Digital Typhoon: Typhoons, Hurricanes and Cyclones

Typhoons, or tropical cyclones, have various names depending on their birth places in the world. Let's compare the differences among them.

What is called a typhoon in the western north Pacific and Asia (Japan) is called a hurricane in north and central America, and a cyclone in other areas of the world. They can be classified into the same meteorological phenomenon in the sense that all have the same type of structure as a tropical cyclone. The following summarizes typhoons worldwide and some of the related terms in more detail.

Term	Meaning
Cyclone [Generic term for a low-pressure system]	Cyclone is a generic term to refer to a low-pressure system. Typhoons and other types of low pressure systems are all cyclones. The direction of rotation is opposite in the northern hemisphere and the southern hemisphere, but other essential features of a cyclone are shared in both hemispheres.
Tropical Cyclone	Tropical cyclone is in general a cyclone formed in the tropical areas. However, the word "tropical" does not refer to the place of formation, and it actually refers to the structure of a cyclone. This means that a cyclone with the structure of a tropical cyclone is called a "tropical cyclone" regardless of the place. Typhoons, hurricanes and others are all "intense" tropical cyclones, so they are regarded as same meteorological phenomena (classification of intensity). A unique convention for tropical cyclones is that each tropical cyclone is named.
Extratropical Cyclone	Extratropical cyclone literally means a cyclone outside of the tropical areas. Most of the low pressure systems that pass around Japan belong to this type. Just like a tropical cyclone, this term also does not refer to the place of formation, but refers to the structure of a cyclone. The fundamental difference between a tropical cyclone and this type is that the former consists of warm air only, while the latter consists of both cold air and warm air. This difference also leads to the different source of energy for intensification. Finally, we often see a tropical cyclone transformed into an extratropical cyclone, but the inverse is rare.
Typhoon	Typhoon is a tropical cyclone located in the western north Pacific basin (between 100E and 180E in the northern hemisphere). The category of a typhoon is decided by the maximum sustained winds, but please note that the typhoon in Japanese standard and the typhoon in international standard is not the same. Finally, among tropical cyclones in the world, the typhoon is the most frequent and the strongest tropical cyclone. Typhoons are named.
Hurricane	Hurricane is a tropical cyclone located in the north Atlantic, eastern north Pacific (east of 140W in the northern hemisphere), and central north Pacific (140W to 180W in the northern hemisphere), eastern south Pacific (east of 160E in the southern hemisphere). The category of a hurricane follows the same international standard as the typhoon based on the maximum sustained wind. When a hurricane reaches the 180E (180W) degree line and enters into the basin of the typhoon, it starts to be called a typhoon. Hurricanes are named.
Cyclone [Abbreviation of a tropical cyclone]	Cyclone is a generic term for a cyclonic system, but the same word is also used as an abbreviation of 'tropical cyclone' as long as a special term to represent a tropical cyclone does not exist. In northern Indian ocean (west of 100E), the term "cyclonic storm" is used, and in southern Indian ocean, around Australia, and in the southern Pacific ocean, the term "tropical cyclone" is in use. If a typhoon moves westward to pass 100E, then it starts to be called as a cyclone. It seems that the first tropical cyclone in the south Atlantic in 2004 is called either a cyclone or a hurricane. Cyclones are named.
Willy-Willy	Willy-Willy is often introduced as the name of a tropical cyclone around Australia, but it seems that it actually means something like a dust devil, and has little relationship with a tropical cyclone. Additional information.
Tornado	The tornado (waterspout or whirl wind) and the tropical cyclone share the same feature as the low-pressure vortex of atmosphere, but other features, such as formation, structure, scale and duration, are totally different. For example, the scale of a tornado is usually on the order of 100m-1000m, while a tropical cyclone is on the order of 100km-1000km. In some cases, however, a tropical cyclone spawns a tornado due to the severe weather and produces irregularly strong winds beyond expectation.

Relationship among terms above can be summarized as a hierarchical classification as follows.

Does this mean that "Typhoon" and "Hurricane" are the same phenomena - just their difference is in the location of the storm? The fact is a little more complicated, because the difference is also in the intensity. In Japan, the word "Taifu" or "Taihu" (the Japanese word for "Typhoon") has a slightly different meaning. As the following table shows, the difference of "Taifu" and "Typhoon" is in the intensity, while the difference of "Typhoon" and "Hurricane" is in the location.

Location	Max. Wind 34-64 knots	Max. Wind 64- knots
Western North Pacific Region	Taifu (Taihu)
Western North Pacific Region	(Severe) Tropical Storm	Typhoon
North Atlantic Basin	Tropical Storm	Hurricane

The following table summarizes the detail of the classification of tropical cyclones. As the classification of typhoons shows, "tropical storm + severe tropical storm + typhoon" in Region 1 corresponds to Japanese "taifu," which is a broader category than "typhoon."

Region	Wind Speed (knots)
Region	-17	17-28	28-34	34-48	48-64	64-90	90-116	116-120
1	Low pressure area	Tropical depression		Tropical storm	Severe tropical storm	Typhoon
2	Tropical disturbance	Tropical depression		Tropical storm		Hurricane
3	Low pressure area	Depression	Deep depression	Cyclonic storm	Severe cyclonic storm	Very severe cyclonic storm		Super cyclonic storm
4	Tropical disturbance		Tropical depression	Moderate tropical storm	Severe tropical storm	Tropical cyclone	Intense tropical cyclone	Very intense tropical cyclone
5	Tropical disturbance	Tropical depression		Tropical cyclone		Tropical cyclone (hurricane), Severe tropical cyclone

Number	Region
1	Western North Pacific Ocean and South China Sea
2	Atlantic and Northeast Pacific Oceans including Caribbean and Gulf of Mexico
3	North Indian Ocean including Bay of Bengal and Arabian Sea
4	Southwest Indian Ocean
5	South Pacific Ocean and Southeast Indian Ocean

2. Different Direction of Rotation

In terms of a large cyclone (a tropical cyclone and an extratropical cyclone), the rotation near the ground is always anti-clockwise in the northern hemisphere, while clockwise in the southern hemisphere. The air moving into the center near the ground moves out of the center in the upper troposphere, rotating in the opposite direction to that near the ground, namely, clockwise in the northern hemisphere, and anti-clockwise in the southern hemisphere. In these cases, Coriolis effect determines the rotation of vortices.

The rotation of a small cyclone such as a tornado (and a willy-willy), on the other hand, is little influenced by Coriolis effect in comparison to other forces such as centrifugal force, so the rotation may be either clockwise or anti-clockwise. From the result of a survey, however, that the rotation of small cyclones that is more often than not in the same direction with large cyclones.

By the way, for even more small vortices, like the flow of water going down the drain, the Coriolis force has a even weaker impact in comparison to other forces. It is therefore a very rare case that the Coriolis force is the most major factor to explain the direction of rotation in the Northern and Southern hemisphere. When the direction appears to be opposite, it is likely to be a coincidence.

3. Link Collection

The following is a link collection on tropical cyclones in the world. The latest tropical cyclone information in the world is summarized in other pages such as Weather Information or Typhoon Information (JMA and JTWC).

Digital Typhoon: Typhoons, Hurricanes and Cyclones

1. Typhoons, Hurricanes and Tropical Cyclones in the World

2. Different Direction of Rotation

3. Link Collection