Northeast monsoon: Tamil Nadu's October-December rainy season
Why in news: On 12 October 2026, DD News reported a weather observer's forecast that the northeast monsoon may set in around 15 October.
The northeast monsoon is the October-December rainy season of south Peninsular India, which begins when winds turn northeasterly after the southwest monsoon withdraws. It covers five IMD subdivisions and gives Tamil Nadu about 48% of its yearly rain, per IMD Chennai. A weather observer expects onset around 15 October; IMD has not declared it.
Syllabus: Prelims · Geography; GS1 · Geophysical Phenomena; GS3 · Disaster Management
Why this matters for UPSC
GS1 geography and GS3 disaster management: Prelims asks which winds, subdivisions and ocean drivers shape the northeast monsoon; Mains asks why Tamil Nadu depends on it and how its cyclones are managed.
In short
The northeast monsoon is south Peninsular India's October-December rainy season, which IMD calls a small-scale monsoon; it begins when winds turn northeasterly after the southwest monsoon withdraws.
With Tamil Nadu's water and second crop riding on one cyclone-prone season, region-specific forecasts must guide both drought planning and evacuation.
Why it matters
Farmers across the five subdivisions depend on these rains for the region's second major crop season, and in Tamil Nadu they are the main rain of the year. A weak season leaves less water in reservoirs and groundwater for the dry months; IMD's 2026 outlook itself warns that below-normal rain in some areas could raise irrigation needs and cut recharge. A strong season carries a different risk: Bay of Bengal cyclones and very heavy rain flood coastal districts, as Cyclone Ditwah did over north Tamil Nadu and Puducherry in December 2025, per IMD Chennai. The season thus joins farm planning, water supply and disaster management in one forecast.
Prelims pointers
- The five subdivisions: Coastal Andhra Pradesh and Yanam; Rayalaseema; Tamil Nadu, Puducherry and Karaikal; South Interior Karnataka; Kerala and Mahe.
- Wind reversal: low-level winds turn from southwesterly to northeasterly after the southwest monsoon withdraws; the ITCZ shifts southward.
- Yanam lies in Andhra Pradesh, Karaikal in Tamil Nadu and Mahe in Kerala; all three belong to the Union Territory of Puducherry.
- The northeast monsoon also waters Sri Lanka, the Maldives and southern coastal Myanmar, per IMD.
- Favourable drivers, per IMD Chennai: El Nino, positive Indian Ocean Dipole, and Madden-Julian Oscillation in phases 2-4 with amplitude above one.
- IMD, under the Ministry of Earth Sciences, has issued the northeast monsoon outlook since 1998; normal means 88-112% of the long period average.
- Since 2010 IMD has led the South Asian Seasonal Climate Outlook Forum, supported by the World Meteorological Organization.
- October-December is the primary cyclone season of the North Indian Ocean: the Bay of Bengal and the Arabian Sea.
Practise a UPSC-style question
With reference to the northeast monsoon and Tamil Nadu, consider the following statements:
1. During the southwest monsoon, Tamil Nadu lies in the rain-shadow of the Eastern Ghats.
2. The Tamil Nadu, Puducherry and Karaikal subdivision normally receives nearly half of its annual rainfall in October-December.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Show the answer
Answer: (b) 2 only
1 is incorrect: Tamil Nadu lies in the rain-shadow of the Western Ghats, which block the moist southwest monsoon winds coming from the Arabian Sea. 2 is correct: IMD Chennai puts the subdivision's October-December share at about 48% of its annual rainfall, against about 47% in June-September.
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