Kuantan sits on Malaysia's east coast, which means it gets the full force of the northeast monsoon from late October to February. During these months, rainfall can be heavy, the sea is rough, and Teluk Cempedak beach is not worth visiting. The rest of the year — March through October — is warm, humid, and generally fine, with the driest and most reliable weather between March and September.
July and August are peak season for the lotus bloom at Lake Chini. Sea turtles nest on certain east coast beaches from May to August (though not typically at Teluk Cempedak itself). If you are coming primarily for the beach, target May to September and check the monsoon forecast before booking anything non-refundable.