well. The more energy in a swell the quicker it starts feeling the sea-floor and the more energy it has to spare creating the wave as the swell starts to shoal. A large long-period swell can throw some solid dumping waves on even the most gradual of sea-floor slopes. The converse is true as well a small short-period swell can make it almost all the way to dry sand before it has to break…and in some cases it may not break at all…just surge on to the beach in a sort of last gasp sputter.

Lastly beach shape and orientation are also important factors and can basically make or break a wave. In the case of both of these it is almost the imperfections that can cause a well shaped wave to form. Maybe it is a deep hole that has formed in the sandbar, or a jetty that piles up sand on one side but not the other, or a chunk of reef that is missing, or even a simple headland that has slowly eroded into place over the millennium…all of these “imperfections” in the sea floor allow a wave to break unevenly. The uneven breaking means that there is still an open rideable section ahead of the breaking section, and in cases where the sea floor is nice and steep the wave can be moving fast enough to create a hollow section. (if you are lucky, or if you live in Indo, which is sort of like being lucky all the time).

Constructive and Destructive interference (aka combo swells)

Some wave shape is determined by the types of swell directions that a beach is exposed to. When you have a beach with an open swell window you can get what is called constructive and deconstructive interference. This occurs when you have 2 swells coming in from different directions that hit the beach at the same time.

The overlapping nature of the swells, and the peak-to-trough-to-peak pattern, means that in some areas the swells will double up energy creating a taller breaking wave, and in other areas the swells will cancel each other out and there will be no waves at all.

This is the process that sets up those crossed-up, peaky days. These swells are actually more fun on a wider beach with a fairly consistent water depth…basically beaches that would normally close out on single swells like most beach breaks. Other breaks that have a more varied water depth can still be fun but generally don’t work as well as they could on a single pure swell.

Wave Refraction

Refraction occurs when a wave starts to feel the ocean floor. What happens is that the energy in the wave or swell starts to feel the sea-floor and begins to slow down thanks to friction. As the wave slows down it starts to change direction, generally pulling the waves energy toward shallower water.

Refraction can occur in all kinds of different water depths…long-period swells can feel the bottom at about 1000-feet, so you can start to see influences of refraction quite a ways offshore. Short-period swells don’t feel the bottom until much shallower water depths and can experience refraction in as little as 15-20’ of water.

Probably the most dramatic, and for surfers one of the most fun, examples of refraction is what occurs at point breaks.

At a point break you generally have a small headland that extends out into the deeper water along a coastline. Now most points are not sheer cliffs, they have a sea-floor that slopes away from the headland…usually this shallower area drops off pretty fast, particularly as you move along to the inside sections of the point…if you are very lucky there will be a deep bay protected by the point.

What happens is that the swell will hit along the top of the point and start to break as it hits the shallow water there. As the wave moves past the top of the point the energy that is still feeling the shallow water will continue to pull back towards the beach effectively extending the breaking portion of the wave…if the point is shaped properly, and the swell period is just right, it will wrap a ton of energy around the point and set up a very long ride. Next time you see Rincon on a big swell watch how the wave wraps in.

Wave Reflection

The last process that affects a breaking wave is called Reflection. This occurs when the swell energy hits a solid object, like a jetty or a cliff, and bounces off. Usually the wave will lose a lot of energy in the “bounce” but if the rest of the beach is shaped in the right way you can actually get the bounce energy to reflect back and add energy into a portion of the swell that did not hit the object.

Probably the best example of this is the Wedge in Newport Beach…hell the name alone should explain the process. Basically you get a big S swell that marches down the end of the North Newport Harbor Jetty. The swell instead of spreading out as it moves into the beach starts to pile up water and energy along the jetty. Eventually the swell moves out of the very deep water into extremely shallow water (or sometimes dry sand) and the energy piled up along the jetty bounces across the breaking wave, creating a large wedge shaped peak that throws some of the most retarded looking waves in SoCal. Other spots that are good, but lesser publicized, examples of reflection, are Surfside in HB and South Mission Jetty down in San Diego.


