Kolkata Weather Alert: Thunderstorms Hit Today

Kolkata Weather Alert: Thunderstorms Hit Today

On September 20, 2025, Kolkata, the pulsating heart of West Bengal, awoke to a dramatic meteorological shift as the India Meteorological Department (IMD) issued a severe weather alert for thunderstorms and heavy rainfall across the city and surrounding districts. The warning, classified as an orange alert—indicating "be prepared" for disruptive conditions—forecasts intense downpours accompanied by lightning, gusty winds up to 40-50 km/h, and potential waterlogging in low-lying areas. With temperatures expected to range from a sticky low of 26°C to a humid high of 33°C, the alert comes at the tail end of an unusually prolonged monsoon season that has already drenched the region with 290 mm of rain in September alone, 15% above the long-term average.

Kolkata, home to over 14 million residents and a UNESCO Creative City of Music, is no stranger to the monsoon’s fury, but today’s alert signals a particularly volatile episode. The IMD's Regional Meteorological Centre in Alipore, drawing from INSAT-3D satellite data and Doppler radar feeds, predicts 70-150 mm of rainfall over 24 hours, with thunderstorms likely between 2 PM and 6 PM IST. This follows a week of erratic patterns: Light drizzles on September 16 (12 mm) escalated to heavy bursts on the 17th (45 mm), and scattered showers on the 18th (20 mm), per the department's daily bulletins. As #KolkataStorm trends on X with over 50,000 mentions by midday, residents from Howrah to Salt Lake are battening down—umbrellas at the ready, traffic apps buzzing, and markets like New Market opting for early closures. This comprehensive guide, based on IMD forecasts, historical trends, and local impact assessments, unpacks the alert's science, hourly breakdowns, safety measures, economic ripples, and cultural context. In a city where rain dances with resilience, today's thunderstorms aren't just weather—they're a test of Kolkata's indomitable spirit.

The Meteorological Mechanics: Monsoon Trough and Convective Chaos

Kolkata's weather in mid-September is a classic monsoon crescendo, where the southwest winds' retreat collides with lingering moisture from the Bay of Bengal. The IMD's orange alert stems from a southward-dipping monsoon trough—a low-pressure belt stretching from Jharkhand to coastal Karnataka—interacting with an upper-air cyclonic circulation over Gangetic West Bengal. This setup, detailed in the September 19 morning bulletin, funnels humid easterlies (85-90% relative humidity) into the city, triggering convective clouds that build to cumulonimbus towers reaching 12-14 km. Satellite imagery from INSAT-3D reveals these "thunder factories" forming over the Sundarbans mangroves, migrating northward to batter Kolkata with isolated heavy falls.

Thunderstorms, the alert's hallmark, arise from atmospheric instability: Convective Available Potential Energy (CAPE) values exceeding 1,500 J/kg signal explosive updrafts, separating electrical charges to produce lightning—potentially 10-20 strikes per hour in hotspots like Rajarhat and Behala. Winds from these cells could gust to 50 km/h, uprooting billboards or felled trees along Eastern Metropolitan Bypass. Rainfall intensity—20-40 mm per hour during peaks—exceeds the city's drainage capacity of 50 mm/hour, per Kolkata Municipal Corporation (KMC) specs, risking flash floods in underpasses like the one at Park Circus.

This isn't anomalous; September averages 290 mm over 20 rainy days, with thunderstorms on 12-15 occasions, per IMD's 30-year climatology. Climate models from IITM (2024 study) attribute a 20% increase in such events to warming Bay waters, amplifying convection. Today's alert echoes September 17's 45 mm deluge, which caused knee-deep flooding at VIP Road, but with added lightning risks—NDMA reports 2,000 annual lightning deaths in India, 10% in West Bengal. As the trough lingers, expect a 70% rain probability, cooling the "feels like" from 38°C to 30°C—a brief mercy in the muggy embrace.

Hourly Forecast Breakdown: Navigating the Storm's Rhythm

IMD's granular forecast for September 20 paints a volatile canvas, with rain probability peaking at 80% from afternoon to evening. Sunrise at 5:38 AM IST ushers partly cloudy skies with mist over the Hooghly, temperatures climbing to 29°C by 10 AM amid 90% humidity. The first rumbles arrive around 11 AM, light to moderate (5-10 mm/hour), but intensity builds post-noon.

• Morning Phase (6 AM - 12 PM): Overcast with patchy drizzle (2-5 mm total), low of 26°C. Winds southeast at 10-15 km/h, visibility 6-8 km. Ideal for indoor pursuits like a Victoria Memorial stroll, but thunder possible by 11 AM over Dum Dum airport.
• Afternoon Onslaught (12 PM - 6 PM): Peak chaos—heavy showers (20-40 mm/hour) with thunderstorms every 5-10 minutes, high of 33°C feeling 37°C. Gusts to 50 km/h risk disruptions at Park Street; lightning hotspots in Bidhannagar. Total accumulation: 50-100 mm.
• Evening Taper (6 PM - 12 AM): Moderate rain (10-20 mm) easing by 9 PM, low of 26°C. Winds drop to 8 km/h, skies clearing partially. Night owls at Science City may dodge the worst, but residual puddles linger.

AccuWeather's hyperlocal model aligns, forecasting 75 mm total—above September's 65 mm norm—with 85% thunderstorm chance. Isolated very heavy falls (>115 mm) could hit Howrah, per IMD's district bulletin. For air quality, rain flushes PM2.5 from 85 (moderate) to 45 (good), a silver lining for asthmatics in Ballygunge.

Immediate Impacts: From Traffic Snarls to Urban Flooding

Kolkata's infrastructure, a patchwork of colonial drains and modern sprawl, strains under such deluges. Past alerts—like September 17's 45 mm knee-deep flooding at Tonk Road—preview risks: Low-lying zones like Lake Town and Tangra face overflows, with KMC deploying 200 pumps and 500 laborers since dawn. Flash floods along the Adi Ganga canal could inundate 15-20 underpasses, per disaster management reports.

Traffic will grind: Eastern Metropolitan Bypass (EMB) prone to hydroplaning, with 30-minute delays at Ruby crossing; Howrah Bridge bottlenecks worsen with 5 km backups. The Kolkata Metro's Blue Line may halt if lightning hits overhead lines, as in 2023's similar storm. Schools and colleges, including Jadavpur University, announced half-days at 10 AM, while markets like Gariahat shutter by 2 PM. Tourism takes a hit: Victoria Memorial gardens close, and tram rides along AJC Bose halt—September's 2 lakh visitors down 20%.

Agriculture sees mixed blessings: 100 mm replenishes Howrah's paddy fields, but excess risks lodging in 24 Parganas. Power outages loom—lightning downed feeders in 2024, affecting 1 lakh homes. Health alerts rise: Post-rain mosquito surges boost dengue (500 cases YTD, per SSKM Hospital), with civic teams fogging 5,000 km.

Economically, daily losses: ₹100-200 crore from disrupted trade, per FICCI—New Market sales dip 40%, IT parks like Salt Lake lose 2 hours productivity.

Safety Protocols: Thunderstorms and Lightning—What to Do

IMD and KMC urge caution: Stay indoors during peaks (2-6 PM), avoid open fields—lightning claims 2,000 Indian lives yearly, per NDMA. The "30-30 rule"—if thunder follows flash by <30 seconds, seek shelter; avoid corded phones or plumbing. For floods, elevate valuables, use sandbags at doors; dial 108 for emergencies.

KMC's 24/7 war room monitors 500 rain gauges; 100 teams clear 1,000 km of drains. Schools drill "duck and cover"; hospitals stock ventilators for respiratory spikes. Drivers: Wipers on, avoid puddles; pedestrians under awnings. Apps like IMD's Mausam provide radar—essential for 80% rain chance. Tourists: Indoor havens like Birla Mandir or Marble Palace offer refuge.

Historical Echoes: Kolkata's Monsoon Mayhem Through the Years

Kolkata's September storms are legendary—65 mm average over 5 days, but extremes define lore. The 1737 cyclone (1,000 deaths) reshaped the Hooghly; 1970's Bhola (500 mm) flooded the city for weeks. Modern: 2006's 250 mm in 24 hours killed 48, costing ₹500 crore; 2019's 150 mm closed schools for days. 2023's orange alert (80 mm) flooded VIP Road, ₹200 crore losses.

Folklore adds color: Rain gods Indra and Varuna invoked at Kalighat; yellow threads tied at Dakshineswar for mercy. Climate change intensifies: IIT Kharagpur's 2024 study notes 15% wetter Septembers, lightning up 20% since 2010—today's alert fits the pattern.

Broader Ramifications: West Bengal's Monsoon Mosaic

West Bengal's 2025 monsoon—140% excess—has turned deltas to lakes, boosting kharif yields (+15%) but straining Teesta Barrage (95% full). Kolkata's alert ties to statewide troughs, with Howrah facing red risks (150+ mm). Tourism (12% GSDP) weathers it: 2024 rains drew "misty Howrah" crowds, but extremes deter. Policy: 2025 Climate Plan allocates ₹5,000 crore for resilient drains.

Conclusion: Riding Out the Thunder in Kolkata

September 20, 2025's thunderstorm alert envelops Kolkata in a veil of vigilance—a mix of peril and renewal as rain, lightning, and winds lash the City of Joy. From IMD's radar watches to KMC's pumps, the metropolis steels itself, transforming chaos into collective strength. As droplets drum on Howrah's arches, recall: Storms pass, but Kolkata's rhythm endures. Stay safe, stay connected—and let the thunder fade to tomorrow's dawn.