Climate

Climate and Weather Characteristics

The archipelago of Indonesia belongs to the Austral-Asiatic tropical zone. Climatic and weather condition of the archipelago is characterized by an equatorial double rainy season. Its variation is caused by the equatorial circulation and the meredional circulation.

Displacement of the meredional circulation is closely related to the north-south relative movement of the sun and its position at a certain period with regard to the earth and the continents of Asia and Australia. These factors contribute to the displacement and intensity of the Inter-Tropical Convergence Zone being an equatorial trough of low pressure. This characterizes the weather of Indonesia; while the prevalence of the west monsoon and the east monsoon (wet and dry seasons) are characterizing the climate of Indonesia.

Monsoon and Rainfall

When relative position of the sun is on the north hemisphere from mid-March to mid-September, relatively dry winds blow over the archipelago from the southeast - the arid continent of Australia; and east monsoon characterizing dry season takes place on a large part of the archipelago. The dry season is generally prevailing from May to September.

On the other hand, when relative position of the sun is on the south hemisphere from mid-September to mid-March, wet winds blow over the archipelago from the northeast - the humid continent of Asia; then west monsoon characterizing wet season takes place in most parts of the archipelago. The wet season is generally prevailing from December to March.

However, these patterns do not always rigidly take place since a large part of the archipelago is covered by sea and diurnal differences are not significant, which makes precipitation be possible anytime. Sunshine is abundant, but rainfall - either heavy or light storms - can also drop in the dry season period. Rain even falls nearly all the year round on the islands where equator passes through, and this had resulted in dense natural tropical rainforest on the islands of Sumatera, Kalimantan, Sulawesi, and also in Irian Jaya.

Humidity and Temperature

Being within the humid equatorial zone, Indonesia has a high degree of air relative humidity with an average minimum of 60%. A minimum of 20% was observed in Jakarta in 1972. On the average, the mean annual air relative humidity ranges around 80% - 90%.

The annual mean air temperature in Indonesia is around 33^oC. As for the higher mountainous region, the monthly mean air temperature ranges approximately 25^oC - 28^oC. The mean maximum temperature can reach 33^oC, whereas the mean minimum air temperature is 21^oC.

Wind and Storm

The average wind velocity is generally less than 15 knots per hour. Strong wind may be blowing occasionally in any parts of Indonesia that is usually closely related to tropical storms. Wind velocities of 45 knots per hour were reported from Rembiga in January 1976, from Surabaya in January 1973, and from Ujungpandang in January 1974.

Nevertheless, the tropical storms are rare in Indonesia as it is anticipated that these would not develop in land areas within the latitude of less than 70^o. Despite this anticipation, however, reports of tropical storms were recorded at Banda area in April 1778, at the islands of Rote and Timor in April 1843, and the giant ones at Timor in 1918 and on the island of Flores in 1973 and 1993.

Today's Weather Forecasts

Weather forecasts for some big cities in Indonesia are provided. Thanks to the Weathernews Inc., the daily and weekly weather forecast data are automatically updated. You may also view the satellite imagery presenting current weather conditions of Central Asia and Pacific Rim, where Indonesian Archipelago lies.