The dry season runs from roughly November to May, when the east coast of Negros receives its best weather: low humidity, minimal rain, and calm seas that make the boat ride to Apo Island a pleasure. February and March sit in the sweet spot — dry and not yet hot. April and May are warm but still manageable, and the sea stays calm.
The wet season from June to October brings rain, humidity, and the risk of typhoons. Negros Oriental sits in the typhoon belt, and serious storms can affect the island between July and October, occasionally disrupting ferry services and making coastal travel difficult. The rain also turns mountain roads slippery, which complicates trips to the Twin Lakes and Casaroro Falls.
Diving is viable year-round at Apo Island — the marine sanctuary is sheltered enough to dive on most days outside of active storms — though conditions are best from November through May when visibility is highest and currents are predictable. Dauin's muck diving is less weather-dependent and can be excellent at any time of year.
There are no major festivals that should drive travel timing, but the Buglasan Festival of Festivals in October, held in Dumaguete, is worth knowing about if you happen to be there: a week of street dancing, music, and competitions drawn from festivals across the province.