Pontianak is on the equator and has no dry season as such — it rains throughout the year, typically in short heavy tropical downpours rather than sustained rain. The wettest months are October to February. The driest and sunniest period is generally June to September, which is the best time to visit.
Temperatures hover around 27–33°C year-round with high humidity. There is no meaningful cool season. Light, breathable clothing and rain gear are the essentials at any time of year.
If you want to witness the equatorial noon shadow phenomenon, time your visit to the March 20–21 or September 22–23 equinoxes. The Kulminasi Matahari ceremony at the monument is worth seeing.