Why is the east coast of India more prone to tropical cyclones than the west coast? Explain the post-monsoon (October–December) cyclone season.

India's east coast faces far more tropical cyclones than its west coast. Between 1891 and 1990, about 262 cyclones struck a 50-km strip along the east coast, against 33 on the west coast [1]. The cause is both oceanic and geographical, and the risk is highest in the post-monsoon months.

Why the east coast is more prone

• More systems form in the Bay: the Bay of Bengal produces roughly four times as many cyclones as the Arabian Sea [1]. In October–December 1971–2020 it produced 168 depressions against 62 in the Arabian Sea [2].
• Warm, low-salinity surface water: freshwater from the Ganga–Brahmaputra stays on top and keeps the surface warm, which feeds convection.
• Pacific remnants: typhoon remnants from the South China Sea often regenerate over the Bay.
• Storms head for the coast: 81.5% of Bay systems cross the coast, against 32.3% for the Arabian Sea, where most dissipate at sea [2].
• Funnel-shaped Bay, shallow shelf, flat deltas (Krishna–Godavari, Mahanadi): these amplify storm surge, the main cause of cyclone deaths [1].
• West coast is sheltered: the Arabian Sea is cooler, and its storms usually track west or northwest, away from India.

The post-monsoon (October–December) season

• Trigger: the SW monsoon withdraws and northeasterly winds set in over the Bay [3]. The monsoon trough moves south over warm water, and vertical wind shear is low during this changeover.
• Systems form further south as the season goes on: depressions form at about 13.9°N in October and about 7.7°N in December [2]. Landfall therefore moves from Odisha and Andhra Pradesh to Tamil Nadu and Sri Lanka.

Oct: ~13.9°N → Odisha/AP   |   Nov: ~11.1°N → AP/TN   |   Dec: ~7.7°N → TN/Sri Lanka

Southward shift of where depressions form, Oct–Dec [2]

• Paths are hard to predict: in October 1976 a storm expected to hit Madras turned north to Masulipatnam. Madras still received 344 mm in four days [4].
• Mixed effect on rainfall: Tamil Nadu gets 48.1% of its annual rain in October–December [2], so these systems matter. But a storm can also pull moisture away: VSCS Hamoon (2023) cut Tamil Nadu's rainfall [5].

To sum up, warm seas, more systems forming and storms that head for the coast make the east coast India's main cyclone zone, and October–December is its peak season. IMD's day-wise forecasts [3] should be backed by surge-resilient shelters and last-mile warnings, in line with the Sendai Framework and SDG 11.