What this all means

I really believe that the more that you can learn about the ocean the better of a surfer and waterman that you become.

I don’t think you need to be an oceanographer, a meteorologist, or a surf-forecaster to have fun and score a few good waves (though it helps to be a surf forecaster)… but I think it is important to have at least a minimal understanding of the processes that go into creating surf.

Once you start to get some of the basic concepts down you will start to see how everything is connected, and eventually (at least in my experience) you will start to make better choices when it comes to surfing. You will find yourself getting more, quality surf, with smaller crowds, and better conditions…and really as a surfer can you ask for anything more.

Part 1: Overview – Types of Waves
Part 2: Wave Creation and Swell Generation
Part 3: Characteristics of swells

Ocean Science 101: How our surf is made (Part 3: Characteristics of swells)

Swell

The swell stage of a wind wave life-cycle occurs both in the generation phase and the swell phase (duh Adam), which is why the surf gets big when a storm or heavy winds move right over your beach. Usually though the swell phase occurs when the energy of a storm moves away from the area it was created.

As the swell energy moves away from the storm center it becomes more organized and structured. The energy generally moves along the path that was established by the strongest areas of fetch, but because storms are circular in nature swell move out in all directions and is very similar to dropping a rock into a pond…a better description though would be a rock thrown into a pond, where the biggest waves move out along the direction the rock was traveling when it hit the water (stupid rock analogy).

We measure swell energy in a rather unique way…it is actually a time based measurement called swell-period. This refers to the interval between the passage of two successive swell crests past a fixed location in the ocean and is measured in seconds. Swells with periods of 16-seconds or more are generally referred to as “long-period swells”. Swells in the 12- to 15-second range are considered “medium-period swells”. Swells that are 11-seconds and below are called “short-period swells”



Generally the longer the swell-period the more energy it has and the faster it moves. So as swell first starts to leave the storm area all of the swell energy will be piled up and moving more or less together but as it starts to travel across the longer distances the swell energy starts to separate. The long-period swells move faster than the shorter ones so eventually they out-distance them.

The longer the distance between the storm and the beach the more separated out the swell periods will get. For example a swell generated several thousand miles away in the South Pacific will arrive with very distinct differences in swell period. The swell will hit the buoys with the long-period energy first and will follow the progression down through the shorter periods.

A closer storm, like the ones that form just off the coast of California, will blast us with the full spectrum of swell periods almost at the same time…you may get a little jump in long-period energy first but then the peak of the energy will come through in a large lump…it may jump from a 18-second swell straight to a 12-second swell and peak with a bunch of energy in-between.

More Random and complicated stuff about swells

Swells are complex beasts and they live in a weird state of physics, which makes them even more complicated.

To even start the discussion you need to know (and hopefully understand) a thing known as the Coriolis Effect.

Wikipedia describes (because I am getting a headache) the Coriolis Effect as “an apparent deflection of moving objects from a straight path when they are viewed from a rotating frame of reference.

Freely moving objects on the surface of the Earth experience a Coriolis force, and appear to veer to the right in the northern hemisphere, and to the left in the southern. Movements of air in the atmosphere and water in the ocean are notable examples of this behavior: rather than flowing directly from areas of high pressure to low pressure, as they would on a non-rotating planet, winds and currents tend to flow to the right (left) of this direction north (south) of the equator. This effect is responsible for the rotation of large cyclones”



On the surface this seems straight forward enough but with swell it takes on a slightly different twist. Coriolis only affects objects with mass. A swell is almost entirely energy, which has no mass, so it is NOT affected by Coriolis. (I really hate physics sometimes).

The tricky part is that air and water molecules have mass, so you have to take Coriolis into account when you are dealing with currents and storms, (basically all the things that help to create a swell), but the second a swell leaves a storm area as energy in the water it is no longer affected by Coriolis.

