Despite being a small region, the climates of Southeast Asian countries are incredibly diverse and rich. Weather conditions vary at different times, and even within the same period, weather can differ significantly in different locations.

Bali, Indonesia
Best time to go: from April to October. The average temperature ranges from 24 to 30 degrees Celsius, and the weather is quite dry. Especially, from July to September is the peak tourist season, so prices for food, transportation will be higher than usual.
Rainy season: from December to February. During these months, the average rainfall is about 309mm. Because of frequent rain and wind, this is the low season, and you can save on expenses.

Malaysia
Best time to go: from January to March and from June to September. Malaysia is located near the equator, so the weather is hot and humid throughout the year. However, these are the times when the average rainfall is lowest.
Rainy season: from October to December. Monsoon winds will continue until February in Borneo.

Singapore
Best time to go: from January to October. Similar to Malaysia, the weather in the Lion City is relatively stable throughout the year with temperatures ranging from 30 to 33 degrees Celsius. From June to August is the driest period.
Rainy season: from November to December, with an average rainfall of 250mm per month.

Thailand
Thailand, known as one of the largest countries in the region and influenced by the Gulf of Thailand and the Andaman Sea, experiences varying weather throughout the year.
Bangkok
Best time to visit: November to January is the prime time, with an average temperature of around 20 degrees Celsius. From February to May is relatively dry, but humidity gradually increases.
Rainy season: from June to October
Chiang Mai
Best time to visit: from November to February. This second-largest city in Thailand experiences significant temperature differences. Temperatures drop to around 15 degrees Celsius at night but rise to 30 degrees Celsius during the day. In March and April, temperatures range from 25 to 40 degrees Celsius.
Rainy season: from May to October.
Koh Samui
Best time to go: from April to September and from January to March.
Rainy season: from October to December. This is the time when it rains almost all day.
Phuket

Best time to go: from November to February is the ideal time for travel, with daytime temperatures around 30 degrees Celsius and slightly cooler at night, around 23 – 25 degrees Celsius. From March to May is quite hot. However, this is not a big issue because you can always head to the beach anytime.
Rainy season: from May to October. Characterized by sudden but short-lived downpours. You can take advantage of this time to negotiate prices with resorts/hotels.
Vietnam
Similar to Thailand, Vietnam also has 3 different climate zones. Hanoi is very cold in winter, Ho Chi Minh City experiences monsoon winds, and the Central region has relatively pleasant weather throughout the year.
Central Region (Danang, Hoi An, Hue, and Nha Trang)
Best time to go: from January to May. This is the driest time of the year with an average temperature ranging from 21 to 30 degrees Celsius. From June to August, it is hotter and more humid.
Rainy season: from June to July and from September to November in Danang. From October to early December in Hue, Hoi An, and Nha Trang.
Hanoi
Best time to go: Spring (March – April) and Autumn (October – December) are the most pleasant times of the year with temperatures ranging from 18 to 25 degrees Celsius. In winter (January, February), daytime temperatures can drop to 12 degrees Celsius. The climate is cold but relatively dry.
Rainy season: from May to September. During these summer months, temperatures can rise up to 40 degrees Celsius.
Ho Chi Minh City

Best time to go: from March to May, the weather is hot and dry with an average temperature of 32 degrees Celsius. From December to February, the weather is cooler with daytime temperatures ranging from 20 to 30 degrees Celsius.
Rainy season: from late May to early November.
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Source: Travel Guide by Mytour
MytourAugust 26, 2013