Rogue waves are large, unpredictable, and dangerous. Rogue waves (also called 'extreme storm waves') are those waves which are greater than twice the size of surrounding waves. They often come unexpectedly from directions other than prevailing wind and waves. Many reports of extreme storm waves describe them sudden "walls of water." They are often steep-sided and associated with unusually deep troughs. Some rogue waves are a result of constructive interference of swells traveling at different speeds and directions. As these swells pass through one another, their crests, troughs, and wavelengths sometimes coincide and reinforce each other. This process produces large, towering waves that quickly form and disappear. If the swells are traveling roughly in the same direction, these massive waves may last for several minutes before subsiding. Rogue waves can also form when storm swells move against a strong current, resulting in a shortening of the wavelength and increasing it’s amplitude. Large rouge wave of this kind are frequently experienced in the Gulf Stream and Agulhas currents (Figure 10.24).
Figure 10.24. This 60 foot rouge wave threatened a ship in the Gulf Stream near Charleston, South Carolina. Rogue wave have sunk ships, destroyed drilling rigs, and are responsible for many deaths and injuries along coastlines.