Because of Indonesia's location near the equator and its island geography, the climate along coastal areas is hot and humid year-round. The average daily temperature range of Jakarta is 21° to 33°C (69° to 92°F) and varies little from winter to summer. Temperatures in upland areas tend to be cooler.

Indonesia has two monsoon seasons: a wet season from November to March and a dry season from June to October. Between monsoons, the weather is more moderate. The northern parts of the country have only slight differences in precipitation during the wet and dry seasons. Average rainfall in the lowlands varies from 1,780 to 3,175 mm (70 to 125 in) per year, and in some mountain regions rainfall reaches 6,100 mm (240 in) per year. The regions with the highest rainfall include the mountainous western coast of Sumatra and the upland areas of western Java, Kalimantan, Sulawesi, and Papua. Humidity is generally high, averaging about 80 percent yearly.

The driest parts of the country, with annual rainfall under 1,000 mm (40 in), are along the coast of the Lesser Sunda Islands and the easternmost end of Java. The erratic seasonal distribution of rain in these areas makes farming difficult.

Indonesia lies beyond the typhoon zone of the western Pacific and the especially powerful storms of the South China Sea. Occasionally a typhoon sweeps through the eastern seas but rarely reaches the Java Sea.