Northern Vietnam - has two distinct seasons - hot and humid summers (vary from 24 to 41 oC)  and cool and dry winters (vary from 16 to 23 oC).

Central Vietnam - coastal areas are more temperate than the sticky south (although they do experience high rainfall), while the Central Highlands are pleasantly cooler. The weather is also hot and reasonably dry from May to September. The monsoon winds then change bringing above average rain during late September.

Southern Vietnam - is fairly consistently hot and humid all year round. May - November, from 24 - 41 oC Winter: December - April, 22 - 33oC

See also other FAQs

What is the best type of clothing we should bring?

How cold can it get in the winter?

How hot is that in the summer?

What is it this like to travel in monsoon season; will it cause trouble for us?