Source: ITV
Subject: Geography
Context: Cyclone Ditwah has formed over the southwest Bay of Bengal and is moving towards Tamil Nadu, Andhra Pradesh and Puducherry.
- Around the same time, a separate system in the Strait of Malacca intensified into Cyclone Senyar, triggering very heavy rain over parts of Andaman & Nicobar Islands and South India.
About Cyclone Ditwah and Cyclone Senyar:
About Cyclone Ditwah:
- What it is & where formed:
- Cyclone Ditwah is a tropical cyclonic storm that formed over the southwest Bay of Bengal, rapidly intensifying from a depression to a cyclonic storm in less than 24 hours.
- It is Yemen’s recommended name.
About Cyclone Senyar:
- What it is & where formed:
- Cyclone Senyar originated from a low-pressure system near Malaysia/Strait of Malacca over the South Andaman Sea and adjoining region of Bay of Bengal, which intensified into a depression and further strengthened.
- It is UAE’s recommended name.
- Current status: Senyar later weakened over the Strait of Malacca, but the moisture and remnant circulation helped feed ongoing rain systems over South India and the Bay.
Why More Cyclones Form in Bay of Bengal During Retreating Southwest Monsoon?
- Very Warm Sea Surface Temperatures (SSTs)
- The Bay of Bengal retains high SSTs (~28–30°C or more) after the summer monsoon, providing huge latent heat, which is the primary fuel for cyclogenesis in October–November.
- High Moisture & Humidity:
- Abundant moisture inflow from equatorial Indian Ocean and Bay creates a deep, humid troposphere, favourable for strong convection and low-pressure formation.
- Shift of ITCZ & Monsoon Trough:
- The Inter-Tropical Convergence Zone (ITCZ) and monsoon trough shift southwards over the Bay in the retreating phase, creating a preferred zone of convergence and vorticity for cyclones.
- Low Vertical Wind Shear:
- In October–early November, upper-level winds become comparatively less hostile over the Bay, with reduced vertical wind shear, allowing nascent systems to organise into depressions and cyclones.
- Remnant Monsoon Lows Re-intensify:
- Monsoon depressions and lows moving from land back over the warm Bay waters during withdrawal often re-intensify into deep depressions/cyclones, especially in central and southwest Bay.
- Bay of Bengal vs Arabian Sea Contrast:
- The Bay is smaller, semi-enclosed and receives large river inflows (Ganga–Brahmaputra, etc.), maintaining warmer, stratified surface waters compared to the Arabian Sea, making it more cyclone-prone in this season.
