Generally speaking, the best time to visit Sumatra is from May to August, during the peak of dry season. Which part of Sumatra you’re visiting matters, though. Indonesia’s largest island is, well, large, and rainfall varies between North, West, and South Sumatra. But one thing is for certain: You’ll have warm weather while exploring the fascinating Indigenous cultures and rainforests.
No matter where you decide to travel to Sumatra, use this guide for choosing the best time to enjoy your adventure!
Weather in Sumatra
The equator slices neatly through the middle of West Sumatra, keeping heat and humidity high. Expect daytime temperatures ranging from 80 to 90 degrees F, and humidity hovers between 80 and 90 percent. Evenings are more comfortable, with temperatures dipping into the 70s. Unless you’re gaining elevation while climbing one of the many volcanoes or getting drenched while motorbiking around Lake Toba, you probably won’t be chilly in Sumatra.
Heavy rains occur throughout the year to keep the rainforests green and thriving. Downpours are typically shorter and less frequent in the drier summer months between May and September, but you should be ready for them at any time. Read more about monsoon season below.
Big Holidays and Festivals
Chinese New Year causes a surge in visitors to Lake Toba and Samosir Island. Christmas, too, triggers an increase in domestic travel. But even with the holiday spikes in visitors, crowds are nowhere near the volume seen in other popular destinations around Indonesia. Unfortunately, you’ll still pay more for less (and possibly endure rainy weather) if traveling to Lake Toba during Chinese New Year.
Indonesian Independence Day (Hari Merdeka) is on August 17, and causes some short-term transportation delays as colorful processions fill the streets and businesses close. But getting to see the various ethnic groups in full regalia or catch a panjat pinang competition is worth the minor inconvenience.
Best Time for Diving
Sumatra doesn’t appeal to divers as much as Papua and Borneo, but Pulau Weh, located in the Andaman Sea at the top of North Sumatra, offers warm water and excellent dive sites. The best months for diving in Sumatra tend to be June, July, and August when visibility is best and the sea is calmest. Pulau Weh doesn’t really have a predictable whale shark season, but the few seen there are most often spotted in December or January.
The Riau Archipelago between Sumatra and Singapore is another top place to dive in Sumatra. The best months for diving there are from April to September, when winds are calmest.
Best Time for Surfing
June and July are the best time for surfing in Krui, one of Sumatra’s top surfing spots. As expected, these months are also the busiest and a great time to meet fellow surfers.
If you’re lucky enough to be surfing West Sumatra’s Mentawai Islands, the waves run all year long. The surf is milder in winter (December to March), at the end of which size and ferocity of waves increase into the summer. Swells get serious from May to September, reaching their most intimidating heights in July and August. Surfing season in Sumatra conveniently coincides with high season in Bali.
Sumatra's Dry Season
Although dry season (May to August) is overall the best time to visit Sumatra, it’s also the busiest season, with prices for guesthouses at their highest (although they’ll still feel like a bargain when compared to prices in Bali). That said, Sumatra doesn’t really suffer from high-season spikes of tourism like others islands. Even during the peak of dry season, you won’t have to worry much about finding hotel vacancies or domestic flights. Your top-pick guesthouse may be booked up in a popular destination such as Lake Toba, but there will be plenty of rooms available elsewhere.
Don’t let the label “dry season” lull you into thinking your outdoor adventure plans won’t be affected by weather. Downpours during dry season don’t typically last long, but their torrential strength will surprise you! Flash flooding and mudslides can be a threat when hiking around waterfalls and gullies. Always have a quick plan for waterproofing important things whether you’re trekking, driving a scooter, or watching a pacu jawi meet (traditional cow racing).
In any given year, the monsoon season’s start and finish are unpredictable. The island's long, northwest-southeast orientation causes monsoon season to begin around November in South Sumatra and around October in North Sumatra. As rainy season approaches, the intervals between cloudbursts become shorter and shorter. Sizzling periods of hot sun between showers keep humidity levels soaring.
Like elsewhere in Southeast Asia, you can visit Sumatra during the monsoon season for low-season discounts; however, you may not be able to enjoy all the activities you had in mind, as many of the best things to do in Sumatra are outdoors and affected by weather. For example, some of the trails, particularly around volcanoes, become muddy washouts during monsoon season. Instead of meeting fellow hikers out on the trails, you’ll get to meet far more leeches and mosquitoes than preferred. The increase in mosquitoes, consequently, increases the chance of contracting mosquito-borne illnesses such as dengue.
Similarly, Sumatra’s jungle rivers may become raging during monsoon season, causing silt and runoff to affect visibility for diving. If you plan to dive during monsoon season, choose sites as far from shore as possible.
Sadly, Sumatra is one of the most deforested places on earth due to unsustainable palm oil practices. The sprawling plantations clear undergrowth by setting illegal fires that burn for months. The amount of greenhouse gas released annually has detrimental global impact. During Sumatra’s burning season, thick haze drifts into Singapore and Malaysia. Airborne particulate matter reaches dangerously unhealthy levels, prompting stay-inside orders in many cities. Despite efforts from governments to stop the fires, burning season is an annual event, with some years worse than others.
Although there is no “official” start to burning season in Sumatra, haze really begins to accumulate in July and September. Air quality is affected in some destinations until the rainy season arrives to clean things up. Travelers with respiratory ailments should check air quality before traveling to Sumatra.
Different Provinces in Sumatra
With Sumatra being so large, when you should plan on traveling depends on which province you're planning to visit. Read on for our guide to the best time to visit Sumatra, broken down by province.
The best month for visiting North Sumatra is May, when days are clear but visitors are fewer. Although the rest of Sumatra offers plenty of adventure, travelers are drawn to the accessibility of Lake Toba, Bukit Lawang, and Samosir Island—the latter of which often feels noticeably cooler than the rest of Sumatra thanks to fresh breezes blowing steadily across the big caldera lake.
Due to the surge in prices, people, and noise, Chinese New Year is not the best time to visit Lake Toba. Furthermore, strong winds between November and February can turn the one-hour boat from Parapat to Samosir Island into a choppy ride; be prepared if you’re prone to seasickness!
Padang, the capital of West Sumatra, is one of the rainiest cities in Indonesia. The many rivers around Padang overflow their banks and regularly cause flooding during winter's rainy season. July is an ideal month for visiting West Sumatra, although February can also be surprisingly dry for winter.
Meanwhile, October, November, and December are especially rainy in West Sumatra. With an average of 164 inches of rain, West Sumatra receives over five times the average annual rainfall of the contiguous United States!
The best months for visiting South Sumatra are during dry season, from June to September. High temperatures increase through September and October, until rainy season arrives in November. December is often the wettest month.
Palembang, the capital of South Sumatra, averages over 103 inches of rain a year. Even with all the rain, Palembang is subject to poor air quality during Sumatra’s burning season. Unhealthy haze caused by illegal fires is often at its worst in July and September.