Ipsa Tripathy
Bhubaneswar: October is a month of transition over the Indian subcontinent. The southwest monsoon begins withdrawing, the atmosphere changes from the monsoon pattern to the post monsoon circulation, and the Bay of Bengal remains warm enough to support the development of low pressure systems. This combination makes October one of the important months for cyclonic activity over the North Indian Ocean.
The Bay of Bengal does not suddenly become cyclone prone when September ends. The conditions that support these systems develop as the monsoon retreats. During the southwest monsoon, strong atmospheric circulation and wind shear generally make it difficult for tropical disturbances to organise into strong cyclones over the Bay. As the monsoon weakens and withdraws, these conditions change. October therefore marks the beginning of the post monsoon cyclone season, which extends through December.
One important change is the weakening of the southwest monsoon circulation. The monsoon trough, which is a major feature of the summer circulation over India, gradually shifts southward and weakens as the monsoon withdraws. At the same time, weather disturbances can develop over the Bay of Bengal and move westward or northwestward towards the eastern coast.
The sea itself is another important factor. Tropical cyclones require warm ocean water because evaporation supplies moisture to the atmosphere, while condensation of that moisture releases latent heat. This heat release can help a developing low pressure system strengthen when other atmospheric conditions are favourable.
October also has an important advantage for developing systems because atmospheric wind shear can become more favourable than it is during the active southwest monsoon. Strong vertical wind shear can disrupt the structure of a developing tropical system by displacing its convection from the circulation centre. Lower wind shear allows the circulation and thunderstorms to become better organised. Research on Bay of Bengal systems has found that wind shear plays an important role in whether post monsoon storms weaken or intensify.
This is why October frequently sees a sequence that begins with a low pressure area. If atmospheric and oceanic conditions remain favourable, a low pressure area can become a depression, then a deep depression and, if it strengthens further, a cyclonic storm. Not every low pressure system reaches cyclone intensity. The development of each system depends on the conditions surrounding it.This distinction is important this year as well.The system that recently affected Odisha and Andhra Pradesh was not officially a cyclone. It developed into a depression and then a deep depression. The name “Arnab” was being used in forecasts and reports because it was the next name on the regional naming list if the system reached cyclonic storm intensity. It did not officially reach that category before making landfall. Therefore, describing Arnab as a cyclone would be meteorologically incorrect.
There is also a possibility of another weather system developing in the Bay of Bengal during mid October 2026, but it is important not to describe it as an approaching cyclone at this stage. The India Meteorological Department’s extended range forecast issued on October 1 indicated the possibility of a cyclonic circulation over the North Andaman Sea around October 12, followed by the possible formation of a low pressure area. It also indicated a low probability of cyclogenesis over the central and adjoining south Bay of Bengal around October 15.
That means the present information supports the possibility of a low pressure system and potential development, not a confirmed cyclone approaching Odisha. The eventual intensity and track will depend on how the system actually develops and the atmospheric and oceanic conditions it encounters.
Odisha’s history shows why October receives particular attention.One of the most significant examples is the 1999 Odisha Super Cyclone, which made landfall on October 29 near Paradip. It remains one of the strongest cyclones to have affected Odisha and became a major turning point in the state’s disaster preparedness.In October 2013, Very Severe Cyclonic Storm Phailin developed over the Bay of Bengal. According to the India Meteorological Department, the system formed from a low pressure area over the North Andaman Sea on October 7, became a depression on October 8 and intensified into a cyclonic storm on October 9. It subsequently strengthened into a very severe cyclonic storm and crossed the Odisha coast near Gopalpur on October 12.
Five years later, Cyclone Titli affected Odisha in October 2018. It intensified over the Bay of Bengal before making landfall near the Odisha Andhra Pradesh border on October 11.More recently, Severe Cyclonic Storm Dana made landfall on the Odisha coast in the early hours of October 25, 2024, near Bhitarkanika and Dhamra. The storm produced strong winds and heavy rainfall across parts of Odisha and West Bengal.
October systems do not always make landfall in Odisha. In 2025, Cyclone Montha developed over the Bay of Bengal in late October and crossed the Andhra Pradesh coast, while southern Odisha also received heavy rainfall associated with the system.
These examples show the reason October remains closely watched along the Odisha coast. It is not because a cyclone forms every October, nor because every low pressure system becomes a cyclone. Rather, October brings together several seasonal conditions that can make the Bay of Bengal favourable for cyclonic development.For Odisha, the end of the rainy season therefore does not necessarily mean the end of weather-related risk. The transition from the southwest monsoon to the post monsoon season creates a new period in which low pressure systems and cyclones can develop over the Bay of Bengal. What begins as an ordinary area of disturbed weather can sometimes strengthen considerably, depending on the conditions over the sea and atmosphere.
