A tropical cyclone is a massive, rotating storm system characterized by a low-pressure center, strong winds, and heavy rainfall. These storms form over warm tropical or subtropical waters. These powerful weather phenomena are known by various names globally, depending on the ocean basin where the storm originates.
The Primary Terminology for Indian Ocean Storms
The term used for these rotating storm systems throughout the Indian Ocean is “Tropical Cyclone.” While this is the overarching scientific classification, the term is often shortened to “Cyclone” in common usage within the region. The North Indian Ocean, including the Bay of Bengal and the Arabian Sea, classifies these systems based on the maximum sustained wind speed averaged over a three-minute period.
A tropical system must reach a maximum sustained wind speed of at least 34 knots (62 kilometers per hour) to be officially designated as a Cyclonic Storm and assigned a name. Below this threshold, the storm is classified as a Depression or a Deep Depression. As a storm strengthens, the India Meteorological Department (IMD) uses a seven-level scale. This scale includes stages such as Severe Cyclonic Storm and Very Severe Cyclonic Storm (118 to 167 km/h). The highest classification is a Super Cyclonic Storm, reserved for systems with winds of 222 kilometers per hour or higher.
Regional Monitoring and Naming Conventions
The Indian Ocean basin is divided into geographical areas monitored by two distinct Regional Specialized Meteorological Centers (RSMCs). The North Indian Ocean, covering the Arabian Sea and the Bay of Bengal, falls under the responsibility of the RSMC in New Delhi, operated by the India Meteorological Department. This center provides advisories and storm surge warnings to 13 member countries within the region.
The naming system for the North Indian Ocean is managed collaboratively by the World Meteorological Organization (WMO) and the ESCAP Panel on Tropical Cyclones. Member countries contribute names to a sequential list that ensures names are not repeated once used. This convention began in 2004 to help the public and disaster managers quickly identify and track individual storms.
The Southwest Indian Ocean, extending from the east coast of Africa to 90 degrees East longitude, is monitored by RSMC La Réunion. This center, run by Météo-France, maintains naming lists and issues advisories for its area. Although both regions use the general term “Tropical Cyclone,” the specific naming protocols and intensity scales are maintained separately by the two RSMCs.
Comparing Global Tropical Cyclone Terms
The meteorological phenomenon is essentially the same worldwide, but the name used reflects the storm’s geographical origin. Storms in the Atlantic Ocean and the Northeast Pacific Ocean are referred to as “Hurricanes.” Those that form in the Northwest Pacific Ocean are known as “Typhoons.” All three terms—Hurricane, Typhoon, and Cyclone—describe a mature tropical cyclone.
The different names are tied to historical, cultural, and geographical conventions of the respective ocean basins. The intensity scales used in the Indian Ocean differ from the Saffir-Simpson Hurricane Wind Scale used for Atlantic hurricanes. The Saffir-Simpson scale uses a five-category system based on one-minute sustained wind speeds. In contrast, the Indian Ocean’s classification uses a more granular multi-stage system, such as Very Severe Cyclonic Storm, specific to the region’s operational needs.