Social media posts and digital headlines have widely referred to a weather system over the Bay of Bengal as “Cyclone Arnab”. However, the India Meteorological Department has not officially classified the system as a cyclone and has not assigned it that name.
The system was classified as a deep depression as it approached the north Andhra Pradesh and south Odisha coasts. It crossed the coast near Kalingapatnam between late September 23 and early September 24, bringing strong winds and heavy rain. IMD said the system had maximum sustained winds of around 55–65 kmph, with gusts reaching up to 75 kmph.
As of Thursday, September 24, IMD said the deep depression was located over north coastal Andhra Pradesh and adjoining south Odisha and was moving north-northwestwards. The department expected it to weaken gradually into a depression later in the day.
What separates a deep depression from a cyclone?
The distinction is primarily based on the maximum sustained wind speed associated with the system.
Under the IMD's classification:
- A depression has maximum sustained winds of 31–50 kmph, or 17–27 knots.
- A deep depression has maximum sustained winds of 52–61 kmph, or 28–33 knots.
- A cyclonic storm has maximum sustained winds of at least 63 kmph, or 34 knots.
IMD's cyclone classification also uses the structure of the pressure field, including the number of closed isobars. A depression has two closed isobars, while a deep depression has three. A cyclonic storm has four or more closed isobars.
IMD's own cyclone reports similarly classify 28–33-knot systems as deep depressions and 34–47-knot systems as cyclonic storms.
The current system has therefore remained below the threshold required for it to be officially classified as a cyclonic storm. That is why the name “Arnab” has not been formally assigned to it.
Why is ‘Arnab’ being mentioned?
“Arnab” is not an invented name circulating only on social media. It is an official name in the North Indian Ocean's tropical cyclone naming list.
The name was contributed by Bangladesh and appears in the WMO/ESCAP Panel's official list of names for cyclones forming over the Bay of Bengal and Arabian Sea. The list is maintained under the regional cyclone-naming system involving 13 member countries, including Bangladesh, India, Pakistan, the Maldives and Oman.
The names are arranged sequentially. The Regional Specialised Meteorological Centre in New Delhi, operated by IMD, is responsible for naming systems over the North Indian Ocean once they reach the required intensity.
The official list places “Arnab” among Bangladesh's contributed names. It therefore becomes relevant when a qualifying system reaches cyclonic-storm intensity and the naming sequence reaches that entry. Until then, the name remains on the list rather than being attached to every depression or deep depression.
Why the system remains dangerous despite not being a cyclone
The absence of a cyclone name does not mean that the weather system poses little risk.
Deep depressions can bring intense rainfall, strong winds, rough seas, flash flooding and landslides. The current system has already produced significant weather impacts across parts of eastern and southern India.
Before and during landfall, authorities in Odisha and Andhra Pradesh took precautionary measures, including school closures and preparations for evacuation in vulnerable areas. Andhra Pradesh shut schools and Anganwadi centres in several districts as the system approached the coast.
In Odisha, authorities also closed schools and Anganwadi centres in affected areas amid heavy to very heavy rainfall and red warnings issued for several districts.
West Bengal was also under weather warnings as the system moved towards the Andhra Pradesh and Odisha coast. The IMD had forecast widespread rainfall, thunderstorms and gusty winds in several parts of the state, with fishermen advised not to venture into the sea.
The system's landfall near Kalingapatnam has not ended the weather threat. IMD said it was likely to move north-northwestwards after crossing the coast and gradually weaken, while heavy rainfall continued to be a concern across affected areas.
What the ‘Arnab’ label means for weather tracking
The key distinction is between a storm's official meteorological classification and the name that would be assigned if it reaches the required intensity.
“Arnab” is an official name in the regional naming roster, but the weather system currently being tracked by IMD is a deep depression. Calling it “Cyclone Arnab” before it reaches cyclonic-storm intensity can therefore create confusion about its official status.
For residents and authorities, the more important information remains the IMD's warnings on rainfall, wind, sea conditions and the system's movement. A weather system does not need to be classified as a cyclone to cause widespread flooding, damaging winds or other serious hazards.