User:Jpanderson/first draft

Surf forecasting is the process of using offshore swell data to predict onshore wave conditions. It is used by millions of people across the world, including professionals who put their forecasts online, meteorologists who work for news crews, and surfers all over the world.

How Waves are Made
Waves are created as wind blows over the ocean, transferring its energy into the water The size of the swell is affected by three variables: the velocity of the wind, its duration, and its fetch, or distance the wind blows over.

Types of Swells
There are two different types of swell, groundswell and wind swell. Groundswell refers to waves generated far off of the coast, while wind swell refers to waves formed from local winds to the specific surf spot. . (In general groundswell produces waves that are much better for surfing.

Swell Data
There are three main factors used in surf forecasting: swell height, swell direction, and swell period.


 * Swell Height- Swell height refers to the height of the swell in deep water.


 * Swell Direction- Swell direction refers to the direction from where the swell is coming from. It is measured in degrees (as on a compass), and often referred to in general directions, such as a NNW or SW swell.
 * Swell Period- Swell period is an extremely important fact in surf forecasting that is often overlooked. It is a measurement of time between successive waves in seconds. If you multiply the swell period by 1.5 you will calculate the speed in knots of the waves. The swell period will give you information about how the swell will affect specific breaks differently.

Deep Water Travel
To accurately forecast the surf you need to understand what happens to the swell as it travels in deep water

Wave Decay
As the waves travel towards shore they lose energy and decrease in size. This size decrease is more than 60% in just the first thousand miles and a much slower rate after that. . “This wave decay is caused by the local waves dissipating rapidly once outside of the wind-generation area, directional spreading of waves as they move away from the storm at different angles and the separation of waves as they travel forward at different speeds after leaving the storm area.”

Swell Life Cycle
As a result of waves traveling at different speeds the longer period waves separate from the shorter period waves. The faster long period waves will arrive at the shore first. These waves, called forerunners, are smaller than the main body of swell and are important because they are a sign that the remainder of swell is soon to arrive.

Shoaling
As waves approach shallower water the bottom of the wave begins to feel the bottom of the ocean. This causes the wave to increase in size and become steeper. The wave becomes increasingly larger until it hits water that is approximately 1.3 times as deep as the wave, where it will begin to break. The shape of the ocean floor affects the break greatly. A gradual sloping ocean floor will result in a slower crumpling wave (better for long boarding) while a steeper sloping floor will result in a faster, hollower breaking wave (better for short boarding).

Wrapping and Refraction
One important fact about waves is that they focus more of their energy towards shallower water. Waves will always turn and refract towards shallower water. The longer the period of the swell the more it tends to wrap into a spot. Significant underwater irregularities, such as underwater canyons and seamounts, can also affect how the waves come into a surf spot. Irregularities like these may cause the surf to much larger at one spot near by, while almost nonexistent at another.