Rognan: when to go? Whether you love the heat or the cold, if you're planning a trip here, it could be useful for you to know: July, has temperatures that can reach 13°C, it's the hottest month at this touristic destination. January instead is the coldest month, where temperatures can trop to -5°C. The water temperature of the sea can go from 12°C in the summer months to 3°C during the coldest months.