Cyclone Arnab made landfall on 28 October on the Andhra Pradesh and Yanam coasts as a very severe cyclonic storm, with flash flood warnings for 13 districts. An explainer links its fast intensification and its path to this year’s El Niño.

El Niño shifts where Bay of Bengal cyclones form and where they strike.

• Usual pattern: Odisha and West Bengal are the coasts most prone to Bay of Bengal cyclones.
• In El Niño years: Cyclones tend to form at lower latitudes, so they are more likely to move towards Andhra Pradesh and Tamil Nadu, as the IMD chief had explained. Cyclone Hudhud (2014), another El Niño year, hit the Andhra coast.
• Post-monsoon winds: After the monsoon withdraws in mid-October, the monsoon trough moves south. A warmer ocean under El Niño also changes wind and air pressure near the equator.

• Warm ocean: In July to September 2026, the sea surface temperature in the Niño 3.4 region was 2 to 2.8°C above normal. Ocean temperatures of 26°C or more at 50 to 100 metres depth help cyclones form, and Arnab reached its peak intensity in a single day.
• Other factors: Intensification also depends on wind shear, convection, upper ocean circulation and air-sea interaction.
• Speed: Cyclones formed in these conditions also move faster, as Arnab did.

• Normal pattern: A cyclone usually loses strength once it moves over land.
• Arnab: It kept its strength for at least six hours and stayed nearly stationary near Narsapur and Yanam from 4 am, which slowed the landfall process. Landfall normally takes up to six hours or more, depending on the cyclone’s speed and size.

• Forecasting rapid intensification: Arnab strengthened and moved faster than forecast.
• Inland flooding: Remnants of the cyclone can bring heavy rain far from the coast, as in Telangana, Bihar and east UP.
• Shifting risk: Andhra Pradesh and Tamil Nadu need to prepare more in El Niño years.
• Coastal geography: The Bay of Bengal is funnel-shaped, landlocked on three sides and shallow near the coast, so it is prone to storm surges.

• Arnab: Named by Bangladesh. Next names are Murasu (India, Tamil for drum) & Akvan (Iran).
• Naming: The WMO/ESCAP Panel on Tropical Cyclones (13 members) began naming in September 2004. A list of 169 names was adopted in April 2020.
• Landfall: When the cyclone’s eye crosses the coast. Yanam is a Puducherry enclave on the Andhra coast.
• Formation needs: Sea surface of about 26 to 27°C or more, low wind shear, moist air, the Coriolis force and an existing disturbance.
• Season: October to December is the main cyclone season in the Bay of Bengal.