Tropical Cyclones
GS Paper I | Geography | Physical Geography | Climatology | Tropical Cyclones | Prelims + Mains
Study Material
Tropical cyclones are among the most powerful weather systems on Earth. But for UPSC, this chapter is not simply about learning what a cyclone is.
The questions show a much deeper pattern.
UPSC has asked why cyclones form only in particular oceanic regions, why they are rare in some tropical seas, how rising sea-surface temperature affects them, how warnings are communicated, and most recently, how two tropical cyclones can interact through the Fujiwhara Effect.
So the right preparation strategy is:
Formation → Structure → Distribution → Indian Ocean Pattern → Hazards → Forecasting → Climate Change → Fujiwhara Effect
What UPSC PYQs Tell Us
The previous questions give us a clear roadmap.
| Year | Stage | What UPSC Tested |
|---|---|---|
| 2014 | Mains GS-I | Why tropical cyclones are concentrated in selected ocean basins |
| 2015 | Prelims | Why tropical cyclones rarely originate in South Atlantic and south-eastern Pacific |
| 2022 | Mains GS-I | IMD's colour-coded cyclone/weather warnings |
| 2024 | Mains GS-I | Sea-surface temperature rise and cyclone formation |
| 2026 | Mains GS-I | Fujiwhara Effect and its influence on cyclone movement and intensity |
The pattern is unmistakable.
UPSC wants students to understand five things:
- Conditions necessary for cyclogenesis
- Why cyclone distribution is uneven
- Ocean-atmosphere interaction
- Cyclone hazards and disaster preparedness
- New atmospheric phenomena linked with cyclones
That is why these notes give more weight to these areas.
What Is a Tropical Cyclone?
A tropical cyclone is an intense rotating low-pressure weather system that develops over warm tropical or subtropical oceans.
It consists of:
- strong spiralling winds,
- deep convective clouds,
- very heavy rainfall,
- a low-pressure centre,
- and, in a mature storm, an eye and eyewall.
IMD treats a tropical low-pressure system as a Cyclonic Storm when its maximum sustained surface wind reaches at least 34 knots, or about 62 km/h.
The same broad phenomenon has different regional names:
North Atlantic and eastern North Pacific → Hurricane
North-western Pacific → Typhoon
North Indian Ocean and South Indian Ocean → Cyclone
These are not fundamentally different weather systems.
They are regional names for tropical cyclones.
Tropical Cyclone vs Temperate Cyclone
Do not mix the two.
| Tropical Cyclone | Temperate Cyclone |
|---|---|
| Develops mainly over warm tropical oceans | Develops mainly in middle latitudes |
| Warm-core system | Usually cold-core or frontal system |
| No fronts | Associated with warm and cold fronts |
| Energy mainly from latent heat released by condensation | Energy mainly from horizontal temperature contrasts |
| Nearly circular and compact | Usually larger and more asymmetric |
| Eye may develop | Distinct eye usually absent |
| Strongest winds close to eyewall | Winds distributed over a broader region |
Prelims trap
A tropical cyclone is not a frontal cyclone.
The presence of well-developed warm and cold fronts points towards an extratropical or temperate cyclone.
Conditions Necessary for Tropical Cyclone Formation
This is the most important part of the chapter.
A warm sea alone does not automatically produce a cyclone.
Several conditions must occur together.
1. Warm Ocean Water
Tropical cyclones need sufficiently warm water to provide energy.
IMD identifies ocean temperatures of roughly 26.5°C or above, extending through a sufficient depth—of the order of about 50 metres—as an important requirement.
Why does depth matter?
Suppose only a very thin surface layer is warm.
Strong cyclone winds can churn the ocean and bring colder water upward.
The surface then cools quickly and the cyclone loses energy.
A deeper layer of warm water provides a much larger energy reservoir.
This becomes particularly important when discussing:
- Ocean Heat Content,
- rapid intensification,
- climate change.
2. Sufficient Coriolis Force
Air moving towards the low-pressure centre must begin rotating.
That rotation is supported by the Coriolis force.
Coriolis force is practically zero at the Equator and strengthens with latitude.
Therefore tropical cyclones rarely form very close to the Equator.
They generally require some distance from it.
Key idea
Warmest water may occur near the Equator, but cyclones do not normally originate exactly there because rotation is too weak.
