There are usually quite a few people on the Kvarner from September to June.
From June to September the air temperature at Kvarner is perfect for sunbathing. The swimming season at Kvarner occurs from July to September, when the water is warm and comfortable for swimming.
In December, in June and in November and October Kvarner has rainy season. This is something to keep in mind when planning your trip since it is quite possible that you may be unable to sunbathe.