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A cross sea (also referred to as a squared sea or square waves) is a
A cross sea (also referred to as a squared sea or square waves) is a sea state
In oceanography, sea state is the general condition of the free surface on a large body of water—with respect to wind waves and Swell (ocean), swell—at a certain location and moment. A sea state is characterized by statistics, including the ...
of wind-generated ocean waves that form nonparallel wave systems. Cross seas have a large amount of directional spreading. This may occur when water waves
In fluid dynamics, a wind wave, water wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result from the wind blowing over the water surface. The contact distance in the direction of ...
from one weather system
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...
continue despite a shift in wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...
. Waves generated by the new wind run at an angle to the old.
Two weather systems that are far from each other may create a cross sea when the waves from the systems meet at a place far from either weather system. Until the older waves have dissipated, they can present a perilous sea hazard.
This sea state is fairly common and a large percentage of ship accidents have been found to occur in this state. Vessels fare better against large waves when sailing directly perpendicular to oncoming surf. In a cross sea scenario, that becomes impossible as sailing into one set of waves necessitates sailing parallel to the other.
A cross swell is generated when the wave systems are longer-period swells, rather than short-period wind-generated waves.
Notes
References
{{physical oceanography Water waves