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A wave model is a depiction of how high waves are, where they are heading, and how swell patterns are propagating throughout the world. One type of model represents the height of waves, and another type shows the timing between each wave swell. Data are derived from ocean buoys as well as weather observations and forecasts, and from satellites. Ocean waves are complex and hard to forecast in all situations, but mariners can use a wave model to get an idea of the wave conditions for certain areas at specific times.
Color is usually used to show the state of the ocean. Red shades typically indicate areas where waves are high and the sea is rough, while shades of blue and purple show relatively calm seas. Concentric circles can also be used to indicate areas where the wave height is the same. Sea height charts also have arrows, called sea vectors, to tell what direction the waves are going in or are expected to be based on weather forecasts.
Arrows used on a wave model to show swell period are known as swell vectors. Based on the time period, such maps show an average maximum time for swells depending where the mariner is located. Differences in swell periods happen as waves generated by wind travel away from storms, and the model depicts where such waves congregate such as in swell fronts. This gives sailors an idea of how long rough seas will last, and surfers an estimate on how long waves will be optimal for riding.
The weather is the main factor for ocean waves, but so is physics. A wave model also takes into account things like the relationship between moving waves and the overall body of water. Objects are moved by a wave in a general circular motion, defined mathematically as a trochoidal curve below the wave peak. The ratio of wave height and length also factors in to how waves travel and interact.
Data from the tracking of storms are input into wave models as well. It is easier to predict wave characteristics for large-scale storms, but most computer models do not pick up as well on what happens with a hurricane. Tropical systems are smaller and less predictable, so forecasting the state of the sea in advance is hard to do even with a wave model. Weather forecasting agencies produce such models twice each day, with some forecasters giving a three day prediction, while others predict up to a week.