Climate Introduction

Climate Introduction

The climate of Indonesia is almost entirely tropical. The uniformly warm waters that make up 81 % of Indonesia’s area ensure that temperatures on land remain fairly constant, with the coastal plains averaging 28°C, the inland and mountain areas averaging 26 °C, and the higher mountain regions, 23 °C. Temperature varies little from season to season, and Indonesia experiences relatively little change in the length of daylight hours from one season to the next; the difference between the longest day and the shortest day of the year is only forty-eight minutes. This allows crops to be grown all year round. The main variable of Indonesia’s climate is not temperature or air pressure, but rainfall. The area’s relative humidity ranges between 70 and 90%. Winds are moderate and generally predictable, with monsoons usually blowing in from the south and east in June through September and from the northwest in December through March. Typhoons and large scale storms pose little hazard to mariners in Indonesia waters; the major danger comes from swift currents in channels, such as the Lombok and Sape straits.

Monsoons The extreme variations in rainfall are linked with the monsoons. Generally speaking, there is a dry season (June to October), influenced by the Australian continental air masses, and a rainy season (November to March) that is the result of- Asia and Pacific Ocean air masses. Local wind patterns, however, can greatly modify these general wind patterns, especially in the islands of central Maluku—Seram, Ambon, and Buru. This oscillating annual pattern of wind and rain is related to Indonesia’s geographical location as an isthmus between two large continents. In September and May, high pressure over the Gobi desert moves winds from that continent toward the northwest. As the winds reach the equator, the Earth’s rotation causes them to veer off their original course in a northeasterly direction toward the Southeast Asian mainland. During January and February, a corresponding low pressure system over Asia causes the pattern to reverse. The result is a monsoon which is augmented by humid breezes from the Indian Ocean, producing significant amounts of rain throughout many parts of the archipelago.

Prevailing winds Prevailing wind patterns interact with local topographic conditions to produce significant variations in rainfall throughout the archipelago. In general, western and northern parts of Indonesia experience the most precipitation, since the north- and westward-moving monsoon clouds are heavy with moisture by the time they reach these more distant regions. Western Sumatra, Java, Bali, the interiors of Kalimantan, Sulawesi, and Papua are the most predictably damp regions of Indonesia, with rainfall measuring more than 2,000 millimeters (78.7 in) per year. In part, this moisture originates on high mountain peaks that trap damp air. The city of Bogor, near Jakarta, lays claim to having the world’s highest number of thunderstorm days per year—322. On the other hand, the islands closest to Australia—including Nusa Tenggara and the eastern tip of Java—tend to be dry, with some areas experiencing less than 1,000 millimeters (39.4 in) per year. To complicate the situation, some of the islands of the southern Malukus experience highly unpredictable rainfall patterns, depending on local wind currents. Temperature Although air temperature changes little from season to season or from one region to the next, cooler temperatures prevail at higher elevations. In general, temperatures drop approximately 1° per 90-meter increase in elevation from sea level with some high-altitude interior mountain regions experiencing night frosts. The highest mountain ranges in Papua are permanently capped with snow.

Indonesia Climate Map

The Weather in the Dry and Wet Season and the time between

When to go Straddling the equator, Indonesia tends to have a fairly even climate year-round. Rather than four seasons, Indonesia has two – wet and dry – and there are no extremes of winter and summer. In most parts of Indonesia, the wet season falls between October and April (low season), and the dry season between May and September (high season). Rain tends to come in sudden tropical downpours, but it can also rain nonstop for days. In some parts of the country, such as Kalimantan, the difference between the seasons is slight – the dry season just seems to be slightly hotter and slightly drier than the wet season. In other areas, such as Nusa Tenggara, the differences are very pronounced, with droughts in the dry season and floods in the wet. Though travel in the wet season is not usually a major problem in most parts of Indonesia, mud-clogged back roads can be a deterrent. The best time to visit is in the dry season. The ‘wet’ starts to descend in October and varies in intensity across the archipelago. The December to February rains can make travel prohibitive in Nusa Tenggara, when rough seas either cancel (or sink) ferries, and roads on Flores are washed out. Parts of Papua are also inaccessible. The rains shift in Sumatra, peaking from October to January in the north, and from January to February in the south. But seasonal change makes little difference in Bali, and in Kalimantan higher water levels from December to February improve access to rivers and small tributaries. In most cases, experiencing an Indonesian festival is reason enough to head to a destination. Some are so significant, however, that they can generate difficult conditions for travellers. Tana Toraja’s funeral season boosts Rantepao’s population, and hotel prices, substantially during July and August. In Java it’s a good idea to avoid the final days of Idul Fitri, when public transport is mayhem and some businesses close. A tragic drop in tourist hordes means that Indonesia’s ‘high season’ no longer presents the same kind of bother it once did. The December–January Christmas holiday period and the school holidays still brings a wave of migratory Australians, and Europeans head to Bali, Java, Sumatra and Sulawesi in July and August. But climatic impediments aside, pretty much any time is a good time to head to Indonesia at the moment. The main Indonesian holiday periods are the end of Ramadan, when domestic tourists fill resorts and prices escalate; Christmas; and mid-June to mid-July, when graduating high-school students take off by the busload to various tourist attractions, mainly in Java and Bali.