Tropical Cyclone Scales - North Indian Ocean

North Indian Ocean

Any tropical cyclone that develops within the Northern Hemisphere between 100°E and 45°E in the Northern Hemisphere, is monitored by the India Meteorological Department's Regional Specialized Meteorological Center in New Delhi, India. Other warning centres such as RSMC La Reunion, the Bangladesh Meteorological Department and the United States Joint Typhoon Warning Center, also monitor tropical cyclones developing within the basin. RSMC New Delhi uses a 3-minute averaging period to determine the sustained windspeeds of a tropical cyclone.

Official classifications

The lowest category used by RSMC New Delhi, is a depression which have 3-minute sustained windspeeds of under 27 kn (31 mph; 50 km/h), while a deep depression has windspeeds of between 27 kn (31 mph; 50 km/h) and 33 kn (38 mph; 61 km/h). Should a deep depression further intensify, it will be classified as a Cyclonic Storm and assigned a name should it develop sustained windspeeds of between 34 kn (39 mph; 63 km/h) and 48 kn (55 mph; 89 km/h).

In cases where cyclonic storms possess wind speeds greater than 48 kt, (88 km/h, 55 mph), they are classified as severe cyclonic storms. A severe cyclonic storm is labelled as a very severe cyclonic storm when it reaches wind speeds greater than 64 kt, (118 km/h, 74 mph). A Super Cyclonic Storm is the highest category used to designate tropical cyclones and have 3-minute sustained windspeeds of above 120 kn (140 mph; 220 km/h)

Prior to 1988, cyclones were classified into 4 categories, which were depression, deep depression, cyclonic storms(34-47 knots) and severe cyclonic storms(48 knots or more). However in 1988 the IMD started to rate cyclones with wind speeds of more than 64 kt, (118 km/h, 74 mph) as very severe cyclonic storms. The IMD then made another change in 1998 to introduce a category for super cyclonic storms, which are cyclonic storms with wind speeds of more than 120 kt, (222 km/h, 138 mph)