Taking into account the local weather in Mount Hagen is an important factor for planning your visit, especially if you plan to spend your trip poolside. The hottest months are usually November and May with an average temp of 62°F, while the coldest months are August and July with an average of 62°F. The rainiest months in Mount Hagen are March, January, February, and December, with each month seeing an average of 29 inches of rainfall.