The rapid succession of Cyclone Arnab and Cyclone Murasu along the Bengal-Andhra coast has highlighted a difficult problem for coastal cities: the systems that usually suppress a second cyclone after a major storm did not prevent another one from developing within less than a week. Times of India reported that Arnab struck the Andhra coast on October 28, while Murasu was expected to make landfall between Monday midnight and Tuesday morning. Weather scientists described the sequence as a rare climatological anomaly.
The significance of the event lies not only in the two names appearing close together on a weather map. A cyclone changes the ocean and atmosphere around it. Its winds churn the upper layers of the sea, bring colder water to the surface and disturb the pressure, moisture and wind fields needed for another storm to form. A second system developing soon afterwards therefore has to overcome conditions that have temporarily become less favourable for cyclogenesis.
The report explains tropical cyclones as large atmospheric heat engines. For a cyclone to form and intensify, the sea surface must be sufficiently warm, with the heat extending down through several tens of metres of water. The article cites a minimum sea-surface temperature of 26.5°C as a requirement. When a powerful storm moves slowly over the Bay of Bengal, its winds can draw colder water upwards from below. This creates what scientists call a cold wake, reducing the heat available to a following system.
That mechanism normally creates a natural gap between successive storms. The sea needs time to regain heat, while the atmosphere also needs to recover from the first cyclone’s influence. In the case of Arnab and Murasu, however, the two systems originated in different parts of the Bay. Arnab formed over the east-central Bay, while Murasu developed over the south-east Bay. HR Biswas, deputy director-general of meteorology, told the newspaper that conditions in the two areas were different and that a storm in one part of the central Bay may not significantly alter conditions elsewhere.
This geographic separation is important for understanding why the second system could develop so quickly. The Bay of Bengal is not a single, uniform weather environment. Different parts of the basin can have different ocean temperatures, moisture conditions and wind patterns at the same time. A storm’s strongest impact on the upper ocean may therefore remain concentrated around its own track, leaving another region with enough available energy for a new disturbance.
The atmosphere usually presents another barrier. A mature cyclone draws in large quantities of moisture and heat, while releasing latent heat high into the atmosphere. According to the senior weather scientist quoted in the report, this process changes regional pressure patterns and produces subsidence, or sinking air, around the storm. Sinking air suppresses thunderstorm formation and creates a temporary period in which the atmosphere is less likely to generate a new low-pressure core.
A cyclone can also disrupt the wind structure needed by a second storm. Tropical systems require low vertical wind shear, meaning that winds near the surface and higher in the atmosphere must remain relatively similar in speed and direction. Strong differences between those levels can tilt or break apart a developing vortex. The trailing circulation of a previous cyclone can leave behind high wind shear or upper-level disturbances that interfere with a new system.
The reported sequence suggests that these suppressing effects were either weaker, more localised or offset by conditions in the region where Murasu formed. Meteorologists quoted by Times of India referred to an ‘over-energised’ Bay of Bengal. Their explanation was that heat accumulated across the basin during the summer and remained available late in the post-monsoon season. Even after one storm brought cooler water upwards, the wider basin may have retained enough background heat to support another cyclone.
This does not mean that every warm Bay of Bengal season will produce consecutive cyclones. The report presents the Arnab-Murasu sequence as rare precisely because several conditions have to coincide. There must be sufficient ocean heat, a suitable atmospheric circulation, low enough wind shear and a location where the first storm does not substantially exhaust the energy available to the second. The unusual feature is the combination and timing, not simply the existence of two cyclones in one season.
The region has experienced closely spaced systems before, but the comparison also reinforces the exceptional timing of the present event. The report refers to the 2013 season, when Cyclone Phailin made a severe landfall in Odisha in October and was followed by systems including Helen and Lehar over the following weeks. It also mentions the late-2020 season, when Nivar and Burevi occurred in a highly active period but were separated by a somewhat longer interval. Arnab and Murasu were reported to have affected the same broad Bengal-Odisha-Andhra coastal stretch within less than seven days.
For coastal urban systems, the administrative challenge in such a sequence is the compression of recovery and preparedness into the same operational window. A first cyclone can affect roads, electricity networks, drainage, communications, housing and public facilities. If another system approaches before those services have fully recovered, agencies may have to conduct response, repair and evacuation operations simultaneously. The supplied report does not provide damage figures or details of municipal deployment, but the weather pattern itself reduces the time available between alerts and successive emergency actions.
The urban risk is also shaped by the geography of the east coast. The storm origins described in the report are offshore, while the expected landfall zone extends across a densely settled coastal region linked by transport, fishing, industrial and agricultural activity. A cyclone does not need to strike the same city twice to create a compound governance problem. Disruptions in one coastal district can affect movement, supply chains and emergency capacity in neighbouring areas, particularly when weather systems arrive in rapid succession.
The episode also demonstrates why cyclone preparedness cannot rely only on the intensity of an individual storm. Municipal and state authorities need to account for the time between events, the condition of infrastructure after the first impact and the possibility that a second system may develop in a different part of the Bay. The report does not identify a specific policy change or preparedness failure, so it cannot establish how authorities responded or whether existing plans were adequate. It does, however, show why sequential-event planning is distinct from preparing for a single cyclone.
The central evidence remains meteorological rather than administrative. Arnab struck the Andhra coast on October 28, Murasu formed in a different part of the Bay and was expected to make landfall within the following week. Scientists cited the unusually warm background conditions of the basin, the separation between the systems’ areas of origin and the atmospheric mechanisms that typically inhibit rapid secondary cyclogenesis. Together, these facts explain why the sequence was treated as an anomaly.
What remains uncertain from the supplied material is the eventual intensity and impact of Murasu, the precise damage caused by either storm and whether the event represents a broader shift in cyclone behaviour. The report supports a narrower conclusion: the Bay of Bengal can, under specific conditions, sustain closely timed systems even after the first cyclone has disturbed the ocean and atmosphere. For coastal cities, that possibility makes the interval between storms as important as the storm forecast itself.
