The climate of Indonesia is almost entirely tropical. The uniformly warm waters that make up 81% of Indonesia’s area ensure that temperatures on land remain fairly constant, with the coastal plains averaging 28 °C, the inland and mountain areas averaging 26 °C, and the higher mountain regions, 23 °C. Temperature varies little from season to season, and Indonesia experiences relatively little change in the length of daylight hours from one season to the next.
The main variable of Indonesia’s climate is not temperature or air pressure, but rainfall. The area’s relative humidity ranges between 70 and 90%. Although air temperature changes little from season to season or from one region to the next, cooler temperatures prevail at higher elevations. In general, temperatures drop approximately 1°C per 90-meter increase in elevation from sea level with some high-altitude interior mountain regions experiencing night frosts.
Being a tropical country, Indonesia does not have spring, summer, autumn, or winter, instead just the two seasons of Rainy and Dry, both of which are relative. While there is significant regional variation, in most of the country (including Java and Bali) the dry season is April to October, while the wet season is November to March. However, global warming has made the seasons less predictable.