As Cyclone Arnab approaches, a look at the science behind naming of cyclones

Arnab is an identifying name for a tropical cyclone. The name helps weather agencies, governments, media organisations and the public discuss one storm clearly. It does not describe the storm’s strength, forecast path or likely damage. The article presents Arnab among names such as Amphan, Fani and Biparjoy.

A North Indian Ocean system qualifies for a name when its maximum sustained surface wind speed reaches 34 knots, or approximately 62 kilometres per hour. This rule means that simply forming over the sea, producing rain or threatening bad weather is not enough. The system must reach the prescribed wind-speed threshold.

The India Meteorological Department names qualifying systems using the regional list. Names are used sequentially, regardless of which country a storm may eventually affect. Arnab’s name therefore identifies the system, while its danger must be judged from wind, rainfall, storm surge, movement and the vulnerability of places along its path.

The India Meteorological Department, or IMD, names tropical cyclones that develop over the North Indian Ocean. This region includes both the Bay of Bengal and the Arabian Sea. The responsibility is carried out through the IMD’s Regional Specialised Meteorological Centre in New Delhi.

The system is regional rather than controlled by India alone. Thirteen countries submit names, which are compiled into a shared list. Those countries are Bangladesh, India, Iran, the Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, the United Arab Emirates and Yemen.

Names are selected in sequence after a storm meets the required wind threshold. The country that contributed a name does not determine which storm receives it. A name submitted by one country may be assigned to a cyclone that later affects another country, so the name does not predict landfall.

The North Indian Ocean naming threshold is 34 knots. This equals approximately 62 kilometres per hour in the article. The threshold applies to maximum sustained surface wind speed, rather than to rainfall, size or the number of countries threatened.

This rule prevents every tropical disturbance from receiving a formal name. A system may develop over the sea or be forecast to bring rain, but those facts alone do not qualify it. It must first reach the prescribed wind speed. Once it does, the next name in the regional list is used.

The threshold makes naming a consistent meteorological decision. It also separates identification from prediction. A named storm is not automatically the most dangerous possible storm, and its name does not show where it will land. Officials must still assess wind, rainfall, surge, movement and local vulnerability.

The North Indian Ocean naming list is a multinational system. Thirteen countries contribute names instead of leaving the process to one country. This arrangement covers cyclones developing over the Bay of Bengal and the Arabian Sea, with the India Meteorological Department coordinating naming through its regional centre.

The list introduced in 2020 contains 169 names. The total comes from 13 countries, each contributing 13 names. Once a storm reaches the 34-knot wind threshold, names are taken sequentially from this regional list. The storm’s eventual landfall does not decide which name it receives.

The large list also reflects a key regional rule: a name is not reused after it has been used. This differs from the Atlantic, where six rotating lists return every six years and especially destructive names may be retired. The North Indian Ocean therefore relies on a broad, one-time-use sequence.

Naming turns a complicated weather system into a clearly identifiable event. Weather agencies, governments, media organisations and the public can use one short name when sharing forecasts, warnings and updates. This makes communication faster and less ambiguous during dangerous weather.

The benefit is especially clear when multiple weather systems are active at the same time. Instead of describing a storm repeatedly by its location or technical details, officials can refer to its assigned name. In India, the name comes from a regional list after the system reaches the prescribed wind threshold.

A name improves coordination, but it does not replace hazard information. The name does not measure strength or reveal where landfall will occur. People must still follow official updates and consider wind speed, rainfall, storm surge, movement and the vulnerability of areas in the storm’s path.

Naming systems differ by ocean basin. The North Indian Ocean uses a regional list prepared by 13 countries, and names are assigned sequentially. Once a name has been used, it is not used again. This creates a long list rather than a repeating cycle.

The Atlantic follows another model. It uses six rotating lists, with each list returning every six years. However, a name may be retired when a storm is especially deadly or destructive. Retirement prevents that name from returning because of the loss of life or devastation associated with the storm.

The contrast shows that there is no single worldwide naming list or rule. Regional meteorological arrangements decide how names are selected and reused. In the North Indian Ocean, the one-time-use rule means a previously assigned name remains permanently unavailable, regardless of how severe that storm was.

A cyclone’s name is only an identification tool. It does not measure strength, predict damage or show whether a storm is dangerous. The name helps people follow one system, but it cannot replace official hazard information or local warnings.

The article identifies several factors that determine danger: wind speed, rainfall, storm surge, movement and the vulnerability of areas in the cyclone’s path. For example, a storm’s effects depend not only on its winds but also on how much rain it brings, where it moves and how exposed nearby communities are.

This means a named cyclone should never be judged by its name alone. The 34-knot threshold only determines when a North Indian Ocean system receives a name. Governments and the public must continue monitoring official updates, because the actual risks can change with the storm’s movement and conditions in affected areas.