Thailand's seas are divided into 4 main zones as follows:
1) Andaman Sea Coast: e.g., Phuket, Krabi, Phang Nga, Trang, Lipe Island.
2) Upper Gulf of Thailand Coast: e.g., Cha-am, Phetchaburi, Hua Hin, Prachuap Khiri Khan.
3) Lower Gulf of Thailand Coast: e.g., Koh Samui, Koh Phangan, Koh Tao, Koh Nang Yuan.
4) Eastern Sea Coast: e.g., Pattaya, Koh Larn, Koh Samet, Koh Chang, Koh Mak, Koh Kut.
January - February
- Andaman Sea: e.g., Phuket, Krabi, Phang Nga, Trang.
- Upper Gulf of Thailand: e.g., Cha-am, Hua Hin.
- Eastern Sea Coast: e.g., Pattaya, Koh Larn, Koh Samet, Koh Chang, Koh Kut, Koh Mak.
March - April (Peak season for beach travel - all zones are good)
- Andaman Sea: e.g., Phuket, Krabi, Phang Nga, Trang.
- Upper Gulf of Thailand: e.g., Cha-am, Hua Hin.
- Lower Gulf of Thailand: e.g., Koh Samui, Koh Phangan, Koh Tao, Koh Nang Yuan.
- Eastern Sea Coast: e.g., Pattaya, Koh Larn, Koh Samet, Koh Chang, Koh Kut, Koh Mak.
May - October (Rainy season begins - suitable for the Gulf of Thailand)
- Upper Gulf of Thailand: e.g., Cha-am, Hua Hin.
- Lower Gulf of Thailand: e.g., Koh Samui, Koh Phangan, Koh Tao, Koh Nang Yuan.
November - December (Another high-peak season, almost all zones are suitable. Just check the weather for the Lower Gulf islands like Koh Samui.)
- Andaman Sea: e.g., Phuket, Krabi, Phang Nga, Trang.
- Upper Gulf of Thailand: e.g., Cha-am, Hua Hin.
- Lower Gulf of Thailand: e.g., Koh Samui, Koh Phangan, Koh Tao, Koh Nang Yuan.
- Eastern Sea Coast: e.g., Pattaya, Koh Larn, Koh Samet, Koh Chang, Koh Kut, Koh Mak.