Jakarta is hot and humid year-round, with daytime temperatures hovering around 30 to 33 degrees and uncomfortable humidity that rarely lets up. The dry season runs roughly May to October and is the best time to visit -- still hot, but the rain mostly stays away and traffic flows a little better. The wet season, November to April, brings heavy afternoon downpours that flood low-lying parts of the city and snarl traffic for hours.
Avoid travelling around Eid al-Fitr (Lebaran), when much of the city empties out as residents head back to their home villages -- shops shut, restaurants close, and the normally choked roads briefly go quiet. The Jakarta Anniversary celebrations in late June bring street parades and concerts. The annual Jakarta Fair (Pekan Raya Jakarta), running from mid-June to mid-July, is a sprawling trade and entertainment event drawing huge local crowds.