Koh Tao in August

February through May offers the best diving conditions – calm seas, excellent visibility, and the highest chance of whale shark encounters. The water temperature stays around 28°C, perfect for diving in just a wetsuit. But this is also peak season, so expect crowds and higher prices. September and October are the sweet spot for budget travelers. The rainy season is ending, accommodation prices drop by 30%, and the diving is still excellent. You might get a few afternoon showers, but they usually pass quickly. Avoid November through January if possible. The northeast monsoon brings rough seas and limited ferry schedules. Many dive shops close during the worst weeks in December, and you'll be stuck on the island if storms cancel the boats. Here's the thing about Koh Tao's weather – it can change fast. Even during the dry season, afternoon thunderstorms pop up out of nowhere. Always check the marine forecast before booking diving trips.