Welcome to our weather analysis for September 29, 2025! As we approach the end of the month, we are statistically at the conclusion of the Southwest Monsoon (SWM) period. Historically, rainfall recorded starting October 1st is typically counted towards the Northeast Monsoon (NEM).
Disclaimer: This is a personal weather analysis; please follow the official forecasts and announcements from the