On Vanuatu, the seasons are the opposite of the European ones. The islands have a tropical climate, subtropical in the south, with high humidity.
During the dry season, which lasts from May to October, it rains very rarely and temperatures are pleasant (average 22-24°C). The rainy season from December to April is usually hot. So the average temperature in Port Vila at this time is about 28°C. Also the humidity is much higher than during the dry season. The islands south of Port Vila are generally cooler and have less rainfall.
Vanuatu is best visited in summer.