This is a favourite conceptual trap.
3. Pre-existing Low-Pressure Disturbance
Cyclones usually do not appear suddenly from an undisturbed atmosphere.
An initial disturbance is generally required.
This may be:
- a low-pressure area,
- tropical wave,
- monsoon disturbance,
- remnant circulation of another system.
It provides the initial convergence and rotation around which organised convection can develop.
4. High Atmospheric Moisture
Warm ocean water causes strong evaporation.
The lower and middle atmosphere must contain sufficient moisture.
Moist air rises and cools.
Water vapour condenses.
Condensation releases latent heat.
That latent heat is the main energy source sustaining the cyclone.
5. Atmospheric Instability
The atmosphere must allow warm moist air near the surface to rise strongly.
If the atmosphere is unstable:
warm moist air rises → thunderstorms grow → latent heat is released → pressure falls further
This helps create a positive feedback mechanism.
6. Low Vertical Wind Shear
Vertical wind shear means a change in wind speed or direction with height.
Strong vertical wind shear can tilt or tear apart the developing cyclone.
For a strong, vertically organised tropical cyclone, wind shear should generally be relatively weak.
This explains an important Indian Ocean feature.
During the southwest monsoon, strong low-level westerlies and upper-level easterlies create substantial vertical wind shear.
IMD notes that this is one reason intense tropical cyclones are comparatively uncommon during the peak southwest monsoon months.
7. Upper-Level Outflow
Air entering near the ocean surface rises inside the storm.
For the pressure at the surface to continue falling, that air must be able to escape efficiently at higher levels.
A good upper-level outflow acts almost like an exhaust system.
Without it, rising air would accumulate above the cyclone and suppress further intensification.
Formation of a Tropical Cyclone: The Heat-Engine Explanation
The easiest way to understand a tropical cyclone is to imagine a heat engine.
IMD itself describes tropical cyclones in this way.
Step 1
Warm ocean water causes strong evaporation.
↓
Step 2
Warm, moist air rises.
↓
Step 3
Surface pressure falls.
↓
Step 4
Surrounding air moves towards the low-pressure centre.
↓
Step 5
Coriolis force causes the inflowing air to rotate.
↓
Step 6
Rising moisture condenses into clouds and rain.
↓
Step 7
Condensation releases latent heat.
↓
Step 8
The air becomes warmer and more buoyant, encouraging further uplift.
↓
Step 9
Surface pressure falls further and winds strengthen.
↓
Step 10
If warm water, moisture and favourable winds persist, the system intensifies.
So the cyclone feeds itself through:
Warm Ocean → Evaporation → Condensation → Latent Heat → Stronger Convection → Lower Pressure → Stronger Winds
Why Does a Cyclone Rotate?
Surface air moves towards the low-pressure centre.
But because Earth is rotating, the Coriolis force deflects the moving air.
Therefore:
Northern Hemisphere → counter-clockwise circulation
Southern Hemisphere → clockwise circulation
IMD confirms this hemispheric reversal.
Important trap
This does not mean ordinary water draining from a sink must rotate in a fixed direction depending on hemisphere.
The Coriolis effect is important for large atmospheric systems, not everyday household drains.
Structure of a Mature Tropical Cyclone
A mature cyclone is highly organised.
Its main components are:
Eye → Eyewall → Spiral Rainbands → Upper-Level Outflow
The Eye
At the centre lies the eye.
It is characterised by:
- very low atmospheric pressure,
- relatively calm winds,
- descending air,
- sometimes clearer skies.
This seems strange.
How can the centre of a violent storm be relatively calm?
Because the strongest rising motion is concentrated around the eye rather than within it.
Eyewall
The eye is surrounded by the eyewall.
This is usually the most dangerous part of a mature tropical cyclone.
It contains:
- strongest winds,
- intense convection,
- towering cumulonimbus clouds,
- extremely heavy rainfall.
Prelims trap
Strongest winds are not inside the eye.
They usually occur in the eyewall.
Spiral Rainbands
Bands of thunderstorms spiral towards the cyclone centre.
They can extend hundreds of kilometres away.
Even places far from the eye may therefore experience:
- heavy rain,
- strong gusts,
- flooding,
- tornado-like local disturbances.
