There are various methods to assess the wind levels in atmospheric disturbances in the Western Pacific. The understanding presented below is commonly accepted and applied by reliable meteorological agencies such as Japan, Hong Kong, and the United States.
Distinguishing Storm Levels
According to the regulations set by the Western Pacific Typhoon Centers (the area including Vietnam).
- If wind speeds do not exceed 63 km/h, it is referred to as a tropical depression.
- If wind speeds range from 63-88 km/h: tropical storm.
- If wind speeds range from 89-117 km/h: severe tropical storm.
- If wind speeds are 118 km/h or higher: typhoon.
Satellite image map capturing a storm.
In the same Western Pacific region, according to the regulations of the U.S. Navy’s Joint Typhoon Warning Center based in Guam, when a typhoon reaches wind speeds exceeding 115 knots (213 km/h), it is classified as a super typhoon.
For the Saffir-Simpson scale used for the Atlantic and Eastern Pacific regions, when a storm reaches wind speeds above 117 km/h, it is categorized into five levels based on wind speed. Accordingly, at level 1, maximum wind speeds range from 118 – 153 km/h; level 2 (154-177 km/h); level 3 (178-209 km/h); level 4 (210-249 km/h); and level 5 (over 250 km/h), categorized as a “super typhoon” due to wind speeds exceeding 249 km/h. Another criterion is that when the pressure drops below 920 hPa, it is classified as a super typhoon.
Structure of a Typhoon
The main components of a typhoon include the rain bands on the outer edges, the eye of the storm in the center, and the eyewall located immediately adjacent to the eye. In the lower half of the atmosphere, air spirals inward towards the center in a counterclockwise direction, rising vertically inside the eye of the storm and spreading outward at the top in the opposite direction. At the center of the typhoon, the air descends, creating the clear area in the eye of the storm.
Eye of the Typhoon
The eye of the typhoon is a relatively calm area, free of clouds, with a diameter of about 30-60 km. When inside the storm area, people are often surprised to see the strong winds and heavy rain suddenly cease, and the sky becomes clear; this indicates that the eye of the typhoon has passed.
Figure 2: Diagram of typhoon structure with basic components: eye, eyewall, and spiral rain bands.
Eyewall
The eyewall is the thick wall of clouds surrounding the eye of the typhoon, consisting of towering cumulonimbus clouds. This is where the strongest winds in the storm occur.
Spiral Rain Bands
The rain bands on the outer edges of the typhoon can extend hundreds of kilometers from the center. These dense bands of clouds rotate slowly in a counterclockwise direction, ranging in width from a few kilometers to several dozen kilometers and stretching approximately 80 to 500 km long.
Size of a Typhoon
The typical size of a typhoon is a few hundred kilometers, but it can vary significantly. The size of a typhoon does not necessarily indicate its intensity.
