On this page of the Witcher 3 Wild Hunt guide, you will find a map of enemies encountered on the Southern Isles from the Skellige archipelago. The different colors on the map indicate the threat level of enemies in the area. Thanks to this, we can avoid problems with stronger opponents from the South Islands, if Geralt is not yet strong enough.
Southern Isles: enemy levels
The map above shows Southern Isles that are a part of the Skellige islands archipelago. Places where you will find enemies on specific levels have been marked on the map. Some of them are constantly on the move and because of that the territories shown should be considered as approximate. Recommended character level for exploring this location is 13.
In the South Islands, the only threat are sirens. They appear when swimming between the islands. Dealing with sirens shouldn't be a problem for a medium-developed Geralt.