Out of Synch.
The Baltic Sea and the Kattegat are very small bodies of water and until recently not considered to produce any surf-able waves (at least by outsiders). The only source stirring up these waters are local winds and it doesn´t help that the Baltic Sea is generally very shallow. But the WWW has seen a constant flux of pictures of very decent surf during the past few years which slowly convinced northern European surfers to believe what Danish and Swedish surfers already knew: yes, there is surf in this seas and in can get damn good.
The main reason for this unexpected quality waves is the rugged coastline in particular in Sweden. There are myriads of bays and points and reefs and by the sheer number of set ups with wave creating potential it is just a question of statistics to understand that there are quite a few places that can transform the wind-swells into surf-able waves while protecting them from too much wind from the wrong direction.
But the limited size of these seas in general only allows short lived wind-swells with a maximum period of 5 to 6 seconds. This means that the swells do not transport a lot of energy and lose power very quickly when getting bent by the coastline. It also means that the swells will vanish very soon once the wind turns down.