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Types of Tropical Cyclones

Before classifying, let’s remember one key point:
👉 No two tropical cyclones are identical. They differ in size, speed, rainfall, and destructive power.

Still, for our understanding, geographers divide them into four major types:

  1. Tropical Disturbances (Easterly Waves)
  2. Tropical Depressions
  3. Tropical Storms
  4. Hurricanes / Typhoons

On the basis of intensity, these can be grouped as:

  • Weak Cyclones → (i) Tropical disturbances, (ii) Tropical depressions
  • Strong Cyclones → (iii) Tropical storms, (iv) Hurricanes / Typhoons, (v) Tornadoes

Now let’s explore them one by one.

1. Tropical Disturbances (Easterly Waves)

  • These are migratory wave-like cyclones, usually linked with the easterly trade winds.
  • Also called easterly waves because they drift westward under trade winds.
  • Windspeed: Very low. Winds move sluggishly toward the centre.
  • Latitudes: Usually between 5°–20° N, in the western parts of oceans.
  • Rainfall: Associated with cumulus and cumulonimbus clouds → moderate to heavy rain + thunderstorms.
  • Sometimes they remain stationary for days, flooding a region.
  • Many easterly waves intensify into hurricanes (esp. in Caribbean Sea and North Pacific Ocean during summer).

👉 In short: tropical disturbances are the “seeds” of bigger cyclones.

2. Tropical Depressions

  • These are low-pressure centres, surrounded by multiple closed isobars.
  • Size: Very small.
  • Windspeed: Around 40–50 km/h.
  • They sometimes remain stationary, making their path and speed unpredictable.
  • Usually develop near the Inter-Tropical Convergence (ITC), not in trade wind belts.
  • Influence weather in India and northern Australia during summers.
  • In India, many originate in the Bay of Bengal, move north-westward, and bring heavy rain + floods to interior regions.

👉 Example: Seasonal depressions are key players in India’s monsoon rainfall.

3. Tropical Storms

  • These are more organized low-pressure systems with stronger winds.
  • Windspeed: 60–120 km/h.
  • Found in Bay of Bengal, Arabian Sea, Caribbean Sea, Philippines region.
  • They often intensify into violent cyclonic storms, causing:
    • Floods in low-lying areas (Bangladesh, Odisha, Andhra, Tamil Nadu).
    • Storm surges in deltas (esp. Ganga–Brahmaputra delta).

Historical Examples:

  • Bangladesh Cyclone (1970): 3,00,000 deaths.
  • Calcutta Cyclone (1737): Also 3,00,000 deaths.
  • Andhra Cyclone (1977): Winds 175 km/h → 55,000 deaths, 1.2 million hectares ruined.
  • Odisha Super Cyclone (1999): Winds 300+ km/h, 10,000 deaths, ₹1,000 billion property loss.

👉 These storms show why the northern Bay of Bengal is one of the world’s most cyclone-prone regions (due to funnel-shaped coast + flat terrain + astronomical tides).

4. Hurricanes / Typhoons

  • The most violent form of tropical cyclones.
  • Names differ by region:
    • Hurricane → USA, Caribbean
    • Typhoon → China, Japan, Philippines
    • Willy-willy → Australia
    • Cyclone → Indian Ocean
  • Size: Diameter 160–640 km.
  • Pressure: Extremely low at centre (900–950 mb).
  • Windspeed: More than 120 km/h.
  • Eye: A calm, dry, 6–48 sq km zone in the centre with weak winds.
  • Hurricane waves: Storm surges 3–6 m high → coastal flooding.
  • Vertical extent: Up to 12 km into the atmosphere.
  • Duration: Can last over a week.

🔹 Hurricanes vs Temperate Cyclones

FeatureHurricanes (Tropical)Temperate Cyclones
IsobarsCircular, symmetrical, steep gradientElongated, wave-like
RainfallHeavy, uniform, widespreadConfined to warm/cold fronts
Temperature variationNoneClear contrasts (warm vs cold sectors)
Wind directionInward, rising verticallyVariable, shifting with fronts
MovementEast → WestWest → East
Association with AnticyclonesNot associatedOften linked with anticyclones

👉 In short: hurricanes are compact, intense, and energy-packed, while temperate cyclones are larger, more gradual systems driven by fronts.

✅ Summary for UPSC:
  • Disturbances → Depressions → Storms → Hurricanes is the intensity ladder.
  • Bay of Bengal = hotspot of deadly cyclones (historical disasters prove this).
  • Hurricanes/typhoons = most violent, symmetrical, and destructive form, with the lowest pressures recorded.


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