Upper-Level Outflow
Air rises strongly in the eyewall and then spreads outward at high altitude.
This outflow helps evacuate air from the cyclone column and supports low pressure near the surface.
Why Is the Eye Warm?
A tropical cyclone is a warm-core system.
Air in the centre descends.
As it descends, it compresses and warms.
This contributes to the relatively warm conditions in the eye compared with the surrounding storm.
Warm-core structure is one of the major differences between tropical and extratropical cyclones.
Life Cycle of a Tropical Cyclone
A simplified sequence over the North Indian Ocean is:
Low-Pressure Area
↓
Depression
↓
Deep Depression
↓
Cyclonic Storm
↓
Severe Cyclonic Storm
↓
Very Severe / Extremely Severe Cyclonic Storm
↓
Super Cyclonic Storm
Not every disturbance reaches the final stages.
Many weaken before becoming a cyclonic storm.
IMD Classification of Cyclonic Systems
For the North Indian Ocean, IMD uses maximum sustained wind speed to classify systems over the sea.
| System | Maximum Sustained Wind |
|---|---|
| Depression | 31–49 km/h |
| Deep Depression | 50–61 km/h |
| Cyclonic Storm | 62–88 km/h |
| Severe Cyclonic Storm | 89–117 km/h |
| Very Severe Cyclonic Storm | 118–166 km/h |
| Extremely Severe Cyclonic Storm | 167–221 km/h |
| Super Cyclonic Storm | ≥222 km/h |
Prelims point
Do not apply the Saffir-Simpson hurricane categories mechanically to IMD classifications.
Different agencies may also use different wind-averaging periods.
IMD uses a 3-minute sustained wind measure in its North Indian Ocean operational system.
What Is Landfall?
A cyclone makes landfall when the centre of the tropical cyclone crosses the coastline.
For a mature cyclone with an eye, landfall occurs when the eye centre crosses the coast.
Important distinction
Landfall ≠ first rain from the cyclone
Outer rainbands can reach land many hours before the cyclone centre crosses the coast.
Why Does a Cyclone Weaken after Landfall?
A cyclone depends on warm ocean water for energy and moisture.
After entering land:
- oceanic heat supply is cut off,
- moisture supply decreases,
- surface friction increases,
- terrain disrupts circulation.
The cyclone therefore normally weakens.
But this does not mean the danger ends immediately.
Remnants can still cause:
- torrential rainfall,
- river floods,
- landslides,
- urban flooding.
Where Do Tropical Cyclones Occur?
Major tropical cyclone basins include:
- North Atlantic,
- eastern North Pacific,
- western North Pacific,
- North Indian Ocean,
- South Indian Ocean,
- Australian and South Pacific region.
But their frequency is very uneven.
This geographical unevenness has repeatedly interested UPSC.
Why Are Tropical Cyclones Rare near the Equator?
This is mainly because the Coriolis force becomes too weak close to the Equator.
Without sufficient Coriolis force, the required large-scale rotation cannot organise effectively.
So:
Warm water alone is not enough.
That single sentence can eliminate many Prelims options.
Why Are Tropical Cyclones Rare in the South Atlantic and South-Eastern Pacific?
UPSC Prelims tested this directly.
The South Atlantic and south-eastern tropical Pacific generally lack the combination of conditions that routinely creates tropical cyclones.
One important feature is that the ITCZ and associated tropical disturbances are much less favourable there, while cooler waters and atmospheric conditions can further suppress cyclogenesis.
The broader lesson is:
A cyclone requires several factors simultaneously.
Warm water alone cannot explain global cyclone distribution.
Why Are Certain Seas Highly Cyclone-Prone?
UPSC Mains 2014 asked why tropical cyclones are particularly associated with regions such as:
- South China Sea,
- Bay of Bengal,
- Gulf of Mexico.
These areas commonly provide a favourable combination of:
- warm tropical waters,
- adequate Coriolis force,
- moisture,
- atmospheric instability,
- pre-existing disturbances,
- suitable wind-shear conditions.
Therefore the geographical distribution of cyclones reflects the overlap of oceanic + atmospheric conditions.
Tropical Cyclones over the North Indian Ocean
For India, two basins matter:
Bay of Bengal
Arabian Sea
Both produce cyclones.
