In the north-eastern Baltic the risk of meeting the highest waves is greatest, since strong south-westerly winds are common and they have the longest wind fetch. High seas can start to build up south of Gotland. On the west coast the highest significant wave height was 7,7 meter and the maximum wave height 13,0 meter outside Väderöarna 14 januari 2007.
Extremely high rogue waves have always been reported by sailors but it is only during the latest 15 years that it has been possible to observe and monitor these monster waves. There is no simple explanation other than that the energy from several wave systems combines on unique occasions into one large wave. Monster waves have a short lifespan.
According to the Guinness Book of Records, waves with a height of 24 m were observed in the northern Pacific by the USS Ramapo on the night of 6-7 February 1933, when the average windspeed was 35 m/s.
The highest measured wave was 26 m observed by the ship Weather reporter in the Atlantic at 59° N 19° W on 30 December 1972.