In December, some rain can be expected in Bali and Lombok and much of Indonesia once every 2 or 3 days. This is the height of the rainy season in Bali and Lombok. Nevertheless, temperatures are still high and clear days with sunny skies can still be expected for much of the time.
This is the wettest time of year in Northern Sumatra and travel can be made difficult because of heavy rain.
In Nusa Tenggara rain can be expected almost everywhere in December.
Southern Sulawesi is under the influence of the Southwest monsoon and afternoon downpours can be expected in December. In the north, around Manado, the opposite monsoon system also brings rain to the Northern Sulawesi, although rainfall is fairly moderate.