The country of Vietnam experiences multiple tornadoes annually. Between 1993 and 2000, there are a total number of 317 tornado occurences in the country. Most of these tornadoes bring F1 intensities in the Fujita scale (F scale), but a very few documented tornadoes are able to reach F3 intensities. They typically form during severe thunderstorms or typhoons. To date, studies that involve the country's tornado climatology are limited.
A tornado, also known as vòi rá»Âng or lá»Âc xoáy in Vietnamese, is a violently rotating column of air that descends from the base of a thunderstorm onto the ground. They are usually accompanied by thunderstorms or brought by typhoons. Tornadoes are associated with strong atmospheric instability, a characteristic of the rainy season. Weather fronts often increase the formation of tornadoes, when warm, most air is pushed upwards and collide with the cold, dry air, which then cools and condenses into moisture that triggers the formation of thunderstorms.
The country has a tropical climate that is influenced by monsoons. It has two distinct seasons: the dry season and the rainy season. The transitional periods of these seasons are favorable for tornadoes as atmospheric circulation provides the necessary conditions for severe weather events to develop, with it being the months from April to May in the north and May to August in the south.
Tornadoes appear in almost every region in the country, with most tornadoes located in Southern Vietnam, followed by Northern Vietnam, and lastly Central Vietnam with the least amount of tornadoes reported. These tornadoes occur most frequently in May around the country. In the north and central regions, high concentrations of tornadic activity appear from March to May, with April being the most frequent. Meanwhile, tornadic activity in the southern regions span from June to August.
The country's meteorological agency, NCHMF, stated that it's difficult to forecast tornadoes with accuracy due to their small size and duration. Instead, they can only issue general warnings when conditions are favorable for tornado development. Unlike storms and typhoons which can be monitored through radar, tornadoes appear suddenly in small areas and can only be detected through direct observation.