Iwakuni: 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: August, has temperatures that can reach 29°C, it's the hottest month at this touristic destination. January instead is the coldest month, where temperatures can trop to 7°C. The water temperature of the sea can go from 26°C in the summer months to 12°C during the coldest months.