But historically the Bay of Bengal has produced more.
Why Does the Bay of Bengal Get More Cyclones than the Arabian Sea?
This is a high-value India-specific concept.
IMD identifies several reasons.
First, some disturbances develop directly over the south-eastern Bay of Bengal and adjoining Andaman Sea.
Second, remnants of western Pacific typhoons can move through the South China Sea and contribute disturbances to the Bay of Bengal.
Third, the Arabian Sea has historically been relatively cooler than the Bay of Bengal, making cyclone formation and intensification less favourable.
Many Bay cyclones also weaken after crossing the Indian peninsula, so relatively few survive to migrate into the Arabian Sea.
Prelims summary
Bay of Bengal > Arabian Sea cyclone frequency
But never conclude:
“Arabian Sea cannot produce intense cyclones.”
It can.
Why Are Cyclones Less Common during Peak Southwest Monsoon?
This looks surprising.
The ocean is warm and moisture is abundant.
So why are July–August not normally the main season for intense North Indian Ocean tropical cyclones?
Because the southwest monsoon produces strong vertical wind shear.
Strong low-level westerlies and upper-level easterlies tend to disrupt the vertical organisation required for cyclone intensification. IMD also notes that many monsoon depressions have relatively short oceanic tracks before reaching the east coast.
This is a classic example of why:
Warm water ≠ automatic cyclone
Main Cyclone Seasons around India
North Indian Ocean cyclones show two broad peaks:
Pre-monsoon → April–May
Post-monsoon → October–December
The post-monsoon season is particularly significant for the Bay of Bengal and India's east coast.
The retreating monsoon season therefore overlaps with an important cyclone season.
Why Is India's East Coast Highly Vulnerable?
The Bay of Bengal frequently generates cyclones that move towards:
- Odisha,
- West Bengal,
- Andhra Pradesh,
- Tamil Nadu,
- Bangladesh,
- Myanmar.
India's east coast also contains:
- densely populated deltas,
- low-lying coastal plains,
- major cities,
- ports,
- agriculture,
- infrastructure.
The combination of hazard + exposure + vulnerability determines disaster losses.
Cyclone Hazards: Wind Is Only One Part
A tropical cyclone can cause damage through several mechanisms:
Very strong winds
Damage:
- houses,
- trees,
- electricity lines,
- communication systems,
- ports.
Extreme rainfall
Can cause:
- river flooding,
- flash floods,
- urban floods,
- landslides.
Storm surge
Often one of the most deadly coastal hazards.
High waves
Threaten:
- boats,
- ports,
- coastal infrastructure.
Salt-water intrusion
Can damage:
- agricultural soil,
- groundwater,
- freshwater ponds.
What Is a Storm Surge?
A storm surge is an abnormal rise of sea level generated by a storm above the normal expected sea level.
Strong onshore winds push seawater towards the coast.
Low central pressure also contributes.
Storm-surge height depends strongly on:
- cyclone intensity,
- wind field,
- direction of approach,
- coastline shape,
- coastal bathymetry.
A shallow continental shelf can produce a much larger surge because water is piled up more easily near the coast. IMD identifies storm surge as one of the greatest killers associated with tropical cyclones.
Storm Surge vs Storm Tide
Do not confuse them.
Storm Surge = abnormal rise caused by the storm
Storm Tide = storm surge + astronomical tide interaction
If cyclone landfall occurs around high tide, coastal inundation can become much worse.
Why Are Deltas Especially Vulnerable?
Deltas such as the:
- Ganga-Brahmaputra,
- Mahanadi,
- Godavari,
- Krishna
are often:
- low lying,
- flat,
- densely populated,
- cut by rivers and distributaries.
A storm surge can travel inland across such landscapes relatively easily.
This is why cyclone vulnerability cannot be understood through wind speed alone.
Mangroves as Natural Coastal Defence
Mangroves cannot stop a powerful cyclone.
But healthy mangrove belts can reduce coastal vulnerability by:
- dissipating wave energy,
- slowing water flow,
- stabilising sediment,
- reducing erosion,
- providing a buffer between sea and settlement.
Therefore mangrove conservation is part of ecosystem-based disaster-risk reduction.
For Mains, connect:
Cyclones → Storm Surge → Mangroves → Coastal Resilience
How Are Tropical Cyclones Named?
