21 
when the northerly onshore storm strikes the southern coastal waters, marks the beginning 
of the wind set-up. This phase is sometimes preceded by a temporary lowering of sea levels 
due to strong alongshore to offshore prefrontal winds. 
Storm surges generated by the above meteorological pattern were, e.g., the wind set-up on 
25-26 December 1976, 29-30 November 1988, 1-4 January 1995, and 3-4 November 1995. 
5.2 Stormy low pressure centre moving across the Baltic Sea 
A rather large proportion of the low-pressure systems generating storm surges and wind set 
up at the southern Baltic coasts track across the Baltic Sea between approximately 60 e N 
and the southern coast. While such low-pressure centres cross the Baltic basin, they are 
preceded by offshore winds on the southern coasts, and as they move eastwards, onshore 
winds follow in their rear. The rather regular, circular wind distribution around the storm 
centre is usually modified by a system of atmospheric fronts which is connected with the 
centre. Depending on the track of the low-pressure centre - across southern Sweden, across 
the southern basins of the Baltic Sea or across land along the southern coasts - its passage 
has different effects on the different coastal sections. 
a) With a low-pressure centre travelling across southern Sweden, the southern Baltic coasts 
come under the influence of southerly winds. Very strong winds, which are frequent in 
this area, may initially lead to rapidly falling sea levels. Winds on the southern Baltic 
coasts will only veer onshore when the depression has moved farther east and the 
atmospheric front has crossed the coastline. The change to N - NE wind directions may 
be very sharp, with an immediate and violent impact on the coastal waters. In the western 
parts of the coast, the increase in wind speed begins earlier and the wind setup occurs 
earlier (by a few hours) than farther east. 
b) With a low-pressure centre travelling across the southern basins, SW - SE winds prevail 
initially in the coastal zone. This may be followed by a brief calm after which NE winds 
increase rapidly to gale force and, veering SE - SW, may develop into a strong westerly 
(alongshore) storm lasting several hours, after which the winds veer sharply NE - N. In 
the event of the atmospheric front (the shift line of wind directions) overlying the 
coastline, the sequence of wind directions, and hence of the different storm surge 
phases, may deviate from the normal pattern. Also sea levels may culminate or fall later 
than usual. 
c) With a low-pressure centre moving across land close to the southern coast, the fetch of 
strong SE - SW winds does not extend across the coastal waters, and the SE - E winds 
in front of the depression influence only a limited area over the southeastern basins, 
causing water levels to sink rather slowly or not at all. At the rear of the depression, a NE 
- N storm causes sea levels to rise rather rapidly, starting in the western parts of the 
coast. As the depression advances east, all sections of the southern coast are affected 
successively by the storm surge. However, the culmination of wind setup on the eastern 
coasts may occur several hours later than in the west.