Rain Alert: Heavy Rain Expected as Low-Pressure System Forms Near TN Coast (Diwali 2025 Weather Update)
(Date of Forecast: October 20, 2025)
Good morning everyone, and a very Happy Diwali to all of you from Rainman Studio and Venkatesh MA Rainman!
As we celebrate the festival of lights, our attention turns to a significant weather development. This is my personal weather assessment; please always follow the Indian Meteorological Department (IMD) and government announcements for official advisories.
Understanding the Developing System
Today's forecast centers around a dynamic situation in the Bay of Bengal and the Arabian Sea. Currently, a well-formed low-pressure area is situated in the Arabian Sea. More importantly, the Intertropical Convergence Zone (ITCZ)—the area of tropical convergence—is actively present.
Recently, we observed up to four concurrent upper-air cyclonic circulations, including one near the Comorin Sea/Gulf of Mannar, one near Sri Lanka, another towards the southeast Bay, and the system in the Arabian Sea. This complexity made weather modeling uncertain about which circulation would dominate.
The latest analysis (60-70% certainty) suggests the circulation located in the eastern parts (southeast of Sri Lanka) is set to strengthen. This development is favored by the presence of a Westerly burst. We anticipate this dominant system will strengthen and begin moving in a west-northwestward direction.
Path and Rainfall Impact on Tamil Nadu
Tonight and into tomorrow, the circulation is expected to intensify into a low-pressure area. It is likely to track along the Tamil Nadu coast, with current models suggesting it might cross the coast near Nellore.
When this system approaches the Tamil Nadu coast—starting as early as today and definitely by tomorrow morning—rainfall intensity will increase.
Widespread moderate to heavy rain, potentially coupled with very heavy rain in several areas, is expected across Tamil Nadu for the next two to three days (approximately October 20 to October 23/24).
- Coastal Alert: The Delta districts and North Coastal districts must be vigilant as heavy rain episodes will commence in these areas over the next three days.
- Southern TN: South Tamil Nadu will experience a heavy rain episode today (October 20). After tonight, this heavy rain will gradually lessen, becoming moderate for a couple of days, though rainfall activity is expected to pick up again later.
- System Strength: The system is currently expected to reach a maximum strength of a well-marked low-pressure area or a deep depression, with less probability of strengthening further.
It is worth noting that due to the numerous circulations embedded in the tropical convergence zone, the exact outcomes predicted even 24 hours out can be uncertain. We anticipate more clarity on the dominant system by tonight or tomorrow morning.
Recent Rainfall Highlights (Past 24 Hours)
Heavy rainfall has lashed districts in Western and Southern Tamil Nadu over the last 24 hours.
Notable measurements include:
- Coimbatore: Tholampalayam recorded 194.8 mm.
- Nilgiris: Kengarai saw 134.4 mm, and Nedugulla recorded 97.2 mm.
- Thoothukudi: Pudukottai recorded 96.8 mm, and Thoothukudi city parts saw 66.4 mm.
- Other districts seeing widespread heavy rain include Erode, Tenkasi, and Nellai.
Heavy rain was also reported in Theni and Thiruvarur/Mayiladuthurai districts.
24-Hour State-Wise Forecast (October 20, 2025)
Tamil Nadu (TN): We have many "Yellow points" (indicating potential heavy rain) today. Around 14 to 16 districts face the possibility of heavy to very heavy rainfall.
- Heavy Rain Zones: Nagercoil, Kanyakumari, Tirunelveli, Tenkasi, Thoothukudi, Ramanathapuram, Pudukottai, coastal parts of Thanjavur, Nagapattinam, Karaikal, Tiruvarur, Mayiladuthurai, Villupuram, Coimbatore, and Nilgiris.
- Moderate to Heavy Rain: Widespread moderate to heavy rain is expected across Dindigul, Theni, Madurai, Virudhunagar, Sivaganga, Perambalur, Tiruchirappalli, Kallakurichi, Cuddalore, Pondicherry, Villupuram, Tiruvannamalai, Vellore, Tirupathur, and Ranipet.
- Chennai Region: Chennai, Tiruvallur, Kanchipuram, and Chengalpattu districts saw heavy rain overnight and expect intermittent rain during the day, with chances for more rain tonight/evening.
Kerala: Widespread heavy to very heavy rain is likely in Thiruvananthapuram, Kollam, Pathanamthitta, Alappuzha, Kottayam, Idukki, Ernakulam, Thrissur, Palakkad, Malappuram, and Wayanad.
Andhra Pradesh: Heavy rain is likely for Tirupati, Nellore, and Kavali districts.
Karnataka: Widespread moderate to heavy rain is expected across Bengaluru, Mandya, Hassan, Chikmagalur, Kodagu, Dakshina Kannada, Udupi, Shivamogga, Uttar Kannada, and several northern districts like Belgaum and Rayachur.
Telangana: Widespread moderate to heavy rain, including Hyderabad and surrounding districts like Nagarkurnool, Nizamabad, Warangal, and Mahabubabad.
Stay Safe and Updated
It is significant to note that this marks the occurrence of rain on Diwali after many years. We hope the information provided helps you understand the situation.
Stay safe, have a great day, and we'll see you in the next update.
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