Indian Geography15 Concepts & Facts

Tropical Cyclones: IMD Naming & Regional Tracks Questions

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Tropical cyclones in the North Indian Ocean basin are intense low-pressure synoptic systems characterized by closed cyclonic wind circulations fueled by the release of latent heat of condensation. Cyclogenesis requires specific thermodynamic and kinematic thresholds: sea surface temperatures (SST) exceeding 27°C, substantial upper-ocean thermal energy, adequate Coriolis acceleration at least 5° away from the equator, high middle-tropospheric humidity, weak vertical wind shear between the lower and upper troposphere, and a pre-existing cyclonic vorticity perturbation. The basin exhibits a bimodal seasonal frequency, peaking during the pre-monsoon months of April to May and the post-monsoon transitional window of October to December, when atmospheric conditions become conducive to rapid convective intensification.

A pronounced climatological disparity exists between the Bay of Bengal and the Arabian Sea, with the former experiencing roughly four times more cyclones. This asymmetry stems from the Bay of Bengal's semi-enclosed concave geometry, higher sea surface temperatures, and massive freshwater discharge from perennial rivers like the Ganga and Brahmaputra, which stratifies the surface layer and inhibits vertical ocean mixing. Remnant low-pressure depressions from the South China Sea also enter the basin, undergoing re-intensification. The India Meteorological Department (IMD) classifies these disturbances by maximum sustained surface wind speeds, ranging from Depression (31–49 km/h) and Deep Depression (50–61 km/h) to Cyclonic Storm (62–88 km/h), Severe Cyclonic Storm, Extremely Severe Cyclonic Storm, and Super Cyclonic Storm exceeding 222 km/h. Coastal landfalls are frequently compounded by destructive storm surges driven by bathymetric shoaling.

Institutional monitoring is directed by the IMD through the Regional Specialized Meteorological Centre (RSMC) New Delhi, designated by the World Meteorological Organization (WMO) to issue regional advisories. Following the 2018 expansion of the WMO/ESCAP Panel on Tropical Cyclones to 13 member states, an updated 169-name roster was instituted in April 2020, incorporating Indian submissions such as Gati, Tej, and Jaladhi that are retired permanently once used. Disaster response is coordinated by the National Disaster Management Authority (NDMA) through Doppler weather radar networks, four-stage color-coded warnings, and cyclone shelters. In UPSC CSE and SSC CGL examinations, key topics include cyclogenesis thermodynamic criteria, the structure of the cyclone eye and eyewall, IMD warning stages, and regional coastal hazard mitigation policies.

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RSMC New Delhi, operated by the India Meteorological Department (IMD), is one of six global Regional Specialized Meteorological Centres designated by the WMO to track tropical cyclones.

The WMO/ESCAP Panel on Tropical Cyclones expanded its membership in 2018 from 8 to 13 nations: Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, UAE, and Yemen.

The April 2020 cyclone naming table comprises 169 names, with each of the 13 member nations submitting 13 names arranged in an alphabetical matrix used sequentially.

Names proposed by India in the 2020 WMO/ESCAP matrix include Gati, Tej, Murasu, Aag, Vyom, Jhar, Probaho, Neer, Prabhanjan, Ghurni, Ambud, Jaladhi, and Vega.

Cyclone names in the North Indian Ocean are never reused; once a named tropical cyclone concludes its lifecycle, the assigned moniker is retired permanently.

The Bay of Bengal experiences two distinct cyclonic peaks annually: a pre-monsoon peak during April–May and a significantly more intense post-monsoon peak during October–December.

Recurvature of Bay of Bengal cyclones occurs when westward-moving storms encounter the western periphery of the subtropical ridge, steering them northward and northeastward toward Odisha and Bangladesh.

The shallow bathymetry and triangular funnel shape of the northern Bay of Bengal make the Sundarbans and Odisha coasts exceptionally vulnerable to amplified storm surges.

Storm surge height is governed by the inverse barometer effect, where every 1 hectopascal (hPa) drop in central atmospheric pressure produces an approximate 1-centimetre rise in ocean water level.

#10

The 1970 Bhola Cyclone remains the deadliest tropical cyclone on human record, generating a 10-metre storm surge in the Bay of Bengal that killed over 300,000 people.

#11

Stage 1 of IMD's cyclone warning system, the 'Pre-Cyclone Watch', is issued at least 72 hours in advance to alert maritime authorities and state disaster response forces.

#12

Stage 2, designated 'Cyclone Alert' (coded Orange), is issued 48 hours prior to expected coastal landfall, detailing storm track, wind velocity, and expected precipitation.

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Stage 3, designated 'Cyclone Warning' (coded Red), is issued 24 hours before landfall, specifying target district impacts and mandating evacuation of low-lying coastal populations.

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Stage 4, the 'Post-Landfall Outlook', is issued 12 hours prior to landfall to warn interior districts of gale-force squalls, riverine flash floods, and infrastructure disruption.

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IMD deploys a coastal network of Doppler Weather Radars (DWR) operating on S-band and C-band frequencies to track cyclone landfall positions within a 400-kilometre range.

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Tropical cyclones are intense low-pressure systems formed over warm tropical waters, bringing gale-force winds, torrential downpours, and destructive storm surges. In the North Indian Ocean, cyclonic activity peaks twice a year: during pre-monsoon months (April–May) and the more severe post-monsoon window (October–December). The India Meteorological Department monitors these storms using coastal Doppler radars. Cyclones are named sequentially from a predefined list contributed by thirteen regional nations under the World Meteorological Organization, ensuring clear public disaster communications.

Geography and disaster management questions in UPSC and SSC exams regularly test cyclone dynamics and the India Meteorological Department warning protocol. A common exam trap mixes up the four warning stages and their lead times: remember that Stage 1 (Pre-Cyclone Watch) is issued 72 hours before landfall, Stage 2 (Cyclone Alert, Orange) 48 hours prior, and Stage 3 (Cyclone Warning, Red) 24 hours prior. In prelims, remember that once an Indian Ocean cyclone name is used, it is retired permanently.

Tropical Cyclones: IMD Naming & Regional Tracks Questions

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