If you look in the map you can see that Thailand is largely tropical. The temperatures throughout the year are between 30-40 degree Celsius or between about 85-105 degree Fahrenheit. So it is pretty hot plus humid all year around. If you want a nice cool air, you will find that only in the mountains in the far north of Thailand.
There are only 3 seasons in Thailand: Cool, Hot, and Rainy or some Thais call Hot, Hottest, and Hot with Rain.
Cool season begins from November to about the end of February. This is the only season you will get to feel nice fresh cool air. It is the most popular time to visit the country and the air tickets, hotels and a tour packages are at their peak price rate and very difficult to find. However, when we say it’s a cool season, you might not even notice it in the South of Thailand but it just doesn’t rain as much as in the other seasons. And in the north where the mountains are, the temperature will drop as far as to 0 degree Celsius or a little beneath that which you will need only a good sweater.
Hot season or summer! The season starts in March and finish in June or July. And be careful if you cannot stand the hot weather because the temperature will rise as high as 40 degree Celsius or 104 degree Fahrenheit. But I find this season really good and pleasant especially for Thai people to go to the beach sit with a cold drink and swim in the sea.
Rainy season is between July and October. The monsoons hit most of the country especially in September and early October. Flooding is something you can expect in this time of a year.
Next time you plan a trip to Thailand, I recommend you to concern about the climate so that you can enjoy the best of Thailand.