57 
Fig. 6.16.2. Pressure pattern over Europe and wind field over the Baltic Sea on 15 April 
1997, 06 UTC 
Hydrological response of the sea level 
On 10 April, water levels were close to the mean sea level. However, towards the end of the 
day and early on 11 April, in response to a vehement W - SW offshore and alongshore storm 
over the western basins, water levels in the area dropped to 472 cm in Wismar, and 484 cm 
in Warnemünde on 11 April at about 06 UTC. As the central parts of the coast were not 
affected by the direct impact of the SW storm, sea levels in Swinoujscie and Kotobrzeg fell 
only slightly in the early hours of this day. As soon as the minimum had been reached shortly 
after 06 UTC, sea levels on the western coast began to rise following a rapid change of wind 
direction, with gale-force winds behind the cold front now blowing onshore (Fig. 6.16.3.). In 
the central part of the coast, the increase was slower and began about two to three hours 
earlier. 
The warning level of >560 cm was first exceeded in Kotobrzeg at 11 UTC, Swinoujscie at 14 
UTC, Sassnitz at 16 UTC, Warnemünde at 19 UTC, and Wismar at 20 UTC on 11 April. 
The maxima were reached very soon, between 17 and 23 UTC on 11 April. They exceeded 
the mean sea level by 1.0 -1.2 m and were as high as 620 cm in Wismar, 609 cm in 
Warnemünde, 604 cm in Sassnitz, 600 cm in Swinoujscie, and 612 cm in Kotobrzeg. 
The strongest surge dynamics were recorded by water gauges in the western part of the 
coast, where the culmination was recorded only 3 - 4 hours after warning levels had been 
exceeded. The maximum rate of increase was 52 cm/h in Wismar, but only half that rate was 
recorded in Warnemünde and Sassnitz, at 25 cm/h and 26 cm/h, respectively. The mean 
rates of increase were 19 cm/h in Wismar, 17 cm/h in Warnemünde, and 16 cm/h in 
Sassnitz. 
In the Pomeranian Bight and farther to the east, the surge dynamics were less pronounced 
although warning levels in this area were exceeded earlier than in the western parts of the 
coast. The increase was slower, with culmination in Swinoujscie reached 5 hours after 
warning levels had been exceeded, and in Kotobrzeg after as much as 10 hours. The 
maximum rate of increase was 25 cm/h in Swinoujscie and 22 cm/h in Kotobrzeg, with a 
mean rate of increase of 11 cm/h and 6.4 cm/h, respectively. Sea levels remained above 560 
cm for 22 hours in Swinoujscie, and 27 hours in Kotobrzeg. The decrease was smoother than 
that recorded by water gauges in the western part of the coast. 
The second rise of sea levels during these five days was preceded by a brief drop of water 
levels on the western coasts in the afternoon of 13 April due to an offshore SW gale, with the