The dry season, roughly May to October, is the best time to visit. Rain is still possible, especially in the Highlands, but the trails are drier, the roads are more passable, and visibility for diving is generally better.
August and September are the peak months for cultural festivals. The Mount Hagen Sing-Sing in August draws over 50 tribal groups to the Western Highlands for two days of dancing, face paint, and elaborate headdresses. In September, the Goroka Show — held over the Independence Day weekend — is the largest cultural gathering in the country, attracting around 100 cultural groups and tens of thousands of visitors to the Eastern Highlands. Book accommodation months in advance for either event.
The wet season (November to April) brings heavy rain, particularly to the north coast and islands. The Kokoda Track becomes very muddy and difficult. Flights in the Highlands are more frequently delayed. That said, the country is less busy and some diving destinations — particularly Tufi and Milne Bay — can be excellent even in the wet season, as rainfall here is year-round anyway.
The Highlands have a cooler climate than the coast due to altitude. Nights above 2,000 metres can be cold, and you should pack warm layers even if you are visiting in the dry season. The coasts are hot and humid throughout the year.