Monday, July 15, 2013

STH Stormwatch (15Jul2013) - Reporting a low pressure area in the Bay of Bengal



How are low pressure systems classified in India? What are the differences between low, depression and cyclone?

A low pressure system over Indian region is classified based on the maximum sustained winds speed associated with the system and the pressure deficit/ number of closed isobars associated with the system. The pressure criteria is used, when the system is over land and wind criteria is used, when the system is over the sea. The system is called as low if there is one closed isobar in the interval of 2 hPa. It is called depression, if there are two closed isobars, a deep depression, if there are three closed isobars and cyclonic storm if there are four or more closed isobars.
Considering wind criteria, the system with wind speed of 31 -50 kmph is called as depression and the low pressure system with maximum sustained 3 minutes surface winds between 51–59 kmph is called a deep depression. The system with maximum sustained 3 minutes surface winds of 63 knots or more is called as cyclonic storm
System
Associated wind speed
Kmph
Low pressure area
32
Depression
32–50
Deep Depression
51–59
Cyclonic Storm
60-90
Severe Cyclonic Storm (SCS)
90-119
Very Severe Cyclonic Storm
119-220
Super Cyclonic Storm
Excess of 220
Source

Praful Rao,
Kalimpong,
Dist Darjeeling

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