September sees parts of South East Asia in high season. September is one of the best times of year to visit Bali, Lombok and much of Indonesia with very low rainfall and long clear sunny days. Prices in Bali often drop from the middle of September.
Borneo and the East Coast of Malaysia are also in high season and usually see very little rainfall and long sunny cloudless days.
Although much of Thailand is under the influence of the South East monsoon, Koh Samui and Koh Phangan in the Gulf of Thailand are in high season, characterised by lower rainfall and plenty of cloudless, sunny days.
Elsewhere in Thailand, great value can be found for beach holidays to Phuket, Khao Lak, Koh Lanta and Krabi which are likely to see some rain at this time of year (but usually in short, intense afternoon downpours).
Central Vietnam has generally dry conditions in September, making Hoi An a good choice for a Vietnam beach holiday.