Temperatures hover between 85*F to 98°F in Indonesia in December, depending on where you are. The rain is hard and heavy; however, it doesn't occur around the clock. In fact, the storms are usually brief, rarely lasting more than a few hours. Typically what happens is that the day begins sunny and warm. At some point mid-morning or early afternoon, a storm sweeps in suddenly and powerfully. It hammers the region with rain for several hours, and then leaves as fast as it came. Once gone, the beaches, forests, and volcanos return to being dry and beautiful. This makes it possible to still enjoy a great vacation as long as you bring a good rain coat.
Crowds and Costs
The silver lining to the intense rainfall that Indonesia experiences in December is that it keeps the crowds away. The first half of the month, most of the country receives very little tourism. Toward the end of the month, as the Christmas and New Year's holidays approach, the numbers begin increasing and the last half of the month can actually be fairly busy. However, if you're planning a December trip and you want to stay away form the crowds, simply book it in the first part of the month.
Prices follow a nearly identical pattern. The beginning of the month they are cheap. Hotels offer low-season rates and airfare is cheaper too. However, the closer you get to the holidays, the more the prices increase and by Christmas Day, hotels are practically charging high season rates.
Where to Go
Bali is the most ideal place to visit in Indonesia in December. This is because the popular tourist island is less affected by the monsoons and overall it doesn't get quite as much rain (although that by no means indicates that it's completely dry). Another great thing about visiting Bali in December is that generally speaking, the infrastructure is a bit stronger than neighboring islands and you're less likely to experience rainy season hassles like power outages and washed out roads.
Another option is to head to Java where the rain isn't any better but the infrastructure is up to par, mostly due to the capital being there. The eastern part of the island is less rainy so you may enjoy yourself most in places like Surabaya, Lumpur, and other eastern destinations.
Adventurous travelers, who don't mind going off the beaten path a bit, may want to head to the Moluccas Islands (aka Spice Islands). They have a different rainy season than the rest of the country so you won't be hit as hard by storms and precipitation. Just keep in mind that all of these islands fall off the main tourist track and therefore don't have the same degree of amenities. Wifi in particular can be spotty, and there aren't as many restaurants, bars, and nightlife opportunities.
It's best to avoid the islands of Nusa Tenggara, Sumatra, and Lombok this time of year, as they get hit heavily with rain.
Chat with a local specialist who can help organize your trip.
What to Do
In Bali, check out Ubud where you can hike or bike through the lush rice paddies outside of town. Try meditating or taking a class at the Yoga Barn or wander through the famous Monkey Forest (Mandala Suci Wenara Wana) where dozens of Balinese long-tailed monkeys will run up to greet you. Or, drop by the Celuk village outside of town to watch traditional silversmiths in action.
After Ubud, head to Bedugul to see the breathtaking Ulun Danu Temple. The beautiful structure sits on top of the water on Baratan Lake, offering picturesque sunrises (which are actually best seen during the rainy season). If you enjoy a fix of adrenaline, head next to the Bali Treetop Adventure Park or if you prefer tranquility, check out the Bali Botanic Garden.
If you visit Java, swing through the bustling city of Surabaya. It's the second-largest city in Indonesia and as such, offers lots of opportunities for shopping, dining, museums, art, and nightlife. If you're someone who enjoys temples, check out the intriguing Borobudur Temple complex near Yogyakarta or the Candi Prambanan complex by Borobudur. Just don't plan to climb any of the volcanos (such as Mt. Bromo or Mt. Ijen)—they will be too wet this time of year.
Events in December
Christmas: Although Indonesia is primarily a Muslim country (with a fair share of Hindus and Buddhists as well), there are also Christians who celebrate Christmas similarly to Europe and North America. Locals will attend churches and visit cathedrals where you can spot Nativity performances and other familiar rituals. The week between Christmas and New Years can get very crowded so prepare for that if you're going to be visiting during the holidays.
Traveling to Indonesia in December? Check out this great itinerary
Highlights of Bali - 8 Days: If you'd rather have an expert plan your trip than spend a bunch of time doing research, this 8-day guided tour is a great option. It's especially good for a December vacation because all of the activities are in Bali where the rain isn't quite as intense. Among numerous activities, some highlights of the trip include visits to the Uluwatu temple, the Ubud Monkey Forest, the Tanah Lot water temple, and a scenic bike ride through the countryside.