Climate of Indonesia

The climate of Indonesia is almost entirely tropical, which means it stays warm and wet most of the time. Because so much of Indonesia is covered by warm waters, temperatures on land do not change much. Coastal areas are usually around 28 °C (82 °F), while mountain areas are cooler, averaging about 26 °C (79 °F). In the highest mountains, temperatures can drop to around 23 °C (73 °F). The weather stays fairly steady throughout the year, with only a small difference in daylight between the longest and shortest day of the year—just forty-eight minutes.

What changes most in Indonesia’s climate is the amount of rain. The air is very humid, between 70 and 90% moist, and the winds follow a pattern, bringing rain from different directions during different months. From June to September, winds come from the south and east, and from December to March, they come from the northwest. Big storms and typhoons are rare, but fast currents in narrow channels like the Lombok and Sape straits can be dangerous.

Indonesia has many different climate zones. Most of the country has a tropical rainforest climate, which gets the most rain, followed by tropical monsoon and tropical savanna climates, which are drier. In some high mountains, you can find oceanic climates and subtropical highland climates. Even higher up, in places like the Papuan highlands, the climate can be as cool as a tundra climate or subpolar oceanic.

Monsoons

The changing rain patterns in Indonesia are connected to what are called the Australian-Indonesian monsoons. There are two main seasons: a dry season from April to September and a rainy season from October to March. These seasons are influenced by air moving from Australia and from Asia and the Pacific Ocean.

Local winds can change these patterns, especially in some central islands. The shifting winds and rain happen because Indonesia lies between two large land areas. In some months, winds from far away change direction due to Earth's rotation, bringing rain when they meet humid breezes from the Indian Ocean. This creates the rainy season in many parts of the Malay Archipelago. See also monsoon trough.

Prevailing winds

Wind patterns and local geography cause different amounts of rain across Indonesia. The western and northern areas, like Western Sumatra, Java, Bali, and parts of Kalimantan, Sulawesi, and Papua, get a lot of rain—over 2,000 millimeters each year. Some of this rain comes from moist air trapped by tall mountains.

Areas closer to Australia, such as Nusa Tenggara and the eastern part of Java, are drier, with some places getting less than 1,000 millimeters of rain yearly. In the southern Malukus, rain can be hard to predict because of local winds.

Temperature

See also: Climate

The air temperature in Indonesia stays about the same all year and doesn’t change much from one place to another. However, it gets cooler as you go up higher. For every 90 meters you climb, the temperature drops by about 1 °C. In some very high mountains, it can even get cold enough at night for frost, and the tallest mountains in Papua are always covered in snow.