The United States Wave Height image shows the expected wave height for coastal areas for the current day. Ocean surface waves are surface waves that occur in the upper layer of the ocean. They usually result from wind or geologic effects and may travel thousands of miles before striking land. They range in size from small ripples to huge tsunamis. There is little actual forward motion of individual water particles in a wave, despite the large amount of energy and momentum it may carry forward.
The great majority of large breakers one sees on an ocean beach result from distant winds. Three factors influence the formation of "wind waves":
- wind speed
- distance of open water that the wind has blown over; called fetch, and
- time duration the wind has blown over a given area.
All of these factors work together to determine the size and shape of ocean waves. The greater each of the variables, the larger the waves. Waves are characterized by:
- Height (from trough to crest),
- Wavelength (from crest to crest),
- Period (time interval between arrival of consecutive crests at a stationary point),
- Wave propagation direction (with respect to north).
Waves in a given area typically have a range of heights. For weather reporting and for scientific analysis of wind wave statistics, their characteristic height over a period of time is usually expressed as significant wave height. This figure represents the average height of the highest one-third of the waves in a given time period (usually chosen somewhere in the range from 20 minutes till twelve hours), or in a specific wave or storm system. Given the variability of wave height, the largest individual waves are likely to be about twice the reported significant wave height for a particular day or storm.