Cyclones: Formation of Tropical Cyclones, Structure, Classification, Naming, Temperate Cyclones and Cyclone Management in India (UPSC Notes + PYQs)

Conditions for a tropical cyclone

• Large sea surface with temperature above about 26.5-27°C, to a depth of around 50 m.
• Coriolis force strong enough to start rotation, so cyclones rarely form within about 5° of the equator.
• Low vertical wind shear, so the storm can grow tall.
• A pre-existing weak low-pressure area or disturbance.
• Upper-level divergence that removes rising air.
• Moist mid-troposphere.

The South Atlantic and South-East Pacific rarely see tropical cyclones because their seas are cooler, as cold currents (Benguela, Humboldt) flow there, and wind shear is high. Mains 2024 asked how rising sea surface temperature affects cyclones: warmer seas give more energy, faster intensification and heavier rain.

Structure

At the centre is the eye, 20-50 km across: calm, mostly clear, with the lowest pressure and air that sinks and warms, so the eye is warmer than its surroundings. Around it is the eyewall, a ring of tall clouds with the strongest winds and heaviest rain. Outer rain bands spiral inwards. Not every cyclone develops a clear eye; it forms when the storm is well organised.

IMD classification (North Indian Ocean)

A storm gets a name once it reaches cyclonic storm level.

Naming

The WMO/ESCAP Panel on Tropical Cyclones names storms in the North Indian Ocean. Its 13 members (Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, UAE, Yemen) contributed 13 names each to a list of 169 adopted in 2020. The IMD’s Regional Specialised Meteorological Centre in New Delhi assigns names in turn. Names are not reused. Elsewhere tropical cyclones are called hurricanes (Atlantic, East Pacific) and typhoons (North-West Pacific).

Temperate (extra-tropical) cyclones

These form in mid-latitudes (35°-65°) where cold polar air meets warm tropical air along a front (polar front theory of Bjerknes). They are larger, cover land and sea, move west to east with the westerlies, have no eye, and bring widespread, steady rain. Western disturbances, which give winter rain and snow to north-west India, are related low-pressure systems from the Mediterranean region.

Bay of Bengal vs Arabian Sea

The Bay of Bengal gets several times more cyclones than the Arabian Sea: it is warmer, receives remnants of Pacific typhoons, has low salinity surface water that keeps heat near the surface, and its funnel shape and flat deltaic coast make storm surges deadly. But the Arabian Sea has warmed fast, and strong cyclones there (Tauktae 2021, Biparjoy 2023) have become more common. Peak seasons: May and October-December, around monsoon onset and withdrawal.

Impact and management in India

About 5,700 km of India’s 7,500 km coastline is exposed to cyclones and tsunamis. The deadliest threat is the storm surge, followed by flooding rain and wind. The 1999 Odisha super cyclone killed about 10,000 people; after early warning, shelters and drills, Phailin (2013) and Fani (2019) saw far fewer deaths though they were similar in strength. Tools: IMD’s warnings, Doppler radars, NCRMP (shelters, embankments, warning systems with World Bank support), mangrove belts (which reduced damage in parts of Odisha in 1999), coastal regulation, and the “zero casualty” approach of Odisha.

Why India now loses fewer lives

The Odisha super cyclone of 1999 killed nearly 10,000 people. When Cyclone Phailin struck the same coast in 2013, fewer than 50 died, and Fani (2019) caused a similar low toll despite its strength. The change came from better forecasts and better planning. IMD’s track forecasts are now accurate to within about 100 km three days ahead, helped by Doppler weather radars along the coast and satellites such as INSAT-3D. Odisha built hundreds of multipurpose cyclone shelters, trained local volunteers, and moved over a million people before Phailin. The National Cyclone Risk Mitigation Project, supported by the World Bank, funded shelters, evacuation roads, saline embankments and early warning systems in coastal States. The UN praised Odisha’s “zero casualty” approach as a model.

Climate change and Arabian Sea cyclones

The Arabian Sea has warmed faster than most oceans, and studies by IITM Pune and others link this to a rise in the number and duration of severe cyclones there since 2000. Tauktae (2021) and Biparjoy (2023) were among the strongest in recent memory on the west coast. Cyclones are also intensifying rapidly, jumping categories within a day, which shortens warning time. Coastal cities such as Mumbai, Surat and Kochi, long thought to be relatively safe, now need the shelter and warning systems the east coast has built. Mangroves, as the Sundarbans showed during Amphan (2020), reduce storm surge and must be protected.

PYQ trend

Prelims asked the eye and jet streams (2020) and why cyclones don’t form in the South Atlantic (2015). Mains asked sea surface temperature and cyclones (2024) and the Fujiwhara effect (2026), the interaction of two nearby cyclones that rotate around each other and may merge.

Cyclones: UPSC angle

Cyclones UPSC PYQs (Prelims)

Questions UPSC has actually asked, from the official papers. Pick an option to check yourself.

Mains PYQs on this topic

Questions from the official UPSC Mains papers (2023-2026 in the Battle IAS Mains bank), newest first. Each links to a model answer.

1. UPSC Mains 2026 · GS Paper I · Q4 · 10 marks

   What is the Fujiwhara effect? Explain its impact on the movement and intensity of tropical cyclones.

   Model answer and approach

2. UPSC Mains 2024 · GS Paper I · Q4 · 10 marks

   What is sea surface temperature rise? How does it affect the formation of tropical cyclones?

   Model answer and approach

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