Wave measurements in the sea areas around the Finnish coast have been made since the 1970's, first by the Finnish Institute of Marine Research and now by the Finnish Meteorological Institute. Even if the Baltic Sea is small compared with the oceans, it is able to generate waves of respectable heights. The highest waves in the Baltic Sea are common during storms in the big oceans, but higher waves rare even there.
The biggest basin of the Baltic Sea, the Baltic Proper, has the most severe wave climate in the Baltic Sea. During the storm Rafael on 22 December 2004, the significant wave height in northern Baltic Proper reached 8.2 metres and the highest individual wave height was 14 metres. During the storm Toini January 12th 2017 a similar significant wave height (8.0 m) was recorded. The former record at the measuring station was 7.4 metres, which was measured twice in December 1999. During storm Gudrun on 9 January 2005, the significant wave height was 7.2 metres. Significant wave heights over 7 metres have been measured in January 1984 at Almagrundet near the Swedish coast and in October 2009 and in February 2011 in the southern Baltic Proper (Sveriges meteorologiska och hydrologiska institut, SMHI).
The highest measured significant wave height off Helsinki in the Gulf of Finland is 5.2 metres. It was measured first time during a south-westerly storm on 15.11.2001 and the highest individual wave reached approximately 9 metres. A significant wave height of 5.2 metres was measured a second time off Helsinki as easterly winds blew during a storm called Antti in 2012. At this location, both easterly and westerly winds are able to generate waves this high, but they are not expected to grow much higher due to the narrow shape of the Gulf of Finland.
The wave height measurements in the Central Bothnian Sea began in 2011. During the storm Tapani on 26 December 2011 the highest significant wave height, reaching 6.5 metres, was measured in the Central Bothnian Sea. The earlier record high significant wave height, 5.5 metres, was measured in the southern Bothnian Sea in 1970s.
The highest measured significant wave height in the Bay of Bothnia is 4.4 metres. It was measured during storm Eino on 17 November 2013 and the highest wave was approximated to be roughly 8 metres. The wave observations in the Bay of Bothnia continued after a thirty year interruption in 2012; the previous record height of 3.1 metres was measured closer to the shore.
The longest measurement time series are from the Northern Baltic Proper and from the Gulf of Finland. In the other areas the measurements have been made during shorter periods. The wave measurements are also local: higher significant wave heights than mentioned above are possible in the Baltic Sea. The highest modelled significant wave heights in the Baltic Proper are 9.5 metres.
The wave height records are determined based on the significant wave height. The highest individual wave is nearly twice as high as the significant wave height. The reported highest individual waves are not based on direct measurement, but are statistically estimated from the significant wave height.