Weather in the Baltic
Much of the following has been culled from The Admiralty Pilots and a World Meteorological Organisation publication - The Climate of the Baltic Sea Basin. As a general point, the Pilots are, to my mind, the most complete and easy to use source available for meteorological information. Despite or, probably because of, their very formalized, dry-as-dust format they are easy to use and contain all the information that a sailor really needs.

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 General weather Patterns

 Winds

 Temperatures

 Sea Temperatures

 Fog

 Currents

 Sea State

General Weather Patterns

  
 Rather like the British Isles there is no such thing as a typical Summer in the Baltic. Much depends upon the behaviour of the Azores High. When this extends far enough toward the British Isles and Northern Europe then long fairly settled periods can occur. Atlantic low pressure areas tend to get pushed north-eastwards towards Iceland. Their occluded fronts then move towards and often across the area However, the Baltic is a long way from the high and, quite frequently, a slight receding of the high allows secondary depressions form, typically near the Skagerrak. These secondaries often appear to be in families of 3 or so and tend to move east and progressively south of east although tracks can be erratic.

After the Winter season, with its frequent extensions westwards of the Siberian high, the wind patterns become weak and rather ill defined in May but, thereafter, the frequency of eastwards moving depressions increases although few are particularly deep. A more definite westerly regime ensues through the Summer season although there can still be, as for the UK, longish periods of settled anticyclonic weather.

 

Winds
During April and May winds are very variable in direction, not particularly strong. Little sensible can be said about prevailing directions. Through the Gulf of Finland winds tend to be channelled by the Gulf ie to be ENE or WSW. To the south of Gotland directions between south and east are comparatively rare. In the Copenhagen/Kiel area there is some tendency toward west to south-west. Average wind speeds are around 10-12 knots in April and more like 10 in May.

Sea breezes are common, developing around midday. Offshore, land breezes are relatively rare.  Through June to August the tendency over the open sea is more towards winds from a westerly point and for some increase in average strength to 12 knots generally and up to 14 in the Kattegat and near Rostock. Near the coast, sea, sea breezes dominate after midday. These will be from a Southerly oint up the Swedish coast and a northerly point down the Finnish coast.

Winds in of Force 5 or more occur on about 15%, 24% and 49% of occasions in the Spring, Summer and Autumn respectively.
 

The table below shows percentage occurrences in ( ) and numbers of days when winds Force 6-7 and Force 8 or more occur month by month (although winds of more than Force 8 are virtually unknown during the Summer months).
Month April May June July August
Wind Percentage in ( ) and No  of Days
F  6 - 7 (14)

4

 (12)

4

 (12)

4

 (16)

.5

 (17)

5
           
F  8 + (1.8)

<1

 (0.7)

<1

 (1.6)

<1

 (1.6)

<1

 (2.5)

<1

 

Temperatures

 
Over the sea, the air temperature is dominated by the sea temperature which, in the late spring is dependent upon the melting of the Winter ice. By July air temperatures reach 16 or 17 deg C rising to 22 deg near mainland coasts. Day time temperatures over land can, on occasion, be as high as 30 deg C. The following table shows some typical daily maximum temperatures and the average monthly average extremes. Also shown are average minima over land and number of number of days of rain (defined as at least 1 mm).
Place Month Ave Daily Max
Temp Deg C		 Ave Monthly Max
Temp Deg C		 Ave Daily Min
 Temp Deg C		 Number of days with
 >1mm rain
Copenhagen April 10 19 3 9
  May 16 23 7 8
  June 19 26 11 8
  July 22 27 13 11
  August 21 26 13 5
           
Rostock April 11 23 3 9
  May 17 27 7 8
  June 19 28 10 9
  July 22 30 13 8
  August 21 29 13 10
           
Tallin April 9 19 1 7
  May 15 24 5 8
  June 19 27 10 8
  July 21 28 12 8
  August 20 27 11 6
           
Helsinki April 8 17 0 11
  May 16 25 4 5
  June 19 26 9 5
  July 22 26 12 5
  August 20 26 11 6
           
St Petersburg April 9 21 2 9
  May 16 25 7 9
  June 20 27 12 6
  July 22 28 14 6
  August 20 28 13 6
           
Stockholm April 9 19 0 7
  May 16 24 5 7
  June 19 26 10 7
  July 22 28 13 10
  August 21 26 12 5

Sea Temperatures
In the late Spring and Summer, following the ice melting, sea temperatures rise rapidly. Around the Danish islands and in the Southern Baltic near Kalinigrad, 10 or 11 deg C in May becomes 17 to 18 by August. To the south of Gotland  tempertures of 5 or 6 in May becomes about 16 degrees in August. In the Gulf of Finland a temperature average of just 1 deg C in May rises to 16 or higher approaching St Petersburg in August.

Fog and Thunder
Fog is most frequent over the open sea in April and May while the seas are still cold but the air temperature is rising. In March and April, fog frequencies are around 25% near the Southeast of Sweden and near the South of Gotland and 10% elsewhere. During July and August the frequencies are around 10% and 2% respectively. To read more about fog  click here Thunderstorms are likely during any time of the year. Typical numbers of days per month during May to August with thunderstorms range from 2 or 3 at Copenhagen and Stockholm to 4 or 5 towards the east near Riga, St Petersburg and Helsinki.

Sea Currents
The average currents are very weak. They are driven largely by the flow of water from rivers into the Baltic and by the ice melt. The evaporative effect, that creates the easterly surface current through the Strait of Gibraltar into the Mediterranean, is relatively weak in these latitudes. The net result is a flow out of the Baltic through the Kattegat. In the Gulf of Finland, there is a weak current  eastwards along the southern coast and a returning westerly along the north coast. In the Gulf of Bothnia, similarly, there is a north going current up the east side and a south going current down the Swedish coast. These currents are typically about ¼ to ½ knot.

Not surprisingly, there can be large local variations through channels, between islands and when there have been strong winds.

Tides, Waves and Swell
There is virtually no rise and fall of tide in the Baltic. A range of about 0.3 metres in the Kattegat becomes virtually zero further east. Sea levels do vary but this is as a result of air pressure (see the note on the CA Members Weather Pages), wind stress and the flow of water from rivers and melting ice.  See another page of this site for the effects of atmospheric pressure on sea levels.

There can be relatively short lived swells generated by strong winds but, otherwise, wave heights will depend mainly on the local winds.

Frank Singleton

18 November 1999


This page was produced initially for the Cruising Association Millennium Cruise to the Baltic


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© Frank Singleton, February 2000

 2 February 2000