Rogue Wave

Primary reference(s)

WMO, 2018. Guide to Wave Analysis and Forecasting, WMO No. 702. World Meteorological Organization (WMO). Accessed 12 August 2019.

Additional scientific description

Rogue waves, called ‘extreme storm waves’ by scientists, are those waves which are greater than twice the size of surrounding waves. They are very unpredictable, and often come unexpectedly from directions other than those of the prevailing wind and waves. Since these waves are uncommon, measurements and analysis of this phenomenon are extremely rare (NOAA, 2019).

Metrics and numeric limits

Not identified.

Examples of drivers, outcomes and risk management

Exactly how and when rogue waves form is still under investigation, but there are several known causes.

• Constructive interference: Extreme waves often form because swells, while traveling across the ocean, do so at different speeds and directions. As these swells pass through one another, their crests, troughs, and lengths sometimes coincide and reinforce each other. This process can form unusually large, towering waves that quickly disappear. If the swells are travelling in the same direction, these mountainous waves may last for several minutes before subsiding (NOAA, 2019).
• Focusing of wave energy: When waves formed by a storm develop in a water current against the normal wave direction, an interaction can take place which results in a shortening of the wave frequency. This can cause the waves to dynamically join together, forming very big ‘rogue’ waves. Currents where these are sometimes seen include the Gulf Stream and the Agulhas Current. Extreme waves developed in this fashion tend to be longer-lived than those formed by constructive interference (NOAA, 2019).

A good knowledge of the extreme wave environment and related wave/structure interactions is required for the design of safe and economic offshore structures and ships (Clauss, 2002).