Warnings on rough waves
Wave height warnings refer to significant wave heights. Individual waves can be from one and a half to two times higher than the reading given in the warning.
Three risk levels are in use:
2.5 metres (yellow)
4 metres (orange)
7 metres (red).
The lowest warning level is in use from May to October. The other two levels for periods of up to 5 days are in use throughout the year.
When the significant wave height reaches 2.5 metres, sea traffic – for instance, the fast ferries between Helsinki and Tallinn – may be disrupted. However, it is good to remember that the significant wave height need not be higher than one metre to make boating more difficult.
Four metres is a rare wave height, for instance in the Gulf of Finland. Off Helsinki, there are on average ten hours a year when such wave heights are recorded.
In the Finnish sea areas, wave heights reach the highest risk level only in the Northern Baltic Sea and south-eastern part of Sea of Bothnia. Such wave heights can pose problems, or even danger, to the navigation of larger vessels as well.