Luckily for tourists, Tioman is open all year round because its tropical climate remains fairly consistent throughout the year. There is a distinct monsoon season, however, which affects the island from September to November and February to March. "Summer" time on Tioman starts from April through to August.
Tioman sees a peak in visitors during long Singaporean and Malaysian holidays, such as Chinese New Year and Hari Raya, and especially in November and December, which are the school-free months.
Beware that if you choose to come during the monsoon season, there is a small chance of getting marooned on the island as the ferries will not be able to ply the Mersing-Tioman route due to dangerous waters.