Cyclone naming improves communication.
It helps:
- governments,
- meteorological agencies,
- media,
- emergency services,
- public
refer to the same system clearly.
For the North Indian Ocean, naming is organised under the WMO/ESCAP Panel on Tropical Cyclones.
RSMC New Delhi, operated by IMD, assigns names to tropical cyclones over the Bay of Bengal and Arabian Sea from the approved list. The present system includes names contributed by 13 Panel members, and names on the North Indian Ocean list are not reused after use.
Prelims trap
Cyclones are not personally named after a particular victim, scientist or politician.
Names come from pre-approved regional lists.
IMD Colour-Coded Weather Warnings
UPSC Mains 2022 directly tested this topic.
The broad communication logic is:
Green → No significant warning
Yellow → Be aware / stay updated
Orange → Be prepared
Red → Take action
The purpose is not merely meteorological classification.
It converts technical forecasting into actionable public communication.
A good Mains answer should therefore connect colour warnings with:
- early action,
- evacuation,
- fishing restrictions,
- transport management,
- disaster preparedness.
Why Sea-Surface Temperature Matters
UPSC Mains 2024 asked directly:
What is sea surface temperature rise? How does it affect the formation of tropical cyclones?
A tropical cyclone obtains energy from warm ocean water.
Higher SST can increase:
evaporation → atmospheric moisture → condensation → latent heat release
This can create more favourable conditions for cyclone intensification.
But the UPSC-quality answer needs one important qualification:
SST alone does not determine cyclone formation or frequency.
A cyclone still requires:
- favourable wind shear,
- moisture,
- atmospheric instability,
- sufficient Coriolis force,
- a disturbance.
Sea-Surface Temperature vs Ocean Heat Content
This distinction can improve a Mains answer.
Sea-Surface Temperature
Temperature near the ocean surface.
Ocean Heat Content
Heat stored through a deeper layer of ocean water.
A cyclone passing over deep warm water may continue drawing energy even when its winds mix the ocean.
Therefore deeper ocean warmth can be especially important for rapid intensification.
Climate Change and Tropical Cyclones
Avoid writing:
“Climate change simply causes more cyclones.”
That is too crude.
A better framework is:
Ocean warming can provide more energy and moisture to storms.
A warmer atmosphere can also hold more water vapour.
Therefore warming can contribute to:
- heavier cyclone rainfall,
- higher potential intensity,
- greater probability of rapid intensification under favourable conditions,
- stronger coastal impacts when combined with sea-level rise.
But changes in cyclone frequency are more complicated because cyclone formation also depends on atmospheric circulation and wind shear.
Mains-ready conclusion
Climate change should be understood primarily as a risk multiplier that can worsen the intensity and impacts of tropical cyclones rather than as a simple one-to-one cause of every cyclone.
What Is Rapid Intensification?
Rapid intensification means a cyclone's wind speed increases very quickly over a relatively short period.
This becomes particularly dangerous close to landfall because:
- forecasts have less time to adjust,
- evacuation windows shrink,
- expected damage can increase quickly.
Conditions favouring it can include:
- very warm water,
- high ocean heat content,
- moist atmosphere,
- weak vertical wind shear,
- efficient storm structure.
This is an important emerging area linking:
Climatology + Oceanography + Disaster Management
Fujiwhara Effect: The Latest UPSC Signal
UPSC Mains 2026 asked:
“What is the Fujiwhara effect? Explain its impact on the movement and intensity of tropical cyclones.”
The question appeared in GS Paper I as a 10-mark question.
This makes the Fujiwhara Effect a must-know concept.
What Is the Fujiwhara Effect?
When two tropical cyclones come sufficiently close, their circulations can begin interacting.
Instead of moving independently, the two cyclones may rotate cyclonically around a common centre.
This interaction is called the:
Fujiwhara Effect.
NOAA defines it as the tendency of two nearby tropical cyclones to rotate cyclonically around each other.
Simple Diagram
Cyclone A ↘
● Common Centre
Cyclone B ↖
Both systems may revolve around this common centre.
How Does Fujiwhara Affect Cyclone Tracks?
The interaction can produce:
- curved tracks,
- looping movement,
- unexpected direction changes,
- slower or faster movement,
- increased forecasting uncertainty.
