The winter season is undeniably the best time for visiting. The weather is dry and comfortably hot. The high makes +28–31 °С during the day. It drops down to +21-23 °С at night.
It is mostly sun with occasional raining (it is very rare). Low humidity helps fight the heat and it is pleasantly warm outdoors. This period is called the "high season" because the capital is visited by tens of thousands of tourists.
March is dry and hot in Bangkok. The weather is sunny and fine. The average makes up to +33 °С during the day (+25 °С at night). It seldom rains and the level of humidity is low. This helps fight the heat.
April and May are very hot in the capital of Thailand. The thermometer can reach up to +35 °С or even more than +40 °С. Expect weak to none precipitation. It starts raining in the end of May. It is the very beginning of the raining season that can last up to the middle of September. The weather becomes stuffy and moist during this period.
It is a bit less hot in June, when the thermometer shows +32–33 °С during the day (+25-26 °С at night). However, the weather is still rainy. The raining season is in full swing, meaning that showering with thunderstorms is frequent. In fact, it can rain day after day. Precipitation makes the weather less stuffy and hot, giving a short break from scorching heat.
The weather is almost identical in June and July. August is one of the rainiest months of the year. It can pour almost every day (rains usually last for one hour). It will not spoil your vacation because the weather gets sunny again several minutes after it stops raining. However, the sky can remain clouded for the rest of the day on some occasions. The temperature makes up to +32 °С during the day. Expect +24 °С at night.
The peak of the raining season falls on September and October, meaning that it showers hard in Bangkok during this period. However, this does not mean that it rains every day. The rains are more frequent, often with thunderstorms or squalls. The weather is cloudy. The level of humidity increases as well. The high is +31–32 °С (+24-25 °С at night).
It rains less often in November. The raining season ends in the middle of the month. The weather is dry and warm. It is excellent for exploration of the city. The thermometer shows up to +31 °С (+23 °С after sunset).