The climate of Vietnam is a bit complicated. Though it lies in the tropics, the significant variations in latitude and altitude in the country produce varying climate situations. You should therefore prepare accordingly for the specific region where you think you’d be spending most of your time.
North Vietnam has only two basic seasons for the year: a humid and frigid winter with a temperature of around 5 °C (41 °F) from the months of November to April, followed by a wet and warm summer for the rest of the calendar year. Temperatures during the summer reach around 37 °C (98.6 °F). Expect, too, some occasional typhoons to make things interesting for your vacation.
On the other hand, South Vietnam is generally warm the whole year, with the temperature playing just between 21 °C (69.8 °F) and 28 °C (82.4 °F). May to March is the hottest period in this part of the country. Temperatures during this period can reach as high as 30°C. This is followed by the monsoon season, spanning the months of April to October.
A trip to Vietnam in late January or early February will allow you to participate in Tet, the most important festival in Vietnam. Marked by both festivity and meditation, this week-long celebration ushers in the new lunar year and spring.