Therefore a cyclone's path may no longer be controlled only by the larger-scale steering winds.
The neighbouring cyclone itself becomes part of the steering environment.
What Happens to Cyclone Intensity?
Several outcomes are possible.
Both remain separate
They orbit each other before separating.
One dominates
A stronger and larger cyclone may strongly influence the weaker cyclone.
Merger
Under some situations the weaker circulation may be absorbed into the stronger system.
Intensity changes
The interaction can alter:
- moisture supply,
- wind shear,
- circulation structure,
- track over warm or cooler water.
Therefore Fujiwhara interaction does not automatically mean intensification.
Its impact depends on the properties of the two storms and the surrounding atmosphere.
This nuance is important for Mains.
Five Most Important PYQs
PYQ 1 — UPSC Mains 2026
What is the Fujiwhara effect? Explain its impact on the movement and intensity of tropical cyclones.
What UPSC wanted
Not a full chapter on cyclones.
It wanted:
Definition → Mechanism → Track impact → Intensity impact
Ideal answer structure
Start with two nearby cyclonic vortices.
Draw a tiny common-centre diagram.
Then discuss:
- mutual rotation,
- track deflection,
- possible orbiting,
- possible merger,
- changes in intensity,
- forecasting difficulty.
PYQ 2 — UPSC Mains 2024
What is sea surface temperature rise? How does it affect the formation of tropical cyclones?
Core demand
Connect:
Ocean warming → evaporation → moisture → latent heat → cyclogenesis/intensification
But add the balance:
SST is necessary but not sufficient.
Wind shear, Coriolis force and atmospheric instability still matter.
PYQ 3 — UPSC Mains 2022
Discuss the meaning of colour-coded weather warnings for cyclone prone areas given by India Meteorological Department.
Core demand
Green → Yellow → Orange → Red
But a higher-quality answer explains why these warnings matter:
forecast → communication → preparedness → evacuation → reduced mortality
PYQ 4 — UPSC Prelims 2015
UPSC asked why tropical cyclones do not normally originate in the South Atlantic and south-eastern Pacific tropical regions.
The exam lesson is more important than memorising the option:
Cyclogenesis requires several conditions to coincide, including a favourable ITCZ/disturbance environment—not merely tropical latitude and warm water.
PYQ 5 — UPSC Mains 2014
“Tropical cyclones are largely confined to South China Sea, Bay of Bengal and Gulf of Mexico. Why?”
Core demand
Explain the geographical concentration through:
- warm water,
- adequate Coriolis force,
- moisture,
- instability,
- disturbances,
- favourable wind shear.
The answer must explain why these basins are favourable, not merely define a cyclone.
Prelims High-Value Facts
Remember these before the exam:
Cyclone → low-pressure system
Tropical cyclone → warm core
Eye → relatively calm
Eyewall → strongest winds
Energy → latent heat of condensation
Minimum warm-water benchmark → around 26.5°C
Equator → cyclogenesis highly unfavourable because Coriolis is weak
Northern Hemisphere → counter-clockwise
Southern Hemisphere → clockwise
Vertical wind shear → strong shear inhibits organisation
Bay of Bengal → historically more cyclones than Arabian Sea
Peak SW monsoon → strong wind shear suppresses intense cyclogenesis
Storm surge → abnormal sea-level rise due to storm
Storm tide → surge + astronomical tide interaction
Fujiwhara → interaction of two nearby cyclones
12 Dangerous Prelims Traps
Trap 1
Cyclones form wherever SST exceeds 26.5°C.
Wrong.
Several atmospheric conditions are also necessary.
Trap 2
Cyclones commonly form at the Equator.
Wrong.
Coriolis force is too weak.
Trap 3
The eye contains the strongest winds.
Wrong.
The eyewall normally does.
Trap 4
Tropical cyclones are cold-core systems.
Wrong.
They are warm-core.
Trap 5
Tropical cyclones contain well-developed warm and cold fronts.
Wrong.
That is characteristic of extratropical cyclones.
Trap 6
Strong vertical wind shear favours cyclone formation.
Wrong.
It generally disrupts vertical organisation.
Trap 7
Arabian Sea does not produce tropical cyclones.
Wrong.
