You are here Tropical cyclones/storms Classification and Warning System

Zone of disturbed weather (or tropical disturbance):
An area of low pressure relative to the surrounding region; the associated cloud
masses are usually not well-organized.

Tropical depression:
A non-frontal synoptic scale low-pressure system originating over tropical waters with enhanced convection and/or some indications of cyclonic wind circulation. Winds circulate clockwise around low-pressure and cyclone systems in the southern hemisphere. Gusts associated with tropical depression are generally less than 89 kilometres (km) per hour.

Moderate tropical storm:
A non-frontal synoptic scale low-pressure system originating over tropical waters with organized convection and definite cyclonic wind circulation. Estimated gusts associated with moderate tropical storms range from 89 to 124 km per hour.

Severe tropical storm:
A tropical storm in which the estimated wind gusts range from 125 to 165 km per hour.

Tropical cyclone:
A tropical storm in which the estimated wind gusts range from 166 to 233 km per hour.

Intense tropical cyclone:
A tropical storm in which the estimated wind gusts range from 234 to 299 km per hour.

Very intense tropical cyclone:
A tropical storm in which estimated gusts exceed 300 km per hour.
 

THE CYCLONE WARNING SYSTEM (MAURITIUS AND RODRIGUES)

Class I
Issued 36 to 48 hours before the advent of cyclonic conditions.

Class II:
Issued so as to allow, as far as practicable, 12 hours of daylight before the occurrence of gusts of 120 kilometers (km) per hour.

Class III:
Issued so as to allow, as far as practicable, 6 hours of daylight before the occurrence of gusts of 120 kilometers(km) per hour.

Class IV:
Issued when gusts of 120 km per hour have been recorded and are expected to continue to occur.

Termination: Issued when there is no longer any appreciable danger of gusts exceeding 120 km per hour.

The system of naming tropical cyclones was introduced in 1960, which will be remembered as the year during which Mauritius was struck by cyclone "Alix" and by cyclone "Carol", the most devastating cyclone on record.

Madagascar, Reunion, Seychelles, Comores, and Mauritius use a common list of names for identifying tropical depressions. Mauritius is responsible for naming depressions forming in the region lying between longitude 55ºE and 90ºE. Madagascar is responsible for the region west of longitude 55ºE and the Australian Bureau of Meteorology for the region east of 90ºE. Whenever a cyclone moves from the Australian region of responsibility to that of Mauritius, it is given a hyphenated name comprising the names from both regions for a period of about 24 hours. Thereafter it is known by the South West Indian Ocean name.