I am sure a lot of you are swearing at me right now for even bringing this up but it actually plays a very important role in tracking swells. Because the swell is not affected by Coriolis it travels in a straight line. You can basically draw a line from the storm’s fetch straight to your surf break…if no land gets in the way then you will see waves from that swell.

Important Safety Tip: Oh yeah that straight line, from storm to break, has to be on a globe…not a flat map…when you draw it on a flat map you have to take into account the curvature of the earth, which means that the straight line has to curve along what is called a “great circle line” or is sometimes referred to as a “Rum Line” in ship navigation.

Swell decay

From time to time you will hear a term called swell-decay…this is another one of those tricky concepts. Remember a couple of paragraphs ago when I said swells are energy and have no mass? Well it is not entirely true…if a swell was pure energy it wouldn’t have any friction and all swell periods would move at the same speed and be able to travel across the entirety of the ocean. In reality there is a little bit of mass in a swell, or at least friction.

This occurs as the swell moves through the water…the energy actually extends downward as well as along the surface. The longer the swell period the deeper the energy goes. In this “column” of swell (for lack of a better word) there is some circular motion of water molecules. It is this slight motion of actual mass that allows some of the swell energy to bleed off as friction. In short period swells there is a lot of this circular motion (mostly because the swell’s waves are so close together). It is this energy reduction that is usually referred to as swell-decay.

What happens is that swells will lose energy as they travel longer distances…the longer they go the more they lose. Short-period swells lose the most energy the fastest…so a swell with a period under 10-seconds can only go a couple hundred miles before it has lost so much energy that it can’t create waves any longer.

A long-period swell decays much slower and will only lose a small amount of energy over long distances. It is possible for a 18-20 second swell to travel thousands of miles and only lose 2/3rds of its energy before it hits the beach. So if a swell started off with 10’ of long-period energy it would still have almost 3’ of energy when it arrived at the beach.

This is one of the reasons why Southern California never gets short-period energy from the South Pacific…all of it decays away before it reaches us.

Part 1: Overview – Types of Waves
Part 2: Wave Creation and Swell Generation
Part 4: Breaking waves

Ocean Science 101: How our surf is made (Part 2: Wave Creation and Swell Generation)

For surfing wind waves are the end-all be-all of the sport. Without wind waves there would be no surfing at all…so everything else like conditions, tides, beach shape, it is all just window dressing.

Generally wind waves have 3 different phases in their life-cycle; Generation, Swell, and breaking waves.

The first is generation, which occurs underneath a consistent area of winds going the same direction, called a Fetch.



Fetch can occur in a variety of situations and can be found in anything from a frontal storm, hurricane, trade winds, or even just consistent winds around an area of high-pressure. Fetch is measured in 5 ways.

1. Intensity – the strength of the winds in the fetch area

2. Length – how long is the fetch? This can affect the swell strength…think of the fetch-length as a rifle barrel…the longer a swell can stay in the “barrel” the more energy that the winds will be able to add to it.

3. Width – How wide is the fetch? The wider an area of fetch the broader the swell direction will be…this is particularly important for SoCal where a spot can get totally skunked by a swell that is just a few degrees outside of its swell window.

4. Duration – How long have the winds been blowing on a particular area of ocean? The more time they spend the bigger a swell can become.

5. Movement – Storms and Fetch are not stationary…they are in constant movement. Direction of movement is very important. The more that a swell moves “toward” a spot the more energy that it will impart to the swell. If the fetch is moving obliquely or away from a location that hampers the swell strength. Speed of movement is also a factor…if the fetch area moves to fast or to slow it allows the swell to move out of the area and away from its energy source.

Once an area of fetch has been established, (hopefully aimed at and moving toward your surf spot), and the winds are blowing over the surface of the water they start to impart energy into the ocean as the air molecules run up against the water molecules (I just really wanted to write molecules in this post somewhere). The friction between the air and the water is the process that moves energy from the atmosphere into the ocean.

At first, if the sea is calm, you will start to see small ripples forming as the friction from the air gains purchase. These are called capillary waves.