It produces fewer historically, but can produce intense storms.
Trap 8
Peak southwest monsoon is automatically India's strongest cyclone season.
Wrong.
Strong vertical wind shear limits intensification.
Trap 9
Storm surge and storm tide are identical.
Wrong.
Storm tide includes astronomical tide interaction.
Trap 10
Landfall means the outer rainbands first touch the coast.
Wrong.
It refers to the storm centre crossing the coastline.
Trap 11
Fujiwhara interaction always produces a stronger cyclone.
Wrong.
Possible outcomes vary.
Trap 12
Climate change necessarily means more cyclones every year.
Wrong.
Intensity and rainfall risks may rise, while frequency response is more complex.
Five UPSC-Level Practice MCQs
Q1. With reference to tropical cyclones, consider the following conditions:
- Warm ocean water
- Sufficient Coriolis force
- Low vertical wind shear
- Moist and unstable atmosphere
Which of the above favour tropical cyclone development?
A. 1 and 2 only
B. 1, 2 and 3 only
C. 2, 3 and 4 only
D. 1, 2, 3 and 4
Answer: D
Explanation: All four conditions are important.
Warm ocean water supplies energy, Coriolis force supports rotation, low wind shear maintains the vertical structure, and atmospheric moisture/instability sustains convection.
Why the other options are wrong: Each leaves out at least one important ingredient.
Extra fact: A pre-existing atmospheric disturbance is also generally necessary.
Q2. Which one of the following correctly describes the eyewall of a mature tropical cyclone?
A. Region of descending dry air with weakest winds
B. Region surrounding the eye containing the strongest winds and intense convection
C. Outer edge where Coriolis force disappears
D. Area where warm and cold fronts intersect
Answer: B
Explanation: The eyewall contains intense thunderstorms, strong uplift and usually the maximum winds.
Why others are wrong:
A describes the eye more closely.
C has no basis.
D applies to frontal/extratropical systems.
Extra fact: The eye itself may be relatively calm even though pressure is lowest there.
Q3. Why are intense tropical cyclones comparatively uncommon over the North Indian Ocean during peak southwest monsoon?
A. Sea-surface temperatures become too low everywhere.
B. Coriolis force disappears.
C. Strong vertical wind shear disrupts cyclone organisation.
D. Atmospheric moisture becomes absent.
Answer: C
Explanation: Strong low-level westerlies and upper-level easterlies create considerable vertical wind shear during the monsoon.
Why others are wrong: Oceans remain warm and humid, while Coriolis force obviously continues to operate.
Q4. With reference to storm surge, consider the following statements:
- It is an abnormal rise of sea level associated with a storm.
- Shallow coastal bathymetry can increase its height.
- It is identical to astronomical high tide.
Which statements are correct?
A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2 and 3
Answer: B
Explanation: Storm surge is storm-generated abnormal water rise, and shallow coastal waters can magnify it.
Statement 3 is wrong.
Storm tide = storm surge interacting with astronomical tide.
Q5. The Fujiwhara Effect refers to:
A. rapid intensification caused only by warm ocean water
B. splitting of one cyclone into two independent storms
C. mutual interaction and cyclonic rotation of two nearby tropical cyclones
D. conversion of a tropical cyclone into a temperate cyclone
Answer: C
Explanation: Nearby cyclone circulations can rotate around a common centre and modify each other's tracks.
Why others are wrong: Fujiwhara is a binary cyclone-interaction phenomenon, not a term for SST-driven intensification or extratropical transition.
Mains Question 1
Explain the conditions necessary for the genesis and intensification of tropical cyclones.
Framework
Introduction: Tropical cyclone as a warm-core rotating low-pressure system.
Body:
- SST around/above 26.5°C
- deep warm-water layer
- sufficient Coriolis force
- pre-existing disturbance
- atmospheric moisture
- instability
- low vertical wind shear
- upper-level divergence/outflow
Draw:
Warm Ocean → Moist Convection → Latent Heat → Pressure Fall → Rotation → Cyclone
Conclusion: Cyclogenesis requires simultaneous oceanic and atmospheric favourability.
Mains Question 2
Why is the Bay of Bengal historically more cyclone-prone than the Arabian Sea?
