Indonesia is situated around the equator in southeast Asia. This country is almost entirely tropical. Besides the highest peaks of mountain areas in Papua and Borneo, all major islands have a tropical rainforest climate (Af type according to the Köppen - Geiger climate classification). The smaller islands east of Java and some parts of Java itself have a tropical monsoon climate. That is because these regions have a clearer distinction between a wet and a dry season.
Volcanoes and mountains influence climate and weather conditions
Indonesia's mountainous landscape has a clear influence on its climate. You can even find eternal snow on the highest peak in Indonesia, namely Puncak Jaya (4,884 meters) in Papua. In other areas mainly the location and the season determines where and how much rain falls.
In any case, no lack of rain in Indonesia. The average is 1,500 to 2,500 millimeters rain per year, but some parts are considerably wetter. Especially the mountains in Papua have to deal with more rain on the windward side. On the other islands also mainly the eastern and northeastern slopes get their share of rain.
Indonesia has a rainy season - or monsoon - that officially starts in September or October. The rainy season normally continues untill March. From April onwards, it gets dryer in the whole of Indonesia. The wind then changes from northeast to southeast. During the dry period northern Indonesia still has to deal with some rain during the months June and July. August and September are considerably drier.