October is cyclone season on India’s east coast, and it is no accident. Warm Bay water, calm winds and leftover monsoon systems line up every year for Odisha.
Updated: October 25, 2026, 10:30 AM IST
Quick Read
- October-November and May-June are the two peak cyclone seasons in the North Indian Ocean, with an average of five severe storms a year. In 131 years, 61 storms formed in the Bay of Bengal in October alone.
- A cyclone needs sea water of at least 26.5°C. The Bay of Bengal sits around 29–30°C in October, land-locked and warm, with moist air and weak wind shear on top.
- For every cyclone over the Arabian Sea, about four form over the Bay of Bengal. Odisha’s long, low coastline takes the hit most often — which is why its disaster teams drill for this every year.
Every October, the same question comes back to Odisha: why here, why now? Cyclone Arnab, building over the Bay of Bengal this weekend, is the latest answer. The short version is that October is when the sea is warmest, the air is wettest and the winds are calmest — three ingredients a cyclone needs, all arriving together. The longer version explains why the Bay of Bengal, more than almost any sea on Earth, keeps serving them up.
The recipe: warm water, moist air, calm winds
Think of a cyclone as an engine that runs on warm seawater. For one to form, the sea surface has to reach at least 26.5°C, and the warm water has to run deep — at least 50 metres down. Meteorologists quoted by The Business Standard put it plainly: warm water is the fuel, and it speeds the storm up as it moves over hotter patches. After the summer and the monsoon, the Bay of Bengal holds its heat. It is ringed by land, so no cold ocean current flows in to cool it, and its surface sits around 29 to 30°C in October.
Then comes the monsoon retreat. When the southwest monsoon pulls back in late September and October, the air over the Bay stays wet, and leftover weather systems drifting in from the South China Sea find warm, welcoming water. Vajiram and Ravi’s explainer on October storms notes that this is when remnant systems get the conditions they need to grow. Add one more factor — weak vertical wind shear, meaning winds at different heights blow in roughly the same direction — and the storm’s tower of clouds stays standing instead of getting sheared apart. Warm sea, wet air, steady winds. That is the recipe, and October serves it reliably.
Our report on Cyclone Arnab’s track and the school closures shows the recipe in action this week: a low-pressure area on October 23, a depression by October 25, a storm by October 26, landfall by October 28. Each step needs the sea to stay warm. If it cools, or the shear picks up, the storm stalls. That is also why not every low-pressure area becomes a cyclone — in September this year, one system crossed the Andhra-Odisha coast as a mere deep depression, ABP Live noted. The ingredients were close, but not quite there.
Why the Bay beats the Arabian Sea, four to one
The numbers are stark. The Regional Specialised Meteorological Centre counts about four Bay of Bengal cyclones for every one over the Arabian Sea. Between 1990 and 2020, the Arabian Sea produced 73 tropical cyclones and the Bay produced 190, according to an IMD climatology study cited by IPE Global. Three reasons explain it, and all of them are geography.
First, temperature. The Arabian Sea loses heat to strong winds and evaporation, and it stays cooler for most of the year. The Bay, shut in by land, stays hot. Second, moisture. Dry air blows into the Arabian Sea from the deserts of Oman and Yemen, and dry air starves a cyclone. The Bay’s air is wet. Third, the systems themselves: the Bay catches weather systems travelling west from the South China Sea, while the Arabian Sea has no such steady supply line. Put together, the Bay is simply a better factory.
Why Odisha, specifically
Odisha has a long coastline facing the Bay, and much of it is low-lying. When a storm pushes seawater ashore — the storm surge — there is little height to stop it, and rivers already full from the monsoon can spill over. The state has faced many of its worst storms in October, including the super cyclone of 1999, which remains the benchmark every disaster plan is measured against. In 131 years of records, October alone has produced 61 Bay of Bengal storms, the RSMC figures show. That history is why Odisha’s response looks so rehearsed: 60 ODRAF teams, 17 NDRF teams and 225 fire teams were on alert before Arnab even had a name.
How storms get names like Arnab
Cyclone names come from a shared list maintained by the World Meteorological Organization and the IMD, with countries around the North Indian Ocean taking turns to contribute. Bangladesh offered Arnab, which means “ocean” in Bengali, ABP Live reported. The list exists for a simple, practical reason: a named storm is easier to warn about than “the well-marked low-pressure area over the east-central Bay of Bengal.” Short names travel faster on radio, TV and phone alerts. They also help people remember one storm from the next when two systems brew in the same season.
What to do when the warning comes
Warnings work only if people act on them, and the basics have not changed. Don’t go out to sea when fishermen are told to stay back. Move to a shelter if your district orders an evacuation — don’t wait to see the storm. Charge your phone, keep drinking water and dry food ready, and keep your identity papers in a plastic bag. If you live in a low-lying area near the coast, find out now which shelter your panchayat or ward has marked, not when the rain starts. And check the IMD bulletin, not a forwarded video: the official track moves every few hours, and old tracks mislead.
One honest caveat runs through all of this. Cyclone science can say a lot about October in general and very little about one storm’s exact landfall four days out. Arnab’s track will narrow as it forms, and the Monday-morning bulletin will tell Odisha and Andhra Pradesh far more than today’s forecast can. The season is predictable. The storm, until it forms, is not.
Also read
- Cyclone Arnab: 5 Odisha districts shut schools Oct 28
- Tibet 7.0 quake kills 16, 339 homes collapse
- Why Tibet shakes: the fault line under India
FAQ
Why do cyclones form in October? After the monsoon retreats, the Bay of Bengal stays warm (around 29–30°C), the air stays moist, and wind shear stays weak. Those three conditions together let low-pressure systems grow into cyclones.
Why does the Bay of Bengal get more cyclones than the Arabian Sea? It is warmer, wetter and ringed by land, so no cold water cools it, and it catches weather systems from the South China Sea. The count is roughly four Bay cyclones for every one Arabian Sea cyclone.
Who named Cyclone Arnab? Bangladesh contributed the name to the regional list maintained by the WMO and the IMD. Arnab means “ocean” in Bengali.