Framework
Discuss:
- warmer/favourable Bay conditions historically,
- disturbances generated in situ,
- contribution of remnants from western Pacific systems,
- Bay's position relative to Andaman Sea/South China Sea pathways,
- fewer surviving systems crossing peninsula into Arabian Sea.
Add balance:
Arabian Sea is not cyclone-free and can produce severe storms.
Mains Question 3
Rising ocean temperatures are changing cyclone risk even where cyclone frequency does not increase proportionately. Discuss.
Framework
Ocean warming
↓
greater evaporation
↓
more moisture
↓
larger latent-heat supply
↓
potential for stronger rainfall/intensification
Add:
- Ocean Heat Content,
- rapid intensification,
- sea-level rise + storm surge,
- exposure of coastal cities.
Balance with:
- wind shear,
- circulation,
- ENSO and other controls.
Mains Question 4
Explain why storm surge often causes greater human losses than the winds of a tropical cyclone.
Framework
Discuss:
- abnormal sea-level rise,
- low-lying deltas,
- shallow continental shelf,
- high tide interaction,
- rapid inland inundation,
- salinisation,
- dense population,
- damage to transport/evacuation routes.
Way forward:
- evacuation,
- mangroves,
- cyclone shelters,
- coastal zoning,
- impact-based forecasting.
Mains Question 5
What is the Fujiwhara Effect? Why does it present a challenge to tropical cyclone forecasting?
Framework
Introduction: Binary interaction between nearby cyclones.
Mechanism: Mutual circulation → rotation around common centre.
Effects:
- track deflection,
- looping,
- altered speed,
- possible separation,
- possible merger,
- intensity changes.
Forecasting challenge:
Track depends on both:
environmental steering + interaction between storms
Conclusion: Better coupled numerical modelling is necessary for high-confidence track forecasts.
How to Draw a Tropical Cyclone in Mains
A simple labelled diagram should contain:
Eye
↓
Eyewall
↓
Spiral Rainbands
Add arrows showing:
Surface inflow → Rising air → Upper-level outflow
Do not spend three minutes making an artistic cyclone.
A 20-second labelled sketch is enough.
One High-Value Conceptual Chain
Remember this:
Warm Ocean
↓
Evaporation
↓
Moist Air Rises
↓
Condensation
↓
Latent Heat Released
↓
Air Warms and Rises More
↓
Pressure Falls
↓
More Surface Air Converges
↓
Coriolis Produces Rotation
↓
Cyclone Intensifies
This one chain can answer a large part of the 2024 SST question.
60-Second Revision
Tropical Cyclone → Warm-core low-pressure system
Energy → Latent heat
SST → Around 26.5°C+ through sufficient depth
Coriolis → Necessary for organised rotation
Equator → Cyclogenesis rare
Wind Shear → Low shear favourable
NH → Counter-clockwise
SH → Clockwise
Eye → Calm, lowest pressure
Eyewall → Strongest winds
Bay of Bengal → Historically more cyclones
Peak SW monsoon → Strong shear inhibits intense cyclone development
Cyclonic Storm → 62 km/h or more under IMD classification
Landfall → Cyclone centre crosses coast
Storm Surge → Abnormal storm-driven sea-level rise
Storm Tide → Surge + astronomical tide
Naming → WMO/ESCAP list; RSMC New Delhi for North Indian Ocean
SST Rise → More available heat/moisture, but not sufficient alone
Fujiwhara Effect → Two nearby cyclones interact and rotate around a common centre
Final Takeaway
Tropical cyclones should not be memorised simply as violent storms that develop over warm seas.
UPSC's PYQs show a more sophisticated demand.
Warm ocean water explains the energy source.
Coriolis force explains rotation.
Wind shear explains why some disturbances organise while others collapse.
Ocean-basin geography explains distribution.
Storm surge explains much of the coastal disaster risk.
Sea-surface warming connects cyclones with climate change.
And the latest Fujiwhara question shows that UPSC can move from basic cyclone formation to the interaction between two complex atmospheric vortices.
The most useful way to remember the chapter is therefore:
Ocean provides the energy, atmosphere controls the organisation, geography shapes the hazard, and vulnerability determines the disaster.
Reliable Sources
India Meteorological Department / RSMC New Delhi — Tropical Cyclone FAQs
NCERT — Fundamentals of Physical Geography
