A variable summer in sea areas

In July and in early August, the surface temperature of sea water in the coastal areas of the Gulf of Finland was clearly higher than average. In late August, the sea gradually begins to cool.

Photo: Eija Vallinheimo

According to the Finnish Meteorological Institute’s measurements, the past summer in Finnish coastal areas was variable. In early June, sea water temperatures rose quickly, reaching the season’s highest readings for a decade, 18–20° C, in some places. However, upwelling soon brought the rise in temperatures to a halt, and surface temperatures fell locally to as low as 6° C within a couple of days. In the course of upwelling, winds blow the warm surface water near the shore out to the open sea. This water is replaced by cold water rising from the depths to the surface. Owing to upwelling, water temperature can drop very rapidly.

In the Gulf of Bothnia, the temperature of sea water in early July rose quickly back to the readings measured in mid-June. However, new upwelling cooled the water almost equally quickly. In the Gulf of Finland, temperatures kept rising until mid-July. In the Gulf of Bothnia, too, the impact of upwelling was short-lived and the temperature started to rise again until mid-July, exceeding 20° C.

Average temperatures attained in mid-August

The Institute’s measurements reveal that, in July and early August, the surface temperatures of sea water in the coastal areas of the Gulf of Finland clearly exceeded the average temperatures, reaching as high as 22° C. The situation was normalised again by mid-August.

In the Archipelago Sea, surface temperatures remained somewhat steadier than in other sea areas, but even there the temperature rose higher than normally, to about 20° C in mid-June and early July. The warming came to a rapid halt because of upwelling; thereafter, temperatures remained typical for late July and early August, at about 18–19° C.

After mid-August, surface temperatures returned to the average readings measured during the past decade: on the coast of the Bay of Bothnia to about 16° C and elsewhere to about 18° C. At the end of July, very strong upwelling in Raahe and Pietarsaari, on the coast of the Bay of Bothnia, caused surface temperatures to drop by nearly 10 degrees within a couple of days. During August, temperatures have still risen slightly from some of the lowest readings for the past decade. At about 14° C, they are now close to the average temperatures. The sea gradually begins to cool in late August.

Additional information:

Pekka Alenius, Leading Research Scientist, tel. +358 50 439 2887, pekka.alenius@fmi.fi

Sea surface temperature forecast:http://en.ilmatieteenlaitos.fi/sea-temperature-forecast