What’s the weather like?The Weather on Koh Tao.

January and February.

Depending on how early or late the November monsoon started will depend on quite how clear the conditions are at the beginning of the year. Traditionally come Christmas the monsoon weather is over and conditions tend to calm down and  open up making the beginning of the year some of the most perfect months of sunshine and flat seas.

January and February are regarded as dry season, which generally means less rainfall and more sunshine. The weather is typically warm and pleasant during these months. Average temperatures range from 25 to 30 degrees Celsius (77 to 86 degrees Fahrenheit), with high humidity.

In terms of diving conditions, January and February are considered a good time for diving in Koh Tao. The seas are usually calm with clear visibility, making it an ideal period for underwater activities. The water temperature during these months can range from 27 to 30 degrees Celsius (81 to 86 degrees Fahrenheit), so a lightweight wetsuit or a rash guard may be sufficient. It’s not uncommon to have some diving days with over 30 meters visibility.

koh Nang Yuan Island
Nang Yuan Island is one of the most beautiful places on earth.


March, April and May.

During March, April, and May, the Gulf of Thailand typically experiences warm and humid weather. The temperatures range from around 28 to 35 degrees Celsius (82 to 95 degrees Fahrenheit) during the day. It is still considered the dry season, with low chances of rainfall, however, it’s worth noting that occasional rain showers or storms may still occur, and they can make for quite the performance some years.

The visibility underwater here in the Gulf of Thailand can vary depending on the location and specific conditions. On average, the visibility ranges from around 10 to 30 meters (30 to 100 feet), with clearer waters generally found further out from the islands.

This time of year is also your best chance of diving with whale sharks. While whale sharks are migratory creatures and their presence in specific areas can be unpredictable, there are certain diving locations in the Gulf of Thailand where whale sharks have been spotted with quite some frequency especially at some of our deeper dive sites around Koh Tao like Chumphon Pinnacle or Southwest Pinnacle. These gentle giants are most commonly seen in the area between March and May, coinciding with their migratory patterns. While encounters cannot be guaranteed, diving during these months increases the likelihood of encountering a whale shark.

Mango Bay on Koh Tao
Crystal clear waters at Mango Bay

June, July & August.

Koh Tao generally experiences varied wind conditions during June, July, and August. These months fall within the monsoon season in the region, which can result in some unpredictable weather patterns. Afternoon storms can be typical, especially in August, but they don’t last long and the weather is still generally pretty sunny throughout the day. It’s important to note that weather conditions can vary from year to year, so it’s always a good idea to check the latest weather forecast before making any plans.

During this time, the prevailing winds in the region tend to come from the southwest, which can create some choppy seas and increased wave activity. As a result, diving conditions may be affected, especially on the west and southwest sides of the island. Strong winds and rough seas can reduce visibility and make it challenging to access certain dive sites. Which is why at this time of year we will often choose sheltered dive sites on the east or southeast side of the island to provide more favorable diving conditions. These sites offer protection from the prevailing winds and tend to have calmer waters and far better visibility during this relatively windy period of the year.

A waterspout forms over Enzo


September and October

September and October are technically the beginning of the ‘winter’ months here on Koh Tao, but you’d never know it. During these months, you can expect variable weather conditions with a higher chance of rainfall. The temperatures in Koh Tao remain warm, typically ranging from 25 to 32 degrees Celsius (77 to 90 degrees Fahrenheit).

The days are beautifully long and sunny. The sea is flat and filled with swimmers and divers. Average daytime air temperatures hover around 30 degrees Celsius, and so does the water temperature. The sea is usually teeming with marine life at this time of year including plankton and krill which brings about fairly regular Whaleshark sightings around the Gulf of Thailand too especially at dive sites like Sail Rock, Chumphon Pinnacle and Shark Island.

a couple sitting at the breaking waves
Windy weather on Koh Tao

November and December.

These are considered the wettest months in this region, with an increased chance of rainfall and occasional thunderstorms. The weather can be unpredictable, with both sunny and rainy days. The temperature typically ranges between 25°C (77°F) and 32°C (90°F). The sea conditions around Koh Tao are affected by the monsoon season when visibility decreases due to the runoff from rain and increased sedimentation. However, the water temperature remains warm, usually around 28°C (82°F).

While the weather and visibility might be less favorable compared to other months, diving is still possible during the heavy monsoon conditions. Big Blue Diving continues to operate during this time, offering trips to dive sites on the sheltered west side of Koh Tao, to avoid the large waves and the unpleasantness of seasickness!

Remember, weather patterns can change from year to year, so it’s advisable to check the latest weather forecasts and consult with us  or follow us on our social media platforms for the most up-to-date information on weather and diving conditions and the likelihood of spotting whale sharks in the Gulf of Thailand during your intended diving period. We will be able to provide you with specific details based on current observations and trends.

moody waters
Monsoon season starts in November but is usually over by Christmas.