Indonesia’s Climate can be classified as AF climate by the Koeppen-Geiger clas- sification: a hot, humid tropical climate with all months above 18°C. The main variable of Indonesia’s climate is not temperature or air pressure, but rainfall. Split by the equator, Indonesia has an almost entirely tropical climate, with the coastal plains averaging 28°C, the inland and mountain areas averaging 26°C, and the higher mountain regions, 23°C. The area’s relative hu- midity is quite high, and ranges between 70 and 90 per- cent. The extreme variations in rainfall are linked with the monsoons. There is a dry season (June to Septem- ber), and a rainy season (December to March). Western and northern parts of Indonesia experience the most precipitation, since the north- and westward-moving monsoon clouds are heavy with moisture by the time they reach these more distant regions. Western Suma- tra, Java, Bali, the interiors of Kalimantan, Sulawesi, and Irian Jaya are the most predictably damp regions of Indo- nesia, with rainfall measuring more than 2,000 millime- ters per year. Typhoons can hit the Islands of Indonesia between September and December and can cause rain- storms and heavy winds. However, not every Typhoon that hits Indonesia is a strong one, and in some years only a few Typhoons occur during the tropical storm season.