Surf Science: An introduction to swell formation, surf spots, and reading waves.

April 27, 2016

Surf Science is one of the weekly seminars that we offer here at WRSC. It is an informative presentation for all surf levels interested in wave formation, swell forecasting, and wave classification. For me, surfing is more than just riding waves. Surfing is about being connected with mother nature and being in tune with the perpetual flow of the ocean. Understanding the science of surf will make your sessions more worthwhile, and also give you a higher perspective of whats really going on out there. Enjoy!

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The photo on the left is a large, winter-time low pressure system that would give Hawaii upwards of 50ft waves. The photo on the right is how these waves would travel throughout the Pacific basin, eventually making their way to Costa Rica in the 4-8 foot range several days later. Basically, the friction between the wind and the ocean surface creates small disturbances called waves that can carry the wind’s energy for 1000’s of miles through open water.


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All of these factors are important, but the most important is the third factor, the distance over open water. For example, imagine that we have an Olympic-sized swimming pool at our feet. We apply 100 mph wind (force) for 72 hours (duration). But because the distance over open water is limited to a swimming pool, the waves will not get much bigger than a few inches. Apply this same scenario to 1000 miles over the Pacific Ocean, and now we are talking about some solid surf!

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The above model illustrates how waves continually grow as they travel over open ocean with 40 knot sustained winds at their backs. As the wave increases in height above the ocean surface, the wave is also growing below the ocean surface. For example, after 2000 miles of wind/wave creation, we have a 31 foot wave at 20 seconds with 1000 feet of downward energy. WOW!

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If you’ve ever taken a chemistry of physics class, you would know this term as wave frequency or wavelength. In surfing, we call this wave period and is measured in seconds between consecutive wave peaks. Wave period is very important because it tells us how far the wave has traveled, and how much energy the wave holds below the surface. For example: Imagine you drop a rock into a calm, glassy pond below your feet. Right where the rock makes impact, the water is chaotic and the ripples are very close to each other. As the ripples percolate away from the impact site, they begin to organize and spread out, creating distance between themselves. This is very similar to ocean waves. As the waves travel throughout the ocean, the seconds increase along with the downward energy. Therefore, the higher the seconds in the surf zone, the further the waves have traveled to reach the beach.

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This is an example of long-period waves reaching the coastline of Nova Scotia. Notice how the waves are nice, organized, corduroy lines until the horizon. These waves have traveled very far to reach the coastline and the surfers are reaping the rewards.

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Furthermore, the slope of the shoreline directly offshore will influence whether the wave is a smooth, easy,  rolling wave, or a top-to-bottom tubing wave.

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In a span of 24 hours, there are 2 low tides and 2 high tides in a diurnal tide pattern (what we have here in Costa Rica)

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Incoming tide is when the tide is rising. 95% of surf spots function the best with the incoming tide because of the cooperation of forces between the waves and the ocean. During the outgoing tide (dropping tide) we have the opposition of forces. This can make for less consistent sets, more current, and overall less power behind the waves.

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Wind Direction is always the X-factor in any surf session. Even if there is good-sized swell with the incoming tide, an unfavorable wind direction can ruin an otherwise epic surf sesh.

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Offshore winds are favorable for surfing. This is when the wind blows from the land to the sea. The wind blows against the face of the waves grooming them like a comb allowing for better-formed waves and (in some cases) big tubes!

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With it’s close proximity to Lake Nicaragua, Witch’s Rock (Roca Bruja) in Northern Costa Rica receives offshore winds up to 300 days a year. Certainly a world-class wave by any standards. Wanna go??

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Onshore winds are when the wind blows from sea to land. This wind is good for building wave heights (if strong enough) but bad for wave shape.

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Onshore winds make for sloppy surfing conditions and zero uniformity between waves. But can still be fun if you’re desperate enough..

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The type of surf spot really depends on what is going on under the ocean surface.

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Beach breaks are fairly straightforward. Basically, the wave comes from deep water onto a flat sand bank. Because there are no rocks or reef, beach breaks are generally the best option for beginner surfers. When you’re done with the wave, just put your feet down on the sand, and get ready for the next one! All of our surf lessons in the Beginner Surf Program are right out front at the Tamarindo beach break.

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Puerto Escondido on Mainland Mexico is quite possible the best beach break in the world. An underwater canyon offshore re-directs and magnifies the oncoming waves resulting in some of the highest quality waves on the planet breaking over a sandy bottom. VIDEO HERE

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Point breaks are basically thumbs in the coastline that waves will wrap around. Because the water is shallower next to the point, only one part of the wave will break at a time. You can get really long rides at point breaks to rapidly improve your surfing.

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Located in the Southern zone of Costa Rica on the Pacific side, Pavones is the second longest left-hand wave in the world. The wave wraps around a point and can offer rides up to a mile long! If you get the chance, you must surf this wave. VIDEO HERE

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Rock / Reef breaks are similar to point breaks in that the wave breaks uniformly over the shallower bottom. These are the most dangerous of the 3 spots because of the sharp bottom and are usually reserved for advanced surfers.

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One of the most well-known reef breaks in the world. The waves at Teahupoo come from very deep water offshore and explode on a shallow reef. VIDEO HERE

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The two types if swell depend on the origin of the storm and how the waves were created. Also, how far the waves have traveled to reach your beach

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This is an example if a ground swell for Costa Rica. This storm in the Southern Pacific is generating open ocean wave heights up to 36 feet. About 4 days after this moment, clean, 8-12ft ground swell will reach the beaches of Costa Rica. There will be no bad weather directly associated with this storm in Costa Rica, just the long-period ground swell. It is called Ground Swell because there is so much downward energy under the wave that the wave begins to feel the ocean bottom at about 1000 feet.

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This is an example of Wind Swell. Notice how the storm is directly offshore of the East Coast. There is not much time for the waves to organize into clean swell so the waves will arrive with shorter periods and sloppy, onshore conditions. This map features a winter-time low pressure system with it’s center located about 300 miles off the coast of New Jersey. Big waves for sure, but there would most likely be rain, wind, even snow. Makes you ask yourself…How bad do you want it?

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From the beach, it may look like this is wave is going to the right, but we always classify waves from the perspective of the surfer. If you were paddling into this wave, you would want to make a left turn when dropping into the wave.

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Same idea as above. This may look like the wave is going to the left from the beach, but if you were paddling into this wave, you would make a right turn when dropping in.

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This happens when there is neither a left or a right. The wave comes in as a big wall of water and breaks without a clean shoulder to ride. Closeouts are a common problem with beach breaks.

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Disregard the wave in the back. Focus on the fat wave in front. Fat waves occur when the water is just barley shallow enough for the wave to break. The wave doesn’t really jack up, but just feathers at the top. Fat waves are fun for longboards and perfect for learning.

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Crumbly waves are in-between fat waves and tubing waves. These waves are good for high-performance surfing because they usually have a nice steep face, but not too much consequence if you fall. This photo is of Trestles in San Clemente California. One of the best, crumbly waves in the world.

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Tubing waves! These are high risk, high reward waves reserved mostly for advanced surfers. The ultimate feeling in surfing it to be able to pull into the tube and then ride out cleanly. Tubing waves happen when there is a dramatic slope leading up to the shoreline.

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An finally, if you want to track and forecast the waves for yourself, these Surf Resources should come in handy.


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