37 
Fig. 6.7.1. Route of the stormy low-pressure centre between 19 October and 21 October 12 
UTC; pressure pattern and wind field over the southern Baltic Sea on 21 October 1986 at 06 
UTC 
Hydrological response of the sea level 
On 20 October, water levels in the western part of the southern Baltic coast rose gradually 
from low values at the beginning of the day to mean levels later in the day, while in the 
central part they oscillated slightly around the mean levels. 
In the westernmost part of the coast, at about noon, offshore winds in front of the 
approaching stormy depression caused sea levels to fall slightly, after which they rose again 
somewhat when the centre of the low reached the water gauges during the afternoon. Levels 
then rose quickly when the wind shear line (the occluded front) passed southward and the 
onshore N - NW storm struck the coast. At 21 UTC, the level at Wismar rose more than 1 m 
in one hour, probably due to the impact of a so-called long wave (formed along the wind 
shear line and moving together with the progressing atmospheric front). The peak value of 
619 cm was recorded at 00 UTC. Levels then dropped a little and, in the field of the slightly 
weakening onshore storm, fell to normal values within a few hours. 
Similar changes of sea levels were recorded in the central part of the coast, where a time lag 
of 6-9 hours was observed. At first, between 12 and 19 UTC on 20 October, sea levels fell 
slightly (by about 40 cm) in Swinoujscie and Kotobrzeg due to the impact of the offshore 
southeasterly storm in front of the approaching low. The increase began about midnight, the 
rate of growth being at first moderate and considerably higher lateron. The maximum 
recorded in Sassnitz between 02 and 05 UTC on 21 October was flat. In Swinoujscie, the 
maximum was sharper and reached 590 cm, with a culmination between 6 and 7 UTC. In this 
part of the coast the maximum hourly increments were considerably smaller than in the west: 
22 cm/h in Swinoujscie and 54 cm/h in Kotobrzeg. Relative to the reference level indicator 
(509 cm on 19 October), the duration of this surge ranged from 15 hours in Wismar to 24 
hours in Sassnitz.