The monsoon regime
Vietnam's climate is marked by the determining influence of the monsoon regime. However, due to the country's length - over 1,600 km between the Tropic of Cancer and the equator - its contrasting topography, with altitudes ranging from 0 m to 3,147 m (Mount Fan Si Pan in the north of the country), and its peninsular nature, which allows the influence of the sea to penetrate deep inland, Vietnam's climate is characterized by irregularity and multiple variations according to local conditions.
The relatively dry winter monsoon, from October to March, moves in from the northeast and affects the region north of Dà Nang, bringing coolness and humidity. The summer monsoon, on the other hand, extends from April to October from the southwest, bringing heat and humidity, especially to the south of the country. These two distinct seasons are subject to regional variations. In addition, temperature and climate vary with altitude: rainfall is more frequent and temperatures drop by 3°C to 4°C on the southern highlands (Dà Lat) and in the mountainous areas of the north. There are three main climatic zones: North, Central and South.
Le Nord
In the north, as far as the Col des Nuages (north of Dà Nang), the four seasons are clearly marked. January to March: a cool winter with drizzle. April to June: a hot, humid spring. July to September: a hot, humid and stormy summer. At the end of summer comes the Ngâu rain, the rain of the 7th lunar month, which for all Vietnamese evokes the legend of the Cattleman and the Weaver. The Ngâu rain is said to be due to the tears shed over their thwarted love. Finally, from October to December: an often magnificent autumn, with the occasional "cloud-shadow rain"(mua bong mây), a brief shower that occurs while the sun is shining and adorns the landscape with sumptuous colors.
In winter (January-March), the temperature in Hanoi can drop as low as 3°C, with the average temperature in the coldest month around 16-17°C. Don't be misled by the figures. We're a long way from polar temperatures, but due to the humidity, the cold is particularly biting and penetrates right down to the bones, especially as homes are rarely heated. From January to April, the weather in Hanoi remains gloomy. A permanent drizzle(mua phun), "dust-rain"(mua bui) or "flying rain"(mua bay) envelops the capital in icy humidity, giving it a characteristic atmosphere.
In the mountains, temperatures are cooler and rain more abundant. Temperatures can drop below 0°C, and snow can sometimes be seen.
Summer is the hottest season of the year. Maximum temperatures can exceed 40°C in Hanoi. But summer is also the rainy season, with maximum rainfall between July and September. There are also frequent thunderstorms and typhoons from the sea, making weather forecasting difficult. Even Hanoi, more than 100 km from the coast, sometimes experiences strong typhoons during the rainy season. These continue their desolate course as far as the mountainous areas of the north-west, where they cause flooding and deadly landslides.
Typhoons
Between July and November, typhoons strike the central and/or northern Philippines from the sea where they originate in the eastern Philippines, causing terrible devastation. The number of typhoons varies from year to year, but it is very difficult to predict the path of these exceptional meteorological phenomena, which are therefore always likely to force travellers to modify their program of activities, particularly sea cruises. In town, avoid driving during typhoons or heavy downpours. Pedestrians and motorists are regularly killed when trees are uprooted by the elements.
Climate change
For millennia, Vietnamese farmers have struggled with the elements and the vagaries of a fundamentally unstable climate. They struggle to cope with heavy rains, torrential flooding and prolonged periods of drought. Today, this vulnerability is further exacerbated by the consequences of global warming. In recent years, meteorologists have been perplexed by the increasing irregularity of monsoons and the multiplication of extreme weather phenomena. Periods of drought are on the increase, sometimes followed by a rainy season in which unexpectedly intense rainfall causes catastrophic flooding. This irregularity of rainfall threatens the survival of the communities affected, and the problems can only worsen as climate change deepens.
