Abdul Wahab Khan
Panaji
Once known for its relative calm, the Arabian Sea is now showing a rise in cyclonic activity during the post-monsoon season between October and December, even as the Bay of Bengal continues to dominate the subcontinent’s storm map, an analysis of long-term IMD records has shown.
According to historical data from the India Meteorological Department (IMD) of 133 year covering the period 1891 to 2024, the Arabian Sea has witnessed a gradual but steady increase in cyclonic disturbances—including depressions and storms—particularly in recent decades.
Between 1891 and 2024, the Arabian Sea recorded 112 cyclonic disturbances (depressions and above) during the October–December period, while the Bay of Bengal generated a commanding 465 systems—over four times higher, accounting for nearly 70 per cent of all cyclonic disturbances in the North Indian Ocean basin. The land surface of India saw just 10 systems over the same period, mostly as weakened remnants of oceanic storms.
Month-wise, the Bay of Bengal remained most active in October (199 disturbances) and November (176), with a decline in December (90) as sea surface temperatures cool. The Arabian Sea, by comparison, shows 53 disturbances in October, 43 in November, and 16 in December.
A cyclonic depression is the earliest organised stage of a tropical storm, formed when a low-pressure area over warm ocean waters draws in moist air, leading to convective activity and strong winds between 31 and 50 km/h. If the system strengthens and winds exceed 62 km/h, it becomes a cyclonic storm. The Arabian Sea, once used to have dry air from the Arabian Peninsula, now exhibits warmer and more humid conditions—ideal for storm genesis.
Statistically, 85 per cent of all post-monsoon cyclonic activity occurs in October and November, making them the most volatile months for India’s east and west coasts alike. While the Bay of Bengal remains India’s primary cyclone generator, the Arabian Sea’s share of total systems has risen from about 12 per cent in the early 20th century to nearly 24 per cent in recent decades, signalling a profound regional transformation.
The Arabian Sea has seen several intense cyclones in the last decade—such as Mekunu (2018), Kyarr (2019), and Tauktae (2021)—each leaving a deep imprint on India’s western coast.
An analysis of long-term IMD records reveals distinct century-wise trends.
From 1891 to 1950, the Arabian Sea averaged just 0.6 cyclonic disturbances per year—roughly one every 1.6 years, totalling 36 systems in six decades often dissipating before reaching the Indian coastline. In the following half-century (1951-2000), the average rose modestly to 0.8 systems per year, or about one every 1.25 years, corresponding to 40 systems.
IMD scientists have noted that the number of cyclonic systems may be stable or declining, but their intensity and unpredictability have increased.
“The Arabian Sea is no longer the quiet basin it once was,” said a senior IMD meteorologist. “We’re witnessing the ocean responds directly to climate change.”
However, the most dramatic surge came in the 21st century (2001-2024), when the Arabian Sea produced 36 disturbances in just 24 years, averaging 1.5 systems per year—a 90 per cent increase over the previous period and a 150 per cent rise from the early 20th century.
This means the basin now spawns one post-monsoon system roughly every eight months, compared to one every 18 months a century ago.
By comparison, the Bay of Bengal’s cyclone frequency has declined slightly over time—from an average of 3.8 disturbances per season (1891-1950) to 3.2 (1951-2000), and 2.8 (2001-2024)—even as its storms have grown more intense and destructive such as Phailin (2013), Titli (2018), and Amphan (2020). This reflects a global trend: fewer but stronger tropical systems, consistent with climate change projections.
