Developing LOW in Bay around 24th September and Heavy Rain Forecast (September 21, 2025)
Disclaimer: This blog post is based on the personal weather assessment (தனிப்பட்ட வானிலை அனுமானம்) provided by MA Rainman for September 21, 2025. Readers are strongly advised to follow official forecasts from the India Meteorological Department and government advice.
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We are tracking significant weather activity across the region, focusing on heavy rainfall opportunities today, primarily influenced by a system over the Bay of Bengal and existing troughs over Central India.
The Developing Threat in the Bay of Bengal
A major system is currently developing off the coast. The upper-air cyclonic circulation (வளிமண்டல மேலெடுக்கு சுழற்சி) that was previously situated near Myanmar has moved back into the Bay of Bengal, specifically lingering near North Andaman and the sea areas adjacent to Myanmar.
Timeline for Intensification:
1. Next Two Days: The system is expected to move in a northwestward direction.
2. September 24th (Third Day): It is predicted to strengthen into a low-pressure area (குறைந்த காற்றெழுத்த தாழ்வு பகுதி) situated between Odisha and Visakhapatnam.
3. After Forming Low in Bay in Subsequent 12 to 18 Hours After Low-Pressure Formation: There is a strong possibility (சாத்திய கூறுகள்) that the system will intensify rapidly into a deep depression (ஆழ்ந்த தாழ்மண்டலம்) or even potentially a small cyclone (சிறு புயலாக).
Heavy Rain Forecast for September 21st
Today's rainfall is also influenced by an upper-air cyclonic circulation over Northwest Uttar Pradesh and a trough (தாழி அமைப்பு) over the Vidarbha district and Central India. Many parts of Central India, Telangana, Andhra Pradesh, Karnataka, Kerala, and Tamil Nadu are expecting rain today.
Kerala and the West Coast
Kerala is anticipating widespread moderate to heavy rain (மிதமானது முதல் கனமலை) that is expected to continue until September 30th.
• Moderate to Heavy Rain: Wayanad, Malappuram, Palakkad, Thrissur, Ernakulam, Idukki, Kottayam, Alappuzha, Pathanamthitta, and Kollam are expected to see widespread moderate or heavy rain.
Karnataka
Most districts have a chance for light rain. Moderate to heavy rain (மிதமானது முதல் கனமழை) is possible in certain areas, including Bengaluru and surrounding regions, Chikkamagaluru, Mysuru, Hassan, Udupi, Dakshina Kannada, Kodagu, Chitradurga, Davangere, Belgaum, Bagalkot, Bijapur, Bidar, Gulbarga, Yadgir, Raichur, and Bellary.
Both states have good chances for rain today, with Telangana expecting widespread moderate to heavy rain, similar to yesterday, including in Hyderabad.
• Andhra Pradesh: Widespread thunderstorms (இடிமழை) are expected in Kurnool, Nandyal, Anantapur, Cuddapah, Satyasaai, Annamaiya, Chittoor, and Tirupati districts. Moderate to heavy rain (மிதமானது முதல் கனமழை) is likely in Nellore, Kavali, Guntur, Krishna, Vijayawada, Godavari districts, Kakinada, Visakhapatnam, and Srikakulam.
◦ Note: Yesterday, the Rayalaseema area did not receive heavy rain, which subsequently reduced the expected rainfall in North Coastal Tamil Nadu, including Chennai
.
• Telangana: Heavy rain is likely in Mahabubabad, Kothagudem, and Khammam. Light to moderate rain (லேசானது முதல் மிதமான மழை) is expected across many other districts, including Mulugu, Jaishankar, Peddapalli, Jagityal, Komarambheem, Adilabad, Nirmal, Nizamabad, Kamareddy, Medak, Sangareddy, Vikarabad, Mahabubnagar, Nalgonda, and Suryapet.
Tamil Nadu (TN)
Widespread moderate to heavy rain (பரவலாக மிதமானது முதல் கனமழை) is expected across several districts today.
• Widespread Moderate to Heavy Rain (TN/Puducherry): This rain is anticipated in Virudhunagar, Madurai, Dindigul, Theni, Karur, Namakkal, Erode (western), Nilgiris, Coimbatore, Perambalur, Kallakurichi, Krishnagiri, Dharmapuri, Tirupattur, Vellore, Tiruvannamalai, Ranipet, Kanchipuram, Chengalpattu, Villupuram, and Puducherry districts.
• Southern Coastal Areas: Light rain (லேசான மழை) is expected in some parts of Nagercoil, Kanyakumari, and Tenkasi. Moderate to heavy rain may occur in certain coastal areas of Thoothukudi, such as Vilathikulam and Sathankulam.
• Chennai and Surrounding Areas: Some parts of Chennai, Tiruvallur, and Chengalpattu adjacent to Chennai may experience light rain (லேசான மழைக்கு இருக்கலாம்). The current "steering" mechanism (ஸ்டீரிங்) is expected to be unfavorable for Chennai. However, if changes occur, the rain currently forecast for the south (Kanchipuram/Chengalpattu) might extend to Chennai.
Staying Updated
Rainfall is expected to increase along the western coastal areas in the coming days as the low-pressure system approaches. While Tamil Nadu will still receive rain, it will be focused on select areas. Stay tuned for daily weather updates to understand how these dynamics evolve.
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