Thailand has three seasons. The cool season (November–February) is the best time to visit: temperatures are 25–32°C, humidity is lower, and rain is minimal. The hot season (March–May) is brutal, reaching 38–40°C in Bangkok.
The rainy (monsoon) season (May–October) brings heavy afternoon showers but also lush landscapes and fewer crowds. The Gulf of Thailand coast (Koh Samui, Koh Tao) has a different monsoon pattern, with heavy rain October–December instead. The Andaman Coast (Phuket, Krabi) is best November–April.