The weather is great in Indonesia in September. In Bali and Sumatra, for instance, the temperatures are warm and sunny but not sweltering. Bali is cooler, averaging about 82°F to 86°F while Sumatra creeps up to around 86°F to 93°F. Java is considerably hotter than both with daytime highs around 91°F to 97°F throughout the month. In the evenings, most of the islands cool off to about 71°F to 77°F—a refreshing change but still pretty warm.
Rain-wise, there's essentially no precipitation except for a few isolated places such as the northern part of Sulawesi and around the Raja Ampat islands.
Crowds and Costs
The best part of September is that the crowds begin tapering off ever so slightly. It's still high season—make no mistake—but compared to the previous months they are better and the numbers of people at the beaches and temples start to wane. You'll still contend with big crowds, especially in Bali and the more popular islands, but generally speaking it won't be as intense.
Unfortunately, the costs don't follow the same pattern. September is still very much considered peak season and hotels will be charging maximum rates. Airfare will be expensive, too. If you're considering a trip during this time, book everything in advance to get the best rates.
Where to Go
The beautiful thing about visiting Indonesia in September is that it's virtually an open map in terms of which islands to go to. With the exception of some lesser-visited destinations like Northern Sulawesi or the Raja Ampat islands, they're all great this time of year.
Bali makes a fantastic starting point. The southern part of the island is full of beaches that offer warm, salty water and gentle ocean breezes. The weather is great and the resorts won't be quite as packed as earlier in the summer. It's also a good time to go to Ubud and other more central parts of the island where you can explore rice paddies or take a yoga retreat.
Or, if that islands isn't of interest, head to Java, another great option that also has stunning beaches, along with spectacular volcanos and numerous trekking opportunities. It's the perfect time of year to hike Mt. Bromo or Mt. Ijen when the ground is dry and you don't have to worry about rain. Java also has tons of picturesque temple complexes that make perfect September destinations.
Sumatra is another good September choice. Its location right on the equator divides the north and south parts of the island into different weather patterns. The latter gets washed out with rain during the off season but in September, places like Palembang (the “Venice of the East”) and other southern destinations are idyllic.
Other tourist-friendly islands nearby include Nusa Tenggara, Sumba, and Flores.
What to Do
Head to Bali and visit Kuta beach, a laidback surf town with stunning white sands beaches and crystal blue water. You can surf, snorkel, sunbathe, or sea kayak. There are even opportunities to ride jetpacks on the water in the nearby Tanjung Benoa. In addition to beach activities and water sports, Kuta is famous for its wild nightlife. Check out places like Paddy's Pub or head to the Hard Rock Café Bali for music and entertainment.
In Java, book a tour to climb to the top of one of its famous volcanos such as Mt. Bromo or Mt. Ijen. Or, if you're not into trekking, check out the sacred Candi Prambanan temple complex near Borobudur or the Borobudur Temple by Yogyakarta. If you're hankering for some city life, explore Surabaya which offers great food, shopping, and nightlife.
If Sumatra is on your list, September is a wonderful time to soak up some of that island's rich culture. In Medan, for example, visit the Mesjid Raya Al Mashun mosque or stop by the Istana Maimun, a stunningly built royal palace that was once home to the Sultanate of Deli. Drop by the Tjong A Fie Mansion or stroll through Merdeka Walk. Down south, check out Palembang which is home to sites like the Kuto Besak Fort palace and the Great Mosque of Palembang.
Events in September
Hari Olahraga Nasional (National Sports Day): This yearly holiday typically falls the first week of September. During the state event, Indonesians host traditional sporting tournaments that involve a lot of food and celebration.
Traveling to Indonesia in September? Check out this great itinerary
Temples and Trekking from East Java to Bali: If you're planning a trip to Indonesia in September but you don't want to hassle with all of the planning, this 14-day guided trip is the perfect solution. It takes you to all of the best places in both Bali and Java including three different volcanos and a handful of scenic beaches. Highlights include snorkeling near Menjangan Island and visiting the sacred temples at Candi Prambanan and Borobudur.