Nias has a tropical rainforest climate with no true dry season — average temperatures hover around 26°C year-round, and rain is possible in any month. The wettest period runs from October through March, when swells are also at their best for the surf breaks in the south. The driest and calmest months are generally May through August, which makes travel more comfortable and ferry crossings less rough.
The Ya'ahowu Festival is the main cultural event on the island's calendar, usually held in October or November in Gunungsitoli. Traditional Nias music, dance (including the dramatic war dance Fatele), and craft are on display; stone jumping (Fahombo) demonstrations are often part of the programme. Check the local calendar when planning — the exact dates move year to year. If you want to see traditional Nias culture at its most vivid and concentrated, timing your visit around the festival is worth the effort.