Indochina Weather and Climate

Vietnam, Laos and Cambodia, all three countries are often grouped together under the name Indochina. Over most of Indochina there is a single rainy season at the time of the south monsoon between May and September.

Indochina has a tropical monsoon climate dominated by south to southeasterly winds from May until September and northerly to northeasterly winds between October and April. There is a twice-yearly period of variable winds at the time of transition from the north to south monsoon.

During the rest of the year rainfall is infrequent and light. Annual rainfall is almost everywhere above 1,000 mm/40 in, and rises to between 2,000 mm/80 in and 2,500 mm/100 in on the hills, particularly those facing the sea.

On the coast and in those parts of the central highlands that face northeast, the season of maximum rainfall is between September and January. This area often receives heavy rain from typhoons, or severe tropical storms, which develop in the western Pacific at this time of year. This is also a time of much cloud and frequent drizzle (called locally the crashing).

In the north of Indochina there are more cloudy days with occasional light rain during the period of the northeast monsoon. The south of this area is more likely to be dry and sunny at this time.

In the southern and central parts of Indochina, temperatures remain high around the year, but in the north there is a definite cooler season as the north monsoon brings colder air from central China from time to time.

Frost and occasional snow only occur on the highest mountains in the north for a few days a year. In the south of Vietnam, and in Cambodia and Laos, the lowlands are sheltered from any such outbreaks of colder northerly air and the dry season is warm to hot with much sunshine.

The weather of Vietnam, Laos, and Cambodia is rather sultry and oppressive during the rainy season and the humidity is high at this time. On the coast and in the hills the frequent cloud and high humidity combine with lack of sunshine to make this time of the year rather unpleasant in spite of the reduction of temperatures with height.