About the climate and weather in Thailand many errors are spread.
Still most tourists visit the West Coast around Phuket and Koh Phi Phi.
Around 1990 this was almost the only area which was developed for tourism.
Therefore, most travel guides and climate tables are from that region.
There are three different climate zones in Thailand: The North, the West Coast and the East Coast. The three of them have completely different seasons. A rainy month at the West Coast can be beautiful at the East Coast. For example May is one of the best months on Koh Tao - but people think May is rainy.
We locals say: "Koh Tao is so small, it is overlooked by the rain." Even in months with lots of rainfall at the East Coast there is significantly less rain on Koh Tao than on Phangan or Samui.
The seasons on Koh Tao
Click for large picture.
The rainy season at the East Coast was the last years end November/ beginning December.
Than the dry season starts, the transition usually lasts till middle/ end of January.
The warmest months are March and April.
May is pleasantly warm with little rain.
In June the weather at the West Coast is bad, but Koh Tao mostly just gets some wind and rain showers.
In mid-July the weather stabilizes and normally the entire summer is very nice.
Even October and the beginning of November is usually very sunny.
Then the year starts again :-)