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:
- Tropical Disturbances (Easterly Waves)
- Tropical Depressions
- Tropical Storms
- 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
Feature | Hurricanes (Tropical) | Temperate Cyclones |
Isobars | Circular, symmetrical, steep gradient | Elongated, wave-like |
Rainfall | Heavy, uniform, widespread | Confined to warm/cold fronts |
Temperature variation | None | Clear contrasts (warm vs cold sectors) |
Wind direction | Inward, rising vertically | Variable, shifting with fronts |
Movement | East → West | West → East |
Association with Anticyclones | Not associated | Often 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.