Indonesia straddles the Equator between the Indian Ocean and the Pacific Ocean. While it has land borders with Malaysia to the north as well as East Timor andPapua New Guinea to the east, it also neighbors Australia to the south, and Palau, the Philippines, Vietnam,Singapore, and Thailand to the north,India to the northwest.
Upon arrival and disembarking from the plane, you'll immediately notice the sudden rush of warm, wet air. Indonesia is a warm place. It has no spring, summer, fall, or winter, just two seasons: rainy and dry, both of which are relative (it still rains during the dry season, it just rains less). 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.
In the highlands temperatures will naturally be cooler, and there are even snow-covered peaks in Papua, whose mountains can soar above 5000 meters. Bring along a jacket if planning to visit eg. Mount Bromo on Java or Tana Toraja in Sulawesi.