Tonitru Isles

The Tonitru Isles (known colloquially as the Storm Islands) are a large archipelago situated north of Velen and West of Athkatla. The Sword Coast shipping lanes avoid them due to unpredictable sailing conditions caused by terrible weather and volcanic activity on the sea bed.
It's unclear whether the islands are easier to approach from the west, so they may be inhabited.
Local sailors recently witnessed a large volcanic eruption on one of the islands. This appears to have settled the sub-nautical activity and had a knock on effect of reducing the ferocity of the storms. A few local captains have started to explore the islands.