The best time to visit Sabang Island is November to March, when the seas on the western side of Sumatra are calmest and underwater visibility for diving and snorkelling is at its peak — often 15–25 metres. April and May can also be good, with less rain than the transition months.
June to October brings rougher seas and reduced visibility around Iboih and Rubiah Island, though diving is still possible on more sheltered sites. The island is relatively close to the equator and has no true dry season, but the northwest monsoon (November to March) generally favours the western coast, which is where the main dive sites are.