Best time to travel to Borneo
Borneo has tropical climate. Usually before or after the rainy season the weather is pleasant to travel to Borneo.  

During July and August and sometimes up to October there have been forest fires reported  in different parts of Borneo affecting the air quality. It is highly recommendable to find out about possible fires in Sabah, Sarawak or Kalimantan through your country's embassy before you travel.