Although there are peak months in terms of tourism (May – September), it is advisable not to put too much emphasis on weather prospects when planning a trip to Borneo!
Weather conditions are localised and complicated throughout Borneo, with one region receiving its highest rainfall of the year whilst another is dry as a bone. As with all tropical islands, climates are unpredictable and rainfall can occur at any time of year, with weather conditions often changing very quickly and showers turning to sunshine or vice versa in a matter of minutes.
Borneo benefits from year-round temperatures averaging between 27°C & 32°C, with a relative humidity of around 80% for much of the year.
Rainfall can exceed 4,000mm per year in pockets of Borneo, although in most destinations an average of 220mm per month is the norm. Generally speaking a peak in rainfall occurs between November and March, although even in these months rainfall can be sporadic, and it is difficult (in fact impossible) to pre-determine which will be the wet weeks and which will be the dry.
Furthermore there are many benefits of lower visitor numbers to be enjoyed in the traditionally wetter months, and the National Parks, wildlife sanctuaries, jungle lodges, caves and dive sites may be far more appealing with fewer fellow visitors to share your experiences with.