Vietnam - Weather and Climate

Vietnam’s weather varies from the sub-tropics in the North to the tropics in the South. The humidity is high, with average ranging around 84% a year. Moderated by two monsoons, the average temperature (from 22 to 27) is lower than other countries also in the equatorial regions. The weather varies greatly from North to South, depending on elevation and type of landscape.
Vietnam is located between 9 and 23 degrees north. Eastern Vietnam has a long coastline on the Gulf of Tonkin and the South China Sea. It has a tropical monsoon type of climate; from May-Sep the south monsoon sets in, and the country is dominated by south to southeasterly winds. From Oct-April, the north monsoon is dominant with northerly to northeasterly winds affecting the country. There is a transition period between each monsoon season when winds are light and variable.
The country is mountainous in the northwest and in the central highlands facing the South China Sea, with peaks reaching up to 8000ft (2450m) In the north around Hanoi and in the south around Ho Chi Minh City, there are extensive low-lying regions in the Red River delta and the Mekong delta respectively.

Northern Vietnam (from Hue up North) has four seasons with a cold winter and hot summer. The temperature ranges from 5-6C in winter to up to 35C in summer. The further North it is, the colder it gets. In mountainous regions in the far North (such as Sapa) the temperature sometimes drops below zero. Rainy months are August, October, November. February and March have persistent, light, drizzling rain. The northeast monsoon effects the north bringing lower temperatures to Hanoi, Ha Long Bay, Sapa and the the coastal strip as far south as around Hue. Temperatures only drop to what could only be considered cool in Hanoi, the mountainous north and the Central Highlands (in the evening). For the majority of the country, the temperature swings between the mid 20s to low 30s year-round.

Temperatures of Central Vietnam are high all year round. The temperature tends to be warmer and more humid than the South in the middle of the year and cooler during the dry season from November to April. Flooding may occur from October to December. The southwest monsoon brings primarily effects Southern Vietnam -- warming up the Mekong Delta through Saigon and all along the coastal strip as far north as between Qui Nhon and Da Nang. It also covers the Central Highlands region. 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 mua bui, sometimes crachin).

Southern Vietnam has a distinct dry season (from November to April) and wet season (from May to October). Average temperature ranges from 25-30C. During wet months, heavy and short downpours may occur in mid-afternoons. The general features of the climate of VietNam also apply to the two adjoining countries, Laos and Cambodia; all three countries are often grouped together under the name Indo-China. Over most of Indo-China there is a single rainy season at the time of the south monsoon between May and September.

Water is VietNams most important factor for domestic use, animal feeding, cultivating and for industrial production. Being a tropical, monsoon and redundant rainfall-country, Viet Nam has a blooming agriculture, especially in water rice cultivation. Recently, yielding the 'doi moi' policy, and modern technology, agricultural extension and agriculture production achieve number of valuable results. From a country which had to import food stocks in the past, VietNam is now becoming the second country in the world for food stocks exporting. Agriculture extension and yield improvement for rice as well as for other crops require water irrigation at right cropping time, with proper quantity and good quality due to crop water requirement.

According to geographical and climatologic conditions, rainfall distribution in VietNam is not equal both in space and time; the difference amount of rainfall between high-rain area and low-rain area is tremendous; in high-rain area, annual amount of rainfall may reach to 5000 mm while 800 mm in low-rain area. This is one of causes of drought. Recently, climate changes and environment deterioration by human which cause protective forest destruction, surface and ground water reduction and result in drought. Thought must be given to the role of water in agriculture production, the State of VietNam pays much attention to water resources construction to take part in agriculture development, to hold fast the food security of country, to solve the problem of clean water for people and animals in mountainous area and in frequent-drought area. With the support of the UNDP Ha Noi - a United Nations Agency, and the former Ministry of Water Resources (the Ministry of Agriculture and Rural Development instead), 'Strategy and Action Plan for water disaster mitigation in VietNam' has been built and participated in water disaster mitigation in VietNam.

Reference:
http://www.vietnamembassy.org.uk/climate.html
http://www.travelfish.org/vietnam-weather.php
http://www.wompom.ca/vietnam/vnclimat01.htm