Why are October–November cyclones in the Bay of Bengal more frequent and more damaging than Arabian Sea cyclones?

Every year the North Indian Ocean sees about 5–6 tropical cyclones. About 4 form in the Bay of Bengal (BoB) and only 1 in the Arabian Sea, and the BoB's peak comes in October–November [1]. The BoB has two advantages. Its ocean and atmosphere favour cyclone formation, and its coasts turn that frequency into heavy losses.

Why BoB cyclones are more frequent

• Warmer sea surface: the Bay has warm, less saline waters. The western Arabian Sea is colder, so fewer systems form there and more of them die out [1].
• Pacific "seedlings": many low-pressure systems that start BoB cyclones are the remains of West Pacific typhoons. They drift west through the South China Sea and Gulf of Thailand and strengthen again over the Bay [1].
• Post-monsoon conditions: in November, the chance of a depression growing into a cyclonic storm is about 69%, among the highest in the year [1].
• Arabian Sea systems fade: about 50% of Arabian Sea cyclones dissipate over the sea. Many others turn north beyond 15°N towards Gujarat [1].

Why BoB cyclones are more damaging

• High landfall rate: over 60% of BoB cyclones hit India's east coast and about 30% hit Bangladesh–Myanmar. Only about 10% die out at sea [1].
• Storm-surge geography: the Bay has a shallow continental shelf and a funnel-shaped head. Together they pile seawater onto the low-lying Ganga–Brahmaputra, Mahanadi and Godavari–Krishna deltas.
• Exposed populations: the 1970 Bangladesh cyclone killed over 3,00,000 people. The Odisha Super Cyclone (29–30 October 1999) killed over 10,000 people. With a very severe cyclonic storm 11 days earlier, it caused more than $2.5 billion in damage [1].
• Repeated rain hits on Tamil Nadu: Fengal crossed near Puducherry in November 2024 and brought extremely heavy rain [2]. In November 2025, a deep depression off Sri Lanka threatened Tamil Nadu while Senyar was still over the Strait of Malacca [3]. Ditwah then caused widespread damage in north Tamil Nadu [4].
• Hidden extremes: Tamil Nadu's 2025 season was rated "Normal". Yet it still had 7 days of extremely heavy rain [4].

In short, warm seas, Pacific remnants and a peak in November make BoB cyclones more frequent. A high landfall rate, the surge-prone funnel shape of the Bay and crowded deltas make them more deadly. The way forward is to expand impact-based warnings, use the aircraft reconnaissance proposed under FDP-BOBTEX [1], and restore mangroves and cyclone shelters. These steps would help India move from counting deaths to "zero casualty" preparedness, in line with the Sendai Framework and SDG 13.