For the average traveler Borneo is a place to visit any time of the year. For those with interests in extensive jungle trekking, diving, and golfing, the rainy season comes with notable disadvantages.
Wet and a dry season distinguish periodic weather conditions on Borneo. The average rainfall during the wet or rainy season is higher than during the dry season. However, there are places, where you hardly note the difference.
Furthermore, Borneo is the world’s third largest island. Wet and dry seasons do not occur in every part at the same time. In Kuching for example the wet season lasts from November to February and the dry season from June to August. In Kota Kinabalu, the driest months are February and March and most rainfall appears in the months around October. In Pontianak, Indonesia, most rainfall appears from October to December however, the wet season is not as distinctive as in the Malaysian part of Borneo. For the latest weather forecast and further research on the monthly average rainfall, the following direct links to worldweather.org provide detailed information for selected cities:
Tourists should consider that there are days without rain during wet season and occasionally heavy rainfalls during dry season. However, due to the rough sea during the rainy season diving is not possible everywhere throughout the year. Camping in the jungle for several days during wet season will not be a pleasure for tourists. It might rain for weeks. However, this should not keep anyone from a one day hike or an overnight stay in the rainforest.
Light summer clothes are fine any time of the year. Days without sunshine are rare and usually it rains once a day. Rather than to carry an umbrella around a rain poncho is practicable for travellers who are surprised by a downpour. Due to extensive air-conditioning, visitors are more likely to feel cold in public buildings and restaurants then in open areas. On a rainy day during the wet season, temperatures might drop to 19C in the evening. A sweater or a light jacket is advisable.
For visits to caves, highlands or Mount Kinabalu National Park specific requirements for clothing apply.