Cyclone Arnab: Role of El Niño in Its Path and Intensity

31 Oct 2026

Tags: Geography   Physical Geography   Climatology

Source: The Indian Express

Context: The first cyclone of 2026 in the North Indian Ocean basin (Bay of Bengal and Arabian Sea), it originated as a low-pressure system over the southeast Bay of Bengal on October 23 and intensified into a cyclone by October 26.

• Landfall: It crossed the coast between Bapatla and Visakhapatnam on October 28 as a very severe cyclonic storm, with sustained wind speeds of 125–135 km/h and gusts up to 140 km/h. It subsequently weakened into a severe cyclonic storm.
• Disaster impact: Over 1.8 lakh people were evacuated in Andhra Pradesh and Odisha. Heavy rainfall, flash-flood risks and damage to coastal infrastructure were reported.

Intensification and Movement of Cyclone Arnab

• Rapid intensification: Arnab strengthened quickly into a very severe cyclonic storm, challenging weather forecasting models. The IMD advanced its landfall forecast to the early hours of October 28, with landfall beginning around 1 a.m.
• Prolonged landfall: The cyclone remained nearly stationary near Narsapur in Andhra Pradesh and Yanam in Puducherry from around 4 a.m., prolonging the landfall process. It retained its intensity for approximately six hours after landfall before weakening.
• Rainfall impact: Significant rainfall was recorded at Visakhapatnam (217 mm), Kalingapatnam (147 mm), Tuni (123 mm), Kakinada (118 mm), Machilipatnam (115 mm) and Gopalpur (94 mm).
• Continuing rainfall threat: Heavy rainfall was expected along northern Andhra Pradesh and southern Odisha, followed by very heavy rainfall in parts of Telangana, Chhattisgarh, Jharkhand, Bihar, Gangetic West Bengal, eastern Madhya Pradesh and eastern Uttar Pradesh as the system moved inland.

Role of El Niño in Cyclone Formation and Track

• El Niño: A climate phenomenon characterised by abnormal warming of surface waters in the central and eastern equatorial Pacific Ocean. It alters atmospheric circulation, rainfall patterns and wind systems globally.
• Influence on cyclone tracks: According to IMD chief Mrutyunjay Mohapatra, during El Niño years, North Indian Ocean cyclones tend to form at lower latitudes and are more likely to move towards the Andhra Pradesh and Tamil Nadu coasts, rather than Odisha and West Bengal.
• Atmospheric circulation: After the southwest monsoon withdraws, winds weaken and the monsoon trough shifts southwards. El Niño-related changes in ocean temperatures, winds and atmospheric pressure can influence the location of cyclone formation and subsequent movement.
• Rapid intensification: Warm ocean waters provide energy to tropical cyclones. The Niño 3.4 region recorded sea-surface temperatures around 2–2.8°C above normal during July–September 2026, indicating strong warming in the equatorial Pacific. However, El Niño alone does not determine cyclone intensity or trajectory.

Why the Bay of Bengal Is Vulnerable to Cyclones

• Geographical factors: The Bay of Bengal is enclosed by land on three sides and has a funnel-like shape, which can amplify storm surges and increase coastal inundation risks.
• Warm ocean waters: Sea-surface temperatures of around 26°C or higher, along with sufficient warm water at depth, favour tropical cyclone formation and intensification.
• Cyclone movement: Tropical cyclones in the Northern Hemisphere are influenced by prevailing winds and large-scale atmospheric circulation, often moving westward or northwestward and affecting India’s eastern coast.

Factors Determining Cyclone Intensity

• Ocean heat content: Warm water supplies latent heat energy that fuels cyclone development.
• Vertical wind shear: Strong changes in wind speed or direction with height can disrupt cyclone structure and inhibit intensification.
• Convection and air–sea interaction: Moisture availability, thunderstorm activity, atmospheric boundary-layer conditions and upper-ocean circulation influence cyclone strength.
• Land interaction: After landfall, friction and reduced access to oceanic moisture generally weaken cyclones, although weakening may be delayed when a storm retains favourable atmospheric conditions.

Cyclone Classification and Naming

• Classification by wind speed: A severe cyclonic storm has wind speeds of 89–118 km/h, while a very severe cyclonic storm has wind speeds of 119–221 km/h.
• Naming mechanism: The Regional Specialised Meteorological Centre (RSMC), New Delhi, under the IMD, assigns names to qualifying cyclonic storms in the North Indian Ocean basin.
• Member countries: The 13 participating countries are Bangladesh, India, the Maldives, Myanmar, Oman, Pakistan, Sri Lanka, Thailand, Iran, Qatar, Saudi Arabia, the UAE and Yemen.
• Naming procedure: Countries submit names that must be short, easy to pronounce and inoffensive. Names are used sequentially and are not repeated once used. Arnab was proposed by Bangladesh, while the next name in the sequence is Murasu, proposed by India.