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Classification of Tropical Cyclones by Strength

The following table lists the tropical cyclone categories used by various meteorological agencies:

Wind Speed (km/h)
Beaufort Scale
Central Pressure*
(hPa)
Classification
JMA
(10-min average)
HKO
(10-min average)
CMA
(2-min average)
CWB
(10-min average)
JTWC
(1-min average)
NHC
(1-min average)
<41
<6
---
Tropical Depression
Low Pressure Area
---
Tropical Depression
Tropical Disturbance
Tropical Disturbance
41-62
6-7
1000
Tropical Depression
Tropical Depression
Tropical Depression
Tropical Depression
63-87
8-9
990-999
Tropical Storm
Tropical Storm
Tropical Storm
Tropical Storm
Tropical Storm
Tropical Storm
88-117
10-11
980-989
Severe Tropical Storm
Severe Tropical Storm
Severe Tropical Storm
Severe Tropical Storm
118-153
12
960-979
Typhoon
Typhoon (up to 149 km/h)
Typhoon (up to 149 km/h)
Typhoon (up to 183 km/h)
Typhoon
Hurricane Category 1
154-177
945-959
Severe Typhoon
(150 to 184 km/h)
Severe Typhoon
(150 to 183 km/h)
Hurricane Category 2
178-209
930-944
Super Typhoon
(from 185 km/h)
Super Typhoon
(from 184 km/h)

Severe Typhoon
(from 184 km/h)

Major Hurricane Category 3
210-240
915-929
Major Hurricane Category 4
241-249
905-914
Super Typhoon
>250
<905
Major Hurricane Category 5

* Central Pressure refers to NW Pacific standard.

Dvorak T-Number

Dvorak technique is a method developed by meteorologist Vernon Dvorak to estimate the intensity of tropical cyclones based on satellite imageries. A T-Number is given to a tropical cyclone after analysis which is used to approximate its strength in terms of wind speed and pressure.

T-Number
Wind speed
Central Pressure in NW Pacific (hPa)
Classification (HKO, NHC & JTWC mixed)
Example (all examples except those for T7.5 are taken from the 2005 or 2006 seasons)
1.0
<46 km/h, <25 kt
---
Low Pressure Area
(Most storms with at most T1.5 are not given names because they do not meet the criteria of a tropical storm, and are thus not upgraded by the JMA).
1.5
Tropical Depression
2.0
55 km/h, 30 kt
1000
Tropical Depression
TD Trami
2.5
65 km/h, 35 kt
997
Tropical Storm
TS Rumbia
3.0
83 km/h, 45 kt
991
Tropical Storm
TS Jelavat
3.5
102 km/h, 55 kt
984
Severe Tropical Storm
STS Bilis
4.0
120 km/h, 65 kt
976
Typhoon Cat. 1
TY Maria
4.5
143 km/h, 75 kt
966
Typhoon Cat. 1
TY Bolaven
5.0
167 km/h, 90 kt
954
Typhoon Cat. 2
TY Kaemi
5.5
189 km/h, 102 kt
941
Typhoon Cat. 3
TY Utor
6.0
213 km/h, 115 kt
927
Typhoon Cat. 4
TY Khanun
6.5
235 km/h, 127 kt
914
Typhoon Cat. 4
TY Chebi, Durian, Xangsane, Chanchu
7.0
259 km/h, 140 kt
898
Super Typhoon Cat. 5
TY Saomai, Ioke, Yagi, Cimaron
7.5
287 km/h, 155 kt
879
Super Typhoon Cat. 5
TY Ivan (1997), Joan (1997), Zeb (1998), Dianmu (2004), Chaba (2004)
8.0
315 km/h, 170 kt
858
Super Typhoon Cat. 5
(No TCs of T-Number 8.0 have ever formed)

Classification of Tropical Cyclones by Size

Tropical cyclones can also be classified according to its size. A list is given as follows.

Size Radius in Degrees Latitude Radius in Conventional Units
Midget / Very small (迷你) < 2 < 220 km / 120 nm
Small (小型) 2 - 3 220 - 335 km / 120 - 180 nm
Average / Medium (中型) 3 - 6 335 - 665 km / 180 - 360 nm
Large (大型) 6 - 8 665 - 890 km / 360 - 480 nm
Very large (特大) > 8 > 890 km / > 480 nm

Last Accessed: Thu May 25 2017 01:47:41 HKT
Last Modified: Tue Dec 24 2013

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