Capillary waves act like grip-tap on a skateboard…once they have formed they add a more exposed surface area to the wind allowing it to gain more purchase and add more energy to the waves (I bet you can see where this is going).

If the wind is strong enough these capillary waves continue to grow along with the space between the crests of the waves. Once the larger waves are formed this is sometimes called a sea-state (or at least sea-state refers to the conditions of the seas within the target area).


As the winds become more intense, or the duration of the wind becomes longer. These waves grow.



And grow…



Eventually if the winds are super intense you get huge waves at the storm core. (The boat in this picture is bummed).



Now an area of fetch doesn’t have to be world-ending intense to create a swell. You can have a swell with almost any amount of wind, but the more wind, the bigger the seas, and the larger the fetch. The larger the fetch means that more energy will make it into the swell, which in turn means that the swell will have a better chance of making it across a longer distance (eventually hitting your break).


Part 1: Overview – Types of Waves
Part 3: Characteristics of swells
Part 4: Breaking waves

Ocean Science 101: How our surf is made

OK this will probably review for a lot of you, but I thought I would go back and cover some of the basics in surf forecasting. I have been posting forecasts, reports, maps, and other random nonsense for a while now and I started to realize that a lot of the stuff that I have been throwing at you assumes that you have an idea of how our surf is generated. It isn’t really that hard to find on the interweb, (I mean, come on, that is what Wikipedia was invented for people), but I decided to throw it up here too so that you didn’t have to hunt around for it.

Why it matters

I am sure that there are some of you out there that don’t really care about where the waves come from and are fine with just knowing if the surf is going to be good tomorrow. That is totally cool…I hope that I keep my forecasts simple enough that you can keep scoring…or at least save some gas money now and then.

Personally I think that you become a better surfer, and a better waterman, if you get in tune with the ocean, the weather, and the processes that create the conditions that we, as surfers, are looking for. You don’t need to be a forecaster or anything but I do think that knowing the general principles behind how waves are made will keep you a step ahead of other surfers, which is nice, particularly when that step could mean the difference between scoring empty surf and slogging it out with the rest of the crowd that is a day late and a dollar short.

Types of Waves

There are actually 3 types of waves that occur in the ocean.

1. Tsunamis
2. Tidal Waves
3. Wind Waves


Tsunami



Tsunamis, if you were living under a rock or something, are waves that are usually generated by earthquakes. They actually used to be called “Tidal waves” because of the way they behaved as they hit an area. The true definition is that a Tsunami is actually caused by anything that quickly displaces a large amount of water. That could be anything from a volcanic eruption, a collapse of an undersea cliff or shelf, an asteroid/meteor hitting the ocean, or even something man made like a nuclear weapon. It just so happens that all of those other things are rare and earthquakes are fairly common. Also Tsunamis don’t have to occur in the ocean…they can occur in any large body of water.

Tsunamis are not actually surfable…in fact the characteristics of tsunamis are very similar to a low-to-high tide swing, albeit much larger and much more violent. In general the tsunami “wave” is moving much too fast and the swell period is measured in hundreds of miles, both of which do not allow the wave to take a “rideable shape”.




Tidal Waves (aka the tides)





Tidal Waves are the high and low tide that your beach experiences each day. These waves are caused by the gravity of the sun, the moon, along with the spin of the Earth in relation to those celestial bodies. The basics behind it is that there are 2 bulges of water in the ocean, one of which points to the sun, the other to the moon. As the Earth spins these bulges eventually get ran into land…as these causes them to reflect back and bounce all around the various ocean basins.


What is really crazy is that there are almost 200 different factors that have to be accounted for when you predict a high and low tide for a location. What is even crazier is that almost all of those factors are fairly stable so once you take them into account all you have to do is change the date on the forecast and the numbers fall into place. It is possible, though I am not sure why you would want to, to get a tidal forecast for a particular location 10, 20, or 200 years in advance…I guess it is probably something that oceanographers do when they are really bored.

These waves are also not-surfable but since the tide plays an important roll in surfing you definitely want to keep track of how it is behaving.



Wind Waves




Wind Waves are another properly named type of wave (I love some of the terminology in Oceanography, much of it is amazing straightforward). Winds waves are generated by wind blowing over the ocean. The more intense the wind, the longer the duration, and the bigger the area that the wind is blowing over, the bigger the wind waves will be.


These are the waves that we actually surf…from an energy/swell period perspective they are actually the weakest type of waves with the shortest swell periods…not that it matters much…a 20’ wave at Jaws can kill you just as fast as a tsunami.


Continued in these posts
Part 2: Wave Creation and Swell Generation
Part 3: Characteristics of swells
Part 4: Breaking waves

Ocean Science 101: South Pacific Island Shadowing

It is time for another installment of Armchair Forecasting 101. Where I give you random information about surf forecasting that will probably have zero impact on your ability to get waves but will make you a way more interesting conversationalist at parties.

In this post I will cover a term that you will probably see in a lot of my forecasts as we head into the spring, summer, and fall. This term is South Pacific Island Shadowing and is sometimes known as the Tahitian swell shadowing.

South Pacific Island Shadowing occurs for Southern California when we get SW swells that are coming in from a 205- to 220-degree swell angle. This shadowing process can greatly effect the size and consistency of a SW swell and is generally responsible for turning what should have been a great swell event into a mediocre (and sometimes very frustrating) one.

Swells generated in the South Pacific storm track that are approaching from these angles have to pass through a series of island chains on their path to SoCal. This is where the shadowing occurs.

You might ask “Hey I have been to a bunch of those islands…they are really small and far apart. How can they have such an impact on something as large and powerful as a swell?” Which would be a pretty good question.

In this case the answer is: It isn’t what you see above the surface that causes all of the problems but what is below.

A little Background info:
Swells are actually three-dimensional objects…but we spend a lot of time thinking about them in two-dimensions. Swell actually has a component of energy that extends “down” below the ocean surface. The longer the swell period the deeper this energy goes.

It is actually this “below the surface” energy that helps shape and facilitate the breaking waves that eventually hit our spots in SoCal. (I will go over the basics of this in another post…in the meantime you will just have to trust me.)

The thing to remember is that swells coming from the South Pacific end up having some very long swell periods (generally 16-17 seconds and longer), this is because they travel such long distances that much of the shorter swell period energy decays away leaving the more powerful long-period energy.

The Problem Occurs:
The problem occurs when this long-period energy moves through the island chains. Even though on the surface the islands are small they have a very well developed sea-mount supporting them…in fact there is, for all intents and purposes, an undersea mountain range underneath the island chains.

Long-period swells of around 18-seconds start feeling the sea-floor at about 850 feet…as they encounter the bottom they start to slow and change direction. If it was only a single obstruction this wouldn’t be a problem but there are hundred of overlapping islands spread over a couple thousand miles. It is sort of like sending the swell through a really messed up game of bumper pool.

The swell does eventually shuffle out of the other side of these islands but it is greatly diminished and has lost a lot of energy, both in size of the waves and the consistency of the sets.

What this means (or AKA why you should care):
Adam this is making my head hurt.

I know…it makes mine hurt too. I will sum it up for you.

If you see a big red blog on the swell model, but it is located in a position where the swell will pass through the South Pacific Island Shadow, then count on it being smaller and less consistent than if it had a clear shot.

Sometimes the swell models (like NOAA’s WavewatchIII) will “overcall” these swells, which in turn means that many of the surf forecast websites will overcall them too, (because their swell models are basically WavewatchIII with a different skin…).

The trick is to not to get caught up in the hype…yeah there is a swell coming, but it is likely going to be smaller and less consistent that most people think. Personally in these cases I start thinking about my free time…and is it really worth battling a horde of people to get inconsistent sets or should I save my time for a really good swell where I can get plenty of waves. It is usually a pretty easy call for me to make.

Anyway I hope this helps…I put together a cool graphic that will help illustrate the process and it shows both the open and shadowed swell directions for SoCal.