El Niño and Tamil Nadu’s Northeast Monsoon

Context: Why in News?

A strong El Niño generally weakens India’s southwest monsoon, but it can intensify rainfall over Tamil Nadu during the northeast monsoon season from October to December. Warm waters in the Bay of Bengal and regional atmospheric circulation can produce rainfall patterns in Tamil Nadu that differ considerably from the overall national trend.

Key Highlights

• El Niño and atmospheric circulation: El Niño refers to the abnormal warming of the central and eastern equatorial Pacific Ocean, which alters the Walker circulation and influences global weather patterns.
• Importance of the northeast monsoon: Unlike most parts of India, Tamil Nadu receives a substantial proportion of its annual rainfall from the northeast monsoon.
• Role of pressure differences: Atmospheric pressure differences between the Bay of Bengal and the Arabian Sea can direct moisture-laden winds towards the coastal regions of Tamil Nadu.
• Influence of warm ocean waters: Higher sea surface temperatures increase evaporation and provide additional energy and moisture to low pressure systems and cyclones.
• Bay of Bengal warming: In September 2026, sea surface temperatures in the southern Bay of Bengal were reported to be approximately 1°C above normal.
• East India Coastal Current: This current undergoes seasonal reversals and influences coastal water transport and sea surface temperatures.
• Heat retention in the Bay of Bengal: A shallow mixed layer and salinity stratification help retain heat near the ocean surface, influencing ocean atmosphere interactions.
• Indian Ocean Dipole: The Indian Ocean Dipole also influences regional climate and rainfall patterns through differences in sea-surface temperatures across the equatorial Indian Ocean.
• Coastal preparedness: As the likelihood of intense weather events increases, coastal communities require timely warnings, preparedness measures and adequate support. Continuous ocean monitoring is essential for improving forecasts.

Key Concepts

• Indian Ocean Dipole (IOD): A climate phenomenon characterised by differences in sea surface temperatures between the western and eastern equatorial Indian Ocean.
• Mixed Layer: The upper layer of the ocean where temperature and salinity remain relatively uniform due to mixing.
• Ocean Atmosphere Coupling: The two way interaction between the ocean and atmosphere through the exchange of heat, moisture and momentum, influencing weather and climate patterns.

Way Forward

Forecasting should move beyond broad seasonal predictions towards district-level assessments of potential impacts on reservoirs, urban flooding, fisheries, agriculture and evacuation requirements. Expanding the use of ocean monitoring buoys, radars, gliders and real-time observation systems can improve forecasting capabilities. Forecast uncertainty should also be communicated clearly to support effective disaster preparedness and protect vulnerable coastal communities.