Thailand in a Nutshell
Hosting divers in both the Andaman Sea and the Gulf of Thailand from over 1200 miles of coastline, this scuba destination is a great fit for divers of any level.
Marine Highlights from Thailand's Andaman Sea
Dive conditions vary depending on what area of Thailand you chose to go. Within the Gulf of Thailand, diving is available almost year round. November is the beginning of the monsoon season in which visibility drops and heavy rain storms can occur but by the mid/end of December things typically have gone back to normal. On the Andaman side, dive times are more limited. Some areas are only available to dive parts of the year (like the Similians and Koh Lanta). In general October - April is the best time to dive the Andaman Sea.
In general the Andaman Sea boasts a larger variety of fish species and coral. As to what you can expect to see - the coastline and islands stretch over a large distance so it greatly depends on where you choose to dive. Manta rays, whale sharks, black/white tips, and turtles are just a few of the "big things" to expect. As tourism in Thailand is becoming more and more popular, I would highly advise a trip sooner rather than later - as some dive destinations are already becoming a little overcrowded.
Liveaboards are available to explore the Andaman Sea and reach dive sites you otherwise can't reach, but they limit your freedom in exploring what else Thailand has to offer. An alternative is to "island-hop" to different destinations comparing the local reefs and their offerings. Every island has its own personality, so depending on what you are looking for... certain islands would fit best. Looking for a night on the town? Koh Phi Phi on the Andaman side, or Koh Tao in the gulf would be a good start. Prefer a relaxing evening instead? The Andamans, Koh Lanta, or Koh Samui in the gulf could be better alternatives.