Distribution of Tropical Cyclones

Tropical cyclones do not form everywhere in the tropics. Instead, they are largely confined to 5°–15° latitudes in both hemispheres, over warm ocean waters. From there, they affect the coastal regions of continents.

Broadly, there are six major cyclone-prone regions of the world:

1. West Indies, Gulf of Mexico, Caribbean Sea
2. Western North Pacific Ocean (Philippines, South China Sea, Japan)
3. North Indian Ocean (Arabian Sea & Bay of Bengal)
4. Eastern Pacific Ocean (off Mexico & Central America)
5. South Indian Ocean (off Madagascar, Mauritius, Réunion)
6. South Pacific Ocean (Samoa, Fiji, northeast Australia)

Now let’s look at each basin in detail.

1. North Atlantic Ocean (Hurricanes)

• Frequency: ~7 per year (many become full-fledged hurricanes).
• Seasonal rhythm:
  • Cape Verde (off West Africa): August–September.
  • West Indies / South Atlantic coast of USA: June–October.
  • North Caribbean: May–November.
  • South Caribbean: June–October.
  • Gulf of Mexico: June–October.
• 👉 These are the classic Atlantic hurricanes that often hit the USA, Caribbean islands, and Central America.

2. Eastern North Pacific Ocean

• Cyclones form off Mexico’s west coast.
• Movement: Drift northwest → sometimes hit California and Hawaii.
• Frequency: ~5 per year (2 reach hurricane intensity).
• Season: June–November.

3. Western North Pacific Ocean (Typhoons)

• Covers Philippines, South China Sea, Japan.
• Season: May–December.
• Frequency: Highest in the world → about 12 typhoons annually.
• 👉 Eastern China, Taiwan, and Japan often face disastrous typhoons.

4. South Pacific Ocean

• Affects northeast Australia and islands east of 180° longitude (e.g., Society Islands, Fiji, Samoa).
• Season: December–April.
• 👉 These are the storms Australians call “willy-willies.”

5. North Indian Ocean (Cyclones & Depressions)

• Cyclones originate in Bay of Bengal and Arabian Sea.
• Season: April–December.
• 👉 They have a huge influence on Indian weather, especially:
  • Pre-monsoon cyclones (May–June).
  • Post-monsoon cyclones (Oct–Nov).
• Bangladesh, Odisha, Andhra, West Bengal, and Tamil Nadu are highly vulnerable due to funnel-shaped coasts.

6. South Indian Ocean

• Cyclones originate off Madagascar, Réunion, Mauritius.
• Season: November–April.
• 👉 They often devastate Madagascar and island nations.

✅ Key Takeaways for UPSC

• Global hotspots: North Atlantic (hurricanes), Western Pacific (typhoons), North Indian Ocean (cyclones).
• Seasonality: Different in each basin but always linked to warm ocean months.
• Frequency:
  • Highest = Western North Pacific (~12/year).
  • Moderate = North Atlantic (~7/year).
  • Lower = Indian Oceans (few per year but often deadlier due to dense coastal populations).
• Regional names: Hurricane (Atlantic/USA), Typhoon (Pacific/China/Japan), Cyclone (Indian Ocean), Willy-willy (Australia).

👉 In exam terms, always remember: “Bay of Bengal + Western Pacific” = deadliest cyclone basins, due to geography (funnel coasts, shallow seas, dense population).

Changing Cyclone Patterns in the Indian Ocean

Traditionally, the North Indian Ocean (Bay of Bengal + Arabian Sea) has been a low-frequency but high-impact cyclone basin. But in recent decades, patterns have shifted significantly.

📈 Rising Frequency & Intensity

• In recent times, high-intensity storms are becoming more common.
• Cyclones are now forming even in off-season months like January.
• Some storms follow unusual, unpredictable paths — e.g., Cyclone Titli (2018), which changed track abruptly and devastated Odisha & Andhra Pradesh.

👉 This shows that cyclones are no longer restricted to traditional seasonal windows or predictable tracks.

🌡️ Global Warming & Ocean Temperatures

• South Indian Ocean: Earlier ~26.5°C, now 30–32°C surface temperatures.
• Regions further from the equator are also now touching the critical threshold (24–26°C) required for cyclogenesis.
• This has expanded the geographical range of cyclone formation → both frequency & intensity have increased.

Global Climatic Drivers Exacerbating the Change:

• El Niño
• Indian Ocean Dipole (IOD)
• Southern Annular Mode
• Madden-Julian Oscillation (MJO)

👉 All of these are themselves influenced by climate change, making cyclones more erratic and powerful.

Example: Cyclone Idai (2019) in Mozambique → one of the deadliest in Africa (1000+ deaths). Warmer oceans sustained its intensity.

🌊 Cyclone Patterns in the Arabian Sea

Traditionally, the Arabian Sea was less cyclone-prone than the Bay of Bengal, because:

• The Findlater/Somali Current → causes upwelling of cold water, cooling the sea surface.
• Result: ~50% of storms here did not sustain.

But this has changed:

• Earlier: one Extremely Severe Cyclone once in 4–5 years.
• Now: multiple severe cyclones in short intervals.
  • 1998–2013 (15 years): 5 extremely severe cyclones.
  • 2014 Nilofar (Category 4): impacted west coast of India.
  • 2015: Within a single week → Cyclone Chapal + Cyclone Megh (even stronger).

👉 The Arabian Sea is warming rapidly, fueling cyclones that were previously rare in this basin.

🌏 Role of El Niño Modoki

• El Niño Modoki = “pseudo El Niño” → warming occurs in central Pacific, unlike the eastern Pacific warming of traditional El Niño.
• Effect on Indian Ocean cyclogenesis:
  • Bay of Bengal: Not favourable (suppresses cyclone activity).
  • Arabian Sea: Increases convergence & cyclogenesis, leading to more cyclones here.

👉 This explains the recent shift of cyclone activity from Bay of Bengal to Arabian Sea.