Weather Alert: Deep Depression Over Bay of Bengal Triggers Heavy Rainfall Warning for West Bengal

By Editorial Desk | Updated: September 21, 2026, 04:20 AM IST

Executive Summary: The Impending Weather System

The India Meteorological Department (IMD) has issued a high-alert warning for West Bengal as a potent weather system develops over the Bay of Bengal. A low-pressure area, currently situated over the east-central Bay of Bengal and the adjoining north Andaman Sea, is projected to intensify into a formal depression by Monday, September 21, 2026. This system is expected to trigger a multi-day spell of adverse weather, characterized by heavy rainfall, squally winds, and potential tidal surges, affecting the state from September 22 through September 26.

Meteorologists have characterized the system as a "deep depression" in its projected trajectory, which poses a significant threat to coastal infrastructure and agricultural activities. Residents across both southern and northern districts of West Bengal are urged to prepare for disruption as the state braces for what could be a week of intense meteorological activity.

Chronology of the Meteorological Event

The development of this weather pattern has been monitored closely by satellite imagery and oceanic sensors.

• September 20-21: The system originated as a low-pressure area over the Andaman Sea. IMD bulletins confirm that the system is tracking west-northwestwards. By the morning of September 21, the convergence of moisture and wind shear began to organize the system, leading to the official forecast of it becoming a depression.
• September 22: The system is expected to exert its primary influence on the West Bengal coastline. Coastal districts should anticipate the onset of heavy precipitation and gusty winds reaching speeds of 40–50 kmph.
• September 23: The core of the system is projected to move toward the west-central and northwest Bay of Bengal, positioning itself near the north Andhra Pradesh and South Odisha coasts. Simultaneously, the sub-Himalayan regions of West Bengal—including Darjeeling, Kalimpong, and Jalpaiguri—will begin to experience the secondary effects of the system, with heavy rainfall forecasted for these higher-altitude districts.
• September 24–25: The peak period of the weather event. The IMD expects continued heavy rain across both the southern plains and the northern mountainous regions.
• September 26: A gradual weakening of the system is anticipated, though residual moisture and localized flooding remain a concern as the system dissipates.

Regional Impact and Supporting Data

The geographical spread of this depression is extensive, covering nearly the entire state of West Bengal. The IMD has provided granular details regarding the expected impact:

The Coastal Corridor

The districts of Purba Medinipur and South 24 Parganas are currently at the highest level of risk. Meteorological models suggest these regions will bear the brunt of the storm, with wind speeds expected to fluctuate between 40 and 50 kmph. These conditions present a high risk for uprooting trees, damage to semi-permanent housing structures, and disruption to local power grids.

South Bengal and Kolkata

While the center of the storm tracks toward the Odisha-Andhra coast, the periphery will impact Kolkata and surrounding southern districts. The IMD predicts thunderstorms accompanied by lightning and gusty winds of 30–40 kmph. Urban centers must remain vigilant against waterlogging, particularly in low-lying areas where drainage systems may be overwhelmed by heavy precipitation.

Sub-Himalayan and North Bengal

The weather disturbance is not limited to the coast. Starting September 23, the northern districts of Darjeeling, Kalimpong, Jalpaiguri, Alipurduar, and Cooch Behar are under a heavy rain alert. These regions are particularly sensitive to high-intensity rainfall, which often triggers landslides and flash floods in the hilly terrain. Districts such as Uttar Dinajpur, Dakshin Dinajpur, and Malda will also face convective weather, including thunderstorms and localized squalls.

Official Directives and Safety Protocols

The IMD has moved to prevent loss of life and property through a series of stringent advisories directed at the maritime and coastal communities.

Maritime Restrictions

The most critical directive concerns the fishing community. The IMD has explicitly advised fishermen to avoid venturing into the deep sea from September 21 onward. Those currently at sea are mandated to return to the coast by the night of September 21. The deep-sea conditions are expected to become increasingly treacherous, with wave heights and swell frequencies making navigation hazardous.

Wave Dynamics

The IMD has issued a specific warning regarding "swell waves." Forecasts indicate waves with a 16.0–19.0-second period and heights ranging from 0.9 to 1.1 meters. This, combined with the storm’s pressure, creates a high possibility of "surging waves." Authorities have warned that boats should ply with "utmost vigilance," and coastal recreation—such as beach visits or water sports—is strongly discouraged during this window.

Socio-Economic Implications

The arrival of this depression at the tail end of September holds significant implications for West Bengal’s economy, particularly in the agricultural sector.

Agricultural Vulnerability:
Much of West Bengal’s agricultural output, particularly the late-season paddy crop, is susceptible to heavy rainfall and wind-induced lodging. Prolonged waterlogging in the southern plains could lead to crop rot, while landslides in the northern tea-growing regions could disrupt the supply chain and damage plantation infrastructure.

Infrastructure and Urban Planning:
For cities like Kolkata, the forecast serves as a stress test for existing urban infrastructure. With climate change intensifying the frequency of Bay of Bengal depressions, the reliance on aged drainage systems is a growing concern. Local municipal bodies are expected to activate disaster management cells to clear drains and ensure that pumping stations are operational to mitigate the risk of flooding.

Tourism and Transport:
The alert coincides with a period where the northern hill districts typically see a surge in tourism. Authorities have warned travelers to exercise extreme caution when navigating the hilly roads of Darjeeling and Kalimpong, as heavy rain often leads to road blockages due to rockfalls and debris. Air and rail travel may also face delays, and commuters are advised to monitor official updates closely before planning travel during the peak window of September 23–25.

Conclusion: A Call for Vigilance

As West Bengal enters this period of intense meteorological instability, the synergy between official forecasting and public preparedness is paramount. The IMD’s early warning system provides a crucial buffer, allowing state authorities and the public to take preventative measures.

While the "deep depression" is currently tracked to move toward the Odisha-Andhra coast, the sheer scale of the moisture influx ensures that West Bengal will remain a primary theater for this weather event. Whether through the risk of coastal inundation in the South or the threat of landslides in the North, the state is facing a comprehensive challenge.

Residents are urged to stay tuned to local radio, television, and government weather portals. In times of severe weather, the difference between minor inconvenience and disaster often comes down to the speed and accuracy of one’s response to official advisories. As the system intensifies on September 21, the focus shifts from monitoring to active management of the risks posed by this significant Bay of Bengal depression.