Vietnam is entirely located in the tropical belt lying between the equator and the Tropic of Cancer. While there are slight variations in temperature, depending on the season and the altitude, the primary seasonal changes are marked by variations in rainfall.
In the north, the rainy season extends from mid-April to mid-October; the city of Hanoi has a mean annual rainfall of 172 cm (68 in), and in the mountains, annual rainfall sometimes exceeds 406 cm (160 in). Daily temperatures fluctuate considerably in the Red River Delta region, particularly in the dry season, when the thermometer may drop as low as 5° C (41° F ) in the region of Hanoi. During the rainy season, the average temperature in Hanoi is about 30° C (86 F ).
The south is more tropical; temperatures in Ho Chi Minh City vary only between 18° and 33° C (64–91° F ) throughout the year. Temperatures in the Central Highlands are somewhat cooler, ranging from a mean of about 17° C (63° F ) in winter to 20° C (68° F ) in summer. The rainy season extends from early May to November, with annual rainfall averaging about 200 cm (79 in) in lowland regions. The typhoon season lasts from July through November, with the most severe storms occurring along the central coast. Typhoons in this region frequently lead to serious crop damage and loss of life.