Sumatra in December: rain, jungle and the quiet season

Sumatra is the sixth-largest island in the world, and its weather is not one thing. The west coast, including Bukit Lawang and the Barisan mountains, takes the full force of the northwest monsoon from October to March. The east coast and the Riau islands are drier, and the far south around Lampung has its own pattern.

December is therefore a month of choices. If you want orangutans and jungle, you accept rain and leeches. If you want Lake Toba, you accept cloud on the crater rim and a lake that is grey rather than blue. What you get in return is space: the guesthouses in Bukit Lawang are half empty, the trails are quiet and the prices are low.

What the wet season means here

Rain on the west coast is frequent and heavy, often in the afternoon and evening, with the occasional grey day that never clears. Humidity stays high, the rivers rise quickly, and the jungle trails turn to mud. Leeches are active, and the mosquitoes that carry dengue breed in the standing water along the trails.

Temperatures remain warm, from 23°C in the highlands at night to 31°C on the coast. Bukit Lawang sits at about 100 metres and is humid; Berastagi and the Lake Toba rim are cooler and need a light jacket in the evening. The rain is not usually cold, but it arrives hard and fast.

• Rain most afternoons on the west coast
• High humidity, muddy trails
• Leeches and mosquitoes active
• Highlands cooler at night

Orangutans at Bukit Lawang

Bukit Lawang is the main gateway to the Gunung Leuser National Park and its Sumatran orangutans. The semi-wild population around the rehabilitation centre is used to people, and the twice-daily feeding sessions at the platform are the easiest way to see them. The wild population requires a trek, usually a half-day or full-day walk with a licensed guide.

In December the treks are muddier and slower, and the river crossing to the trailhead can be too high to wade. Guides adapt, but a full-day trek may become a half-day. Wear shoes with grip, bring a rain jacket and accept that the orangutans, not the schedule, decide what happens.

Lake Toba and Samosir

Lake Toba is a volcanic caldera 100 kilometres long and up to 500 metres deep, with Samosir island in the middle. The Batak villages around the shore have traditional houses with buffalo-horn roofs, and the pace is slow even by Sumatran standards. In December the lake is often covered in cloud by mid-morning, and the views from the rim are hit and miss.

The ferry to Samosir runs from Parapat and takes about 45 minutes to an hour, or you can drive around the lake. Tuk-tuk is the main village on the island, with guesthouses, restaurants and scooters for rent. Rain makes the lake roads slippery, and the winding descent to the shore is not the place to test your braking.

Medan, Berastagi and the north

Medan is the gateway, served by Kualanamu airport about 40 kilometres from the city. It is a hot, chaotic, interesting city with colonial buildings, a large Chinese community and some of the best food in Sumatra. Most travellers pass through in a day, which is a mistake if you like markets and street food.

Berastagi sits in the Karo highlands at 1,300 metres, between Medan and Lake Toba, with volcanoes, fruit markets and cooler air. The December rain makes the trails to Sibayak and Sinabung slippery, and Sinabung is an active volcano with an exclusion zone that is enforced. Check the current status before planning a climb.

• Kualanamu airport, 40km from Medan
• Berastagi at 1,300m, cooler
• Sinabung exclusion zone enforced
• Check volcano status locally

Getting around in the rain

Roads on the west coast are slow and winding, and the wet season brings landslides and flooded sections. The Medan to Bukit Lawang drive takes three to four hours in good conditions and longer after rain. The Medan to Parapat road to Lake Toba takes four to five hours, and the bus is cheaper but slower than a private car.

Domestic flights connect Medan with Jakarta, Batam, Padang and Banda Aceh, and the smaller airports of Silangit and Aek Godang serve Lake Toba and the surrounding area. Flights are often delayed in December, so do not book a tight connection to an international departure.

Shared cars and tourist buses are the other option on the main routes, and they are cheaper than a private transfer. They also stop more often and leave when full, which in the wet season can mean a long wait at a roadside stall.

Health and safety in the jungle

Bring repellent with DEET, long sleeves and trousers for trekking, leech socks if you have them, and a good rain jacket. Boots are better than trainers on the muddy trails, and a dry bag protects your camera. Do not touch the orangutans, do not feed them, and keep a distance of several metres even when they approach.

There are clinics in Bukit Lawang and Parapat, and a better hospital in Medan. Rabies is present in Sumatra, and any animal bite needs immediate treatment. Travel insurance with evacuation cover is worth having, because a serious injury in the jungle means a road transfer to Medan before anything else.

• DEET repellent and long sleeves
• Leech socks for wet trails
• Keep distance from orangutans
• Rabies treatment in Medan

Is December worth it

If you want orangutans without crowds and you do not mind rain, yes. The jungle is dramatic in the wet season, the rivers are full and the guesthouses are cheap. If you want blue lake views and dry trails, come in June or July instead, when Sumatra's west coast is at its driest.

Questions people actually ask

Is December a good time to visit Sumatra?

It is the wet season on the west coast, with rain most days. It is quiet and cheap, and the jungle is at its most dramatic, but trails are muddy and lake views are often clouded.

Can I see orangutans in December?

Yes. The semi-wild orangutans at Bukit Lawang are seen year-round, and wild ones on guided treks. Rain makes the trails slower, so allow more time.

How do I get to Lake Toba?

Fly to Medan, then drive four to five hours to Parapat and take the ferry to Samosir, or fly to Silangit airport and continue by road.

What should I pack for Sumatra in December?

A rain jacket, quick-dry clothes, grippy shoes or boots, leech socks, DEET repellent and a dry bag. A light jacket helps in the highlands at night.