Depending on the area one visits, the temperature, humidity and UV exposure can vary greatly.
Similar to its neighbour (Australia) to the south, Papua New Guinea has a "dry season" and a "wet season" although unlike its neighbours, this isn't a guide to the weather one may experience.
Generally speaking the dry season starts around May/June and continues through to September/October although a torrential downpour is NOT unheard of at all times of the year.
It is drier and cooler up in the mountain regions and along the Kokoda Track, it's even dropped to -2 around Templetons Crossing on some trips.
The coast is wetter (humid) and warmer, which makes it very hot and sticky. The suns heat is very strong and burning is a major risk especially if one is taking anti malarial medications.
The following chart shows an average temperature taken over a period of several years from Port Moresby
