Thailand has a tropical climate and warm sea temperatures year-round, with the rainy season affecting different parts of the country at various times. The water temperature at the surface typically ranges between 27°C and 30°C (81°F to 86°F) year-round. Knowing what the water temperature will be at the time of your trip will help you determine if this is the best time to dive in Thailand.
There are differences, especially during the two rainy seasons, depending on which side of Thailand you visit. Southern Thailand offers two different oceans on either side of its isthmus. On the west side is the Andaman Sea, which is part of the northeastern Indian Ocean. This is where Phuket, the Similan Islands, and Koh Lanta are located. On the east side is the part of the Pacific Ocean known as the Gulf of Thailand. This is where Koh Tao, Koh Phangan, and Koh Samui are located.
Thailand’s average water temperature
You will find below, month by month, the average water temperature in Thailand:
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
| 28°C | 29°C | 29°C | 30°C | 30°C | 30°C | 29°C | 29°C | 29°C | 29°C | 29°C | 28°C |
| 82°F | 84°F | 84°F | 86°F | 86°F | 86°F | 84°F | 84°F | 84°F | 84°F | 84°F | 82°F |
source: seatemperature.info
Phuket water temperature
Below, you will find the average water temperature in Phuket (Andaman Sea), month by month.
These water temperatures can also be used for the Similan Islands and Koh Lanta.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
| 28°C | 29°C | 29°C | 30°C | 30°C | 30°C | 29°C | 29°C | 29°C | 29°C | 29°C | 28°C |
| 82°F | 84°F | 84°F | 86°F | 86°F | 86°F | 84°F | 84°F | 84°F | 84°F | 84°F | 82°F |
source: seatemperature.info
Koh Tao water temperature
Below, you will find the average water temperature in Koh Tao (Gulf of Thailand), month by month.
These water temperatures can also be used for Koh Phangan and Koh Samui.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
| 27°C | 28°C | 28°C | 29°C | 29°C | 29°C | 29°C | 28°C | 28°C | 28°C | 28°C | 27°C |
| 81°F | 82°F | 82°F | 84°F | 84°F | 84°F | 84°F | 82°F | 82°F | 82°F | 82°F | 81°F |
source: seatemperature.info
Other factors, of course, such as rainfall, which impacts the level of visibility underwater, must be taken into account. In this case, it is better to check Thailand climate information.