Cross sea

A cross sea (also referred to as a squared sea or square waves) is a sea state of wind-generated ocean waves that form nonparallel wave systems. Cross seas have a large amount of directional spreading.[1] This may occur when water waves from one weather system continue despite a shift in wind. Waves generated by the new wind run at an angle to the old.

Cross swell at Île de Ré.
Aircraft view of cross sea near Lisbon.

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 create 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.[2] Vessels fare better against large waves when perpendicular to the waves. In a cross sea, vessels are more likely to be struck in a dangerous way.[3]

A cross swell is generated when the wave systems are longer-period swells, rather than short-period wind-generated waves.[4]

See also

References
  1. "Cross Sea". Glossary of Meteorology. American Meteorological Society. Retrieved 4 Feb 2019.
  2. Toffolia, A.; Lefevre, J. M.; Bitner-Gregersen, E.; Monbaliu, J. (2005). "Towards the identification of warning criteria: Analysis of a ship accident database". Applied Ocean Research. 27 (6): 281–291. doi:10.1016/j.apor.2006.03.003.
  3. Xiaoming Li. "Is the Cross Sea Dangerous?". Wayback machine. Archived from the original on 2014-05-03. Retrieved 10 February 2019.
  4. Bowditch, Nathaniel (1995). "Glossary C" (PDF). The American Practical Navigator. Bethesda, MD: National Imagery and Mapping Agency. p. 758. ISBN 0-403-09895-5.


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