Borneo is the world’s third-largest island, with an area of more than 287,000 square miles covering Brunei Darussalam, Indonesia’s Kalimantan Provinces, and Malaysian Borneo. The island straddles the equator, crossing the Indonesian city of Pontianak (you can walk right over this imaginary line at Pontianak’s Khatulistiwa Park).
Thanks to its equatorial location, Borneo enjoys a humid tropical rainforest climate that remains mostly constant throughout the island, barring outliers like the upper reaches of Gunung Kinabalu, its tallest mountain.
Temperatures throughout Borneo remain constant year-round, averaging between 81 degrees F and 90 degrees F, with a relative humidity of 80 percent.
You’ll only notice a difference between “rainy” and “dry” seasons in terms of the volume of rainfall. The rainy season generally falls between October and March islandwide, bringing an average of 9 inches of rain; Borneo experiences sporadic rainfall even in the supposedly dry season.
Haze Season in Borneo
Palm oil and paper-wood plantations across Borneo are responsible for the seasonal smoky haze that blankets Southeast Asia throughout the second half of each year.
The activity (and the resulting haze) peaks in the dry months between July and October, when small-holders burn down swathes of rainforest to make way for more farming acreage. Prevailing winds blow the haze northwest, blanketing all except the easternmost parts of the island.
The immediate effects of the haze include irritation of your throat, lungs, and eyes. Other side-effects include dizziness, headaches, and fatigue. The haze can also aggravate existing respiratory conditions like bronchitis, asthma, or chronic obstructive pulmonary disease (COPD).
Haze and Your Travel Plans
Travelers to Borneo destinations might find themselves at ground zero during the haze season. The haze may significantly affect your travel plans to and within the island.
Availability of tourist sites are usually affected by the haze; orangutan nature reserves and other open-air destinations in Borneo may be closed.
The haze also affects how you get in and around. Transportation across Borneo borders (by bus or plane) may be rescheduled or called off depending on the intensity of the haze on any given week.
How to Deal With Haze in Borneo
Check beforehand on the severity of the haze in the area you’re visiting. Indonesian Borneo experiences the worst of the haze, with the risk decreasing as you go north to Malaysian Sarawak and Sabah and Brunei Darussalam. Bring face masks in case you’re concerned about the haze in your destination.
Visit the following national and intragovernmental sites for local haze details:
- ASEAN Specialised Meteorological Centre - Air Quality
- Air Pollutant Index of Malaysia
- National Environment Agency (Singapore) - Haze Situation Update
If you find yourself in Borneo during a haze attack, stay indoors; wear a mask if you have to go outdoors. Drink lots of water to help deal with the haze’s effects.
Weather in the Three Countries in Borneo
As the world's third-largest island, the weather can vary depending on which part you're visiting. We've broken this section down by patterns in the three countries that make up the island.
This tiny country occupies a total area of 2,226 square miles (1 percent of Borneo’s landmass) on the northwest coast some four degrees north of the equator. The average temperature in Brunei is 80.8 degrees F (27.1 degrees C).
Two minimum-rain seasons—one from February to April and another from late June to August—brings moderate rains (about 20 inches) and high temperatures ranging from 75.2 to 96.8 degrees F (24 to 36 degrees C). The rain peaks during two wet periods, one from September to January and another from May to mid-June.
The rains during this time peak to 50 inches, with thunderstorms also reaching a crescendo from September to November. Temperatures during the wet season hover between 68 to 82.4 degrees F (20 to 28 degrees C).
The Malaysian states of Sarawak and Sabah make up a fourth of Borneo’s landmass, occupying some 51,026 square miles of the island’s north and northwest. These two states are collectively known as East Malaysia, as opposed to Peninsular Malaysia that occupy the Malay Peninsula between Singapore and Thailand.
Sabah’s equatorial, tropical climate brings near-consistent temperatures all year round: averaging 89.6 degrees F (32 degrees C) in lowland areas like Kota Kinabalu and Sandakan, and 69.8 degrees F (21 degrees C) in highland places like Kundasang and Ranau. The exception is Mount Kinabalu (particularly at elevations above 11,000 feet), with temperatures dropping below freezing in the evenings.
Sarawak’s temperature also depends on the elevation—most lowland areas, like the capital Kuching, enjoy uniform temperatures all year ranging from 73.4 to 89.6 degrees F (23 to 32 degrees C). Highland areas like Kelabit experience cooler temperatures of 60.8 to 77 degrees F (16 to 25 degrees C) in the daytime, sometimes plunging as low as 51.8 degrees F (11 degrees C) in the evenings.
The Northeast Monsoon brings increased rainfall and thunderstorms between November and January, switching to cooler, drier weather from February to April as the Southwest Monsoon takes over. Sarawak’s inland regions are some of the wettest in Malaysia; on average, the state experiences 250 rainy days a year.
The Indonesian provinces of West, Central, South, East, and North Kalimantan occupy the lion’s share of Borneo, some 73 percent of the landmass overall.
Kalimantan weather is consistent with its equatorial location, with coastal temperatures usually hovering between 79 to 81.3 degrees F (26.1 to 27.4 degrees C) year round. Temperatures tend to stay consistently warm and humid; some slight relief is offered by a relatively dry season from June to mid-September, coming between two months of torrential downpours from May to June, and September to November.
At an average annual precipitation of 11.8 inches per year, Kalimantan actually enjoys less rain than neighboring islands like Java and Sulawesi.
Rainy Season in Borneo
The idea of “seasons” in Borneo feels somewhat meaningless, given the island's almost uniform heat and humidity. The rainfall experiences highs and lows throughout the year, with peak rains falling between October and March; the actual rainfall levels vary greatly depending on the location and the elevation.
What to pack: When visiting Borneo during the wet season, prepare for constant rain. You’ll want to bring an umbrella and waterproof bags or backpacks; don’t wear a poncho or a raincoat, the humidity will make the inside feel swampy in a few minutes.
Pack waterproof flashlights, plastic bags to store your electronics in, and DEET mosquito repellent. Be prepared to change your plans on the dot, as the rains may suddenly upset your preparations (e.g. flooded roads, closed destinations).
Dry Season in Borneo
Borneo experiences constant rainfall throughout the year, so the local “dry” season consist of months where the rainfall only happens in brief afternoon showers, instead of the rainy season’s unrelenting torrents.
The dry season varies from place to place, coinciding with the local peak tourist season. Generally speaking (local variations notwithstanding) the islandwide dry season takes place from March to October. These are excellent months in which to schedule a climb up Mount Kinabalu in Sabah, or visit the orangutans in the Borneo jungles—just make sure the haze doesn’t get in the way of your visit.
What to pack: Take both rain and sun into account—rain showers can fall even in the sunniest months of the year in Borneo. Take a swimsuit for the beaches, and bring high-SPF sunblock too; the equatorial sun can be quite unforgiving. If you’re planning to hike up a mountain or through one of the many national parks on the island, pack the right trekking shoes, breathable clothes, and a hat to ward off the sun.
Wonderful Indonesia. "The Equatorial Monument, Landmark Right on the Equator Line."
HealthHub. "Impact of Haze on health."
Sabah Tourism. "Essential Information Before You Travel."
Official Portal of the Sarawak Government. "The Geography of Sarawak."