Typical annual rainfall varies between 4,000 - 6,000 mm/year, very high even for West Java!
The wet season occurs from October to April, with precipitation around 400-600 mm/month. Even in the so-called "dry season", June to September, rainfall is usually in excess of 200 mm/month.

During the day warm air rises over the land and warm, saturated air from over the ocean moves in to take its place. When this humid air reaches the mountains it cools; water condenses into clouds and a deluge of rain follows (orthographic precipitation). Rainfall here is strongly influenced by seasonal changes in wind direction.