On 12 January 2017 an intense low generated record high waves in northern parts of the Baltic Sea. Waves up to 14 m were observed, equalling the previous record from December 2004.
By Linnea Rehn (SMHI)
On 10 January a wide low pressure system was located over the Norwegian Sea and a large high was located over Eastern Europe. This synoptic situation was responsible for a southerly to southwesterly wind over the Baltic Sea.
A secondary low over the North Sea deepened in the morning of 11 January and then moved northeastward over Scandinavia in the following 24 hours.
The Meteosat-10 Airmass imagery from 11 January 06:00 UTC, overlaid with the 1000 hPa fields (Figure 1, top right, click to expand), shows the position of this partial low — the red area represents dry descending stratospheric air.
The ASCAT 25 km from Metop-A (Figure 2) shows wind speeds of about 40–45 knots on 11 January at 19:40 UTC over the central part of the Baltic Sea (Figure 2).
The record high waves were observed by a buoy managed by the Finnish Meteorological Institute a few hours after midnight (Figure 3). Figure 4 shows that Jason-2 measured a significant wave height of 22.18 feet at 05:40 UTC near the Finnish buoy, which corresponds to about 6.8 m. The red star in the figure indicates the approximate position of the buoy.
The high seas which occurred over the Baltic Sea on 11 and 12 January were very unusual, but the development of the storm low that affected the Baltic Sea was actually quite normal and it did not generate unusual high wind speeds over the Baltic Sea. Yet, despite this, record high waves were recorded.
This small but intense low enhanced the southerly-southwesterly wind over the Baltic Sea and overnight, 11-12 July, the wind increased from strong gale to storm force.
Significant Wave Height
12 hour collection of Altimeter Wave Heights
There are a lot of conditions for parameters that have to be met in order for significant waves of about 8 m to build up over the Baltic Sea.
Due to the main low over the Norwegian Sea, a southerly-southwesterly wind was blowing over the Baltic Sea for at least 36 hours, and, for the last few hours before the record wave height was recorded, the wind speed increased to about 40–45 knots.
The direction and duration allowed the wave height to build over a long distance — from the coast of Poland to the Archipelago Sea, east of Åland. So, in other words, the long fetch made it possible for the record wave to build.