Cyclone Formation: Bay of Bengal vs Arabian Sea

The Bay of Bengal and the Arabian Sea sit on opposite sides of the same peninsula. Yet one breeds cyclones far more often than the other.

Satellite image of Cyclone Amphan (2020), one of the most powerful cyclones ever recorded in the Bay of Bengal. Photo: NASA MODIS Land Rapid Response Team, public domain.

Tropical cyclone tracks in the North Indian Ocean, 1980-2005. The Bay of Bengal sees far more cyclones than the Arabian Sea. Map: Nilfanion, Wikimedia Commons, public domain.

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Indian Geography · IndGeo0057

Two Seas, Very Different Cyclone Habits

Bay of Bengal

SST often 28-32°C, warmer and shallower
Warm river discharge: Ganges, Brahmaputra, Irrawaddy
~4x more cyclones than the Arabian Sea

Arabian Sea

Cooler, stronger evaporative winds
Historically fewer cyclones
Very severe cyclones up ~150% in 4 decades

2004

Formal cyclone naming began, by RSMC New Delhi

WMO/ESCAP member countries sharing the name list

The gap is narrowing

Warming seas are pushing Arabian Sea cyclones to intensify faster than ever — rapid-intensification events have roughly doubled since 2013, closing a gap that once looked permanent.

📑 Contents

1Must Know
2Good to Know
3Test Yourself
4Great to Know
5Current Affairs
6Previous Year Questions

✊ Must Know

Why the Bay of Bengal Breeds More Cyclones

Tropical cyclones need warm ocean water, typically above 26-27°C, to form and intensify.
The Bay of Bengal historically produces far more cyclones than the Arabian Sea, roughly four times as many.
Sea surface temperatures in the Bay of Bengal stay consistently high, often above 28°C, and sometimes exceeding 30-32°C.
The Arabian Sea is generally cooler than the Bay of Bengal, partly due to stronger winds driving more evaporative cooling.
The Bay of Bengal is also shallower than the Arabian Sea. This lets heat transfer more efficiently from the water into the air above.

📘 Good to Know

Rivers, Recycled Typhoons, and Naming Rules

Large rivers, including the Ganges, Brahmaputra, and Irrawaddy, discharge warm freshwater into the Bay of Bengal. This keeps its surface layer warm and less salty.
Pacific typhoons sometimes travel west and weaken into low-pressure systems entering the Bay of Bengal. The bay’s warm waters can then help these systems reintensify into full cyclones.
Since September 2004, tropical cyclones over the North Indian Ocean, covering both the Bay of Bengal and the Arabian Sea, have been formally named.
RSMC New Delhi, part of the India Meteorological Department, is the regional authority responsible for this naming.

Test Yourself

🌟 Great to Know

How Cyclone Naming Actually Works

RSMC New Delhi names cyclones on behalf of 13 member countries under the WMO/ESCAP Panel on Tropical Cyclones.
These members include India, Bangladesh, Pakistan, Sri Lanka, Myanmar, Thailand, Oman, Iran, and several Gulf states.
Each of the 13 countries contributes names to a shared master list, used in rotation as storms form.
A cyclone is officially named once its sustained wind speed reaches at least 34 knots, about 62 km/h.

📰 Current Affairs

A Narrowing Gap

Studies by the Indian Institute of Tropical Meteorology (IITM) found very severe cyclones in the Arabian Sea rose by about 150% over the past four decades. (Source: Carbon Impacts)
Scientists link this shift to rising sea surface temperatures and greenhouse-gas-driven ocean warming. (Source: Nature Communications Earth & Environment)
Meanwhile, the frequency of Arabian Sea cyclones undergoing rapid intensification has roughly doubled since 2013.
This trend is narrowing, though not erasing, the historic gap between the two seas’ cyclone activity.

📝 Previous Year Questions

UPSC Mains 2024 GS Paper I, Q4

Mains PYQ Sea Surface Temperature Rise and Tropical Cyclone Formation

Why Cyclones Skip the South Atlantic and South-East Pacific

Missing ingredient Tropical cyclones need a pre-existing disturbance to grow from. The Inter-Tropical Convergence Zone (ITCZ) usually supplies that.
Why it’s absent The ITCZ stays close to the equator over the South Atlantic and South-Eastern Pacific. It rarely shifts far enough south to seed a storm there.
Not the sea surface Sea surface temperatures and the Coriolis force aren’t the real blockers here. The missing convergence zone is.
Answer: (b) Inter-Tropical Convergence Zone seldom occurs in these regions.
View this question on the full 2015 paper →

A Cyclone’s Eye Is Warmer, Not Colder

Not all cyclones Only some cyclones develop a well-defined eye. It forms only once a cyclone is sufficiently intense and mature.
Warmer, not colder A cyclone’s eye is actually warmer than its surroundings, from warm-core subsidence, not roughly 10°C cooler as sometimes claimed.
Jet streams, separately Jet streams occur in both hemispheres, not just the Northern Hemisphere — see IndGeo0062 — Western Disturbances for that half of this question.
Answer: (c) 2 only, out of the full 3-statement question.
View this question on the full 2020 paper →