Vietnam
Vietnam's weather is comparable to Cambodia's, with year-round temperatures ranging from 25-30 °C (77-102 °F).
The rainy season in this area usually takes place between June and September, where short but intense showers are common; however, the sun will often break through for extended periods of time allowing people to enjoy the outdoors in spite of the rain.
From the end of March to May, right before the monsoon season arrives, Vietnam and Cambodia experience a particularly hot and humid climate with temperatures soaring up to 40 °C (Around 104 °F).
Cambodia
Cambodia is located in the tropical climate zone, in which neither the temperatures nor the hours of sunshine show great variations over the course of the year. Due to the tropical monsoons in Cambodia, a distinction is made between a dry season and a rainy season, and each of these seasons has its own charm.
The dry season runs from October to April and is the time to visit the coastal towns of Cambodia or the tropical islands. The temperatures are warm and comfortable during this time of year, and there are long periods of sunshine. Although it is relatively dry during this time, individual showers can occur.
The rainy season runs from May to September and is ideally suited to experiencing Cambodia’s nature in a particularly green and lush way. The warm temperatures remain unchanged, while the rain ensures high humidity. There is a lot of rainfall, especially in the last months of the rainy season. For the entire time, however, the rain falls in short downpours.
While Cambodia can be visited year-round, it is important to note that small country roads that may pass through the more remote areas, e.g., the province of Mondulkiri, are impassable during the last two months of the rainy season.
Laos
Laos typically experiences hot and humid weather throughout the year with temperatures ranging from 28°C to 34°C during the day. The temperature usually drops at night, and during winter months in the mountains, it can sometimes even dip as low as 10 °C. Despite its tropical location, Laos can still get surprisingly cold due to its high altitude.
The climate of the region is mostly dry during the period between October to April, while the rainy season tends to start in May to September. During this period, heavy downpours are common, but with brief periods of bright sunshine in between.