Model Answer

Introduction

On October 16, 2025 the India Meteorological Department (IMD) announced the withdrawal of the southwest monsoon from the entire country and, simultaneously, the commencement of northeast monsoon rainfall activity over large parts of the southern peninsula (Tamil Nadu, Puducherry-Karaikal, Rayalaseema, south interior Karnataka, Kerala–Mahe and coastal Andhra Pradesh). This near-simultaneous transition—withdrawal of the SWM and onset of the NEM—has become noticeably frequent in recent years and deserves examination.

Body

1. Mechanism and meteorological factors

   • Change in large-scale wind pattern: The SWM withdraws when northeasterly/easterly winds start to prevail at low tropospheric levels over the southern peninsula, replacing the moist southwesterlies. The IMD noted easterly/northeasterly winds over southern India at the time of withdrawal.
   • Upper-air cyclonic circulation over the Comorin region: The IMD's bulletin for October 16, 2025 explicitly linked the simultaneous onset/withdrawal to an upper-air cyclonic circulation over the Comorin area which aided organised convection (rainfall) over Tamil Nadu, Kerala and adjoining regions — effectively bringing Bay of Bengal moisture into the peninsula and reinforcing easterly flows. Such circulations can produce post-monsoon spells even as the SWM withdraws.
   • Delayed/shifted timing of monsoon phases: The SWM’s retreat is normally completed by October 15; in 2025 the withdrawal was on October 16 (a one-day delay), while Kerala had seen an unusually early SWM onset on May 24. Variability in arrival and retreat dates increases the chance of overlap between withdrawal and NEM onset.
   • Role of synoptic systems and ENSO tendency: Formation of low-pressure/cyclonic systems in the Bay of Bengal or southeast Arabian Sea during October–December commonly trigger the NEM. The IMD also pointed to neutral ENSO with a rising possibility of La Niña conditions in coming months, which could favour an above-normal NEM in 2025 — reinforcing early post-monsoon activity.

2. Why simultaneous occurrence has been observed more often since 2020

   • Inter-annual variability: Years with early onsets or delayed retreats (or both) compress the seasonal window and increase overlaps. Since 2020 similar coincidences have been reported, indicating a pattern of larger seasonal shifts rather than isolated anomalies.
   • Changing frequency of synoptic events: Increased frequency/intensity of post-monsoon low-pressure systems or cyclonic circulations in the southern peninsula can produce NEM rainfall even before the SWM has fully withdrawn from certain pockets, causing apparent simultaneity.

3. Impacts and significance

   • Agriculture: Farmers in peninsular regions adjust sowing/harvesting and irrigation schedules according to monsoon phases. Overlap or unpredictability can disrupt harvest operations for late Kharif crops and delay timely sowing of Rabi or short-duration pulses that rely on post-monsoon rains.
   • Water resources & reservoirs: A strong NEM following an early withdrawal or simultaneous transition can help reservoir refill in the south; conversely, delayed or erratic withdrawal may complicate water planning for states dependent on predictable seasonality.
   • Disaster risk and urban flooding: Intensified spells associated with cyclonic circulations may bring heavy to very heavy rainfall in localized pockets (IMD advisories noted isolated heavy to very heavy falls over Tamil Nadu and Kerala). This raises flash-flood, landslide and urban drainage stress, calling for early warnings and preparedness.
   • Forecasting and advisories: Simultaneous transitions emphasize the need for high-resolution, short-range forecasting and timely dissemination to agriculture, fisheries and disaster management agencies (e.g., fishermen advisories for strong coastal winds).

4. Link with climate change

   • Attribution caution: While shifts in timing and increased variability are consistent with broader expectations under climate change (greater variability, changing storm tracks), direct attribution of one year's simultaneous onset/withdrawal to climate change requires formal attribution studies. Hence, policy and adaptation should be informed by observed trends and targeted climate-modelling studies rather than single events.
   • Need for resilience: Regardless of attribution, the observed variability argues for climate-resilient agricultural practices, improved water management, strengthening of early-warning systems and ground-level preparedness in southern peninsular states.

Conclusion/Way Forward

The simultaneous withdrawal of the southwest monsoon and onset of the northeast monsoon over southern India is primarily a manifestation of changing synoptic wind patterns – particularly easterlies aided by cyclonic circulations over the Comorin area – coupled with inter-annual shifts in monsoon timing. The phenomenon has important implications for agriculture, water management and disaster preparedness; policy responses should prioritise improved forecasting, climate-resilient planning and timely advisories for vulnerable sectors.