So What Makes Ocean Waves?
The wind blowing creates a disturbance on the ocean surface, creating ripples. As the wind continues to blow, the ripples turn to chop. This chop begins to gather speed. As these wind chops are moving they combine to make larger wind chops picking up yet more speed. These wind chops in turn combine and turn into what we call wind waves.
Within a storm there are a lot of different waves going in different directions with different wave periods and wave heights. This is called the Sea State.
This distance between waves is called Wave Length.
The time in seconds between consecutive wave crests as they pass a certain object such as a buoy in the ocean is called Swell Period.
As these waves combine with one another they grow larger and the distance between them becomes greater and their energy grows. This energy is being transferred downward below the ocean surface. The more energy a wave has the deeper it reaches into the ocean. This is important to note because the depth of energy will eventually effect how the ocean waves we ride break.
Once the waves break free of the storm, either by the storm dying or the speed of the waves exceeds the speed of the storm, the wind chop and shorter period wind waves dissipate and the energy that survives is what we call Swell.
Surfers generally categorize swells into two groups
- Wind Swell
- Ground Swell
Wind Swells are generally considered anything under a 11 second period. These are short period swells.
These are swells that are generated by winds fairly close to shore, local winds within a couple hundred miles from land.
Wind swells do not have a lot of time to travel so they are closer together and its energy is focused more towards the ocean surface.
Since these swells are formed so close to shore they do not have a chance to shed much of the wind chop still associated with it. Swell period is a significant factor in regards to how an ocean wave will break once reaching the coast.
4ft @ 15 seconds ground swell will more often than not be better then a 7 ft @ 7 seconds wind swell
Ground Swells or Long Period swells will range in the 12-25 seconds range. Long period waves move faster and its energy runs deeper.
They are called ground swells because as they approach the coast their energy reaches down onto the ocean floor, that will than lead the wave to behave in certain ways.
These swells are the ones generated far out to sea and can travel great distances all the while maintaining a good amount of their original energy.
So What Determines The Size Of Ocean Waves.
- Wind Velocity-Speed of the wind measured in knots.
- Wind Area (Fetch) Amount of ocean surface area affected by wind blowing in the same direction.
- Duration Of Storm- The amount of time those winds blow over the same part of the ocean.
The harder the wind blows, the longer the time it blows and the greater the distance it blows, the bigger the waves and longer the swell periods. The longer the swell period, the stronger the swell.
One will hear surfers refer to sets when speaking about waves, what are these?
These are individual ocean waves/swell that are moving at nearly the same speed, keeping pace with one another to form a group or wave train. These groups are called sets when they reach the coast and break.
Swell Direction/Swell Angle
You will hear this term thrown around when talking about a swell hitting the coast; swell direction is the angle a swell originates from relative to a fixed location, wherever your local beach is at. Swells coming to your beach from due north (and are therefore heading south) are said to be coming from 0 degrees. Swells coming from due east and heading due west are coming from 90 degrees. Swells originating from due south and heading north are coming from 180 degrees, and so on around the 360-degree compass.
Each beach or surf break has a different swell window that is optimal for receiving swell.
So once swell is created and heading towards the coast what determines why and how it will break at your beach?