Guide Travel of Thailand.

Southern Thailand Southern Thailand's seasons are less distinct and really there are only two proper seasons - summer and the rainy season. The Gulf of Thailand lies to the east of the Thai peninsula while the Andaman Sea lies to the west. Visiting areas west of the peninsula (Phuket, Phang Nga, Krabi) is best done between mid November and April to avoid the monsoons that occur during other months - monsoons obviously make visiting islands by boat difficult and sometimes dangerous. Clearly they are best to be avoided. Areas east of the peninsula (Koh Samui, Hat Yai) are best visited from December to June. However, visiting the Gulf of Thailand region is possible throughout the year but those going to this region should check the current weather situation to avoid rain. If you are planning to visit both sides of the coast during your stay in Thailand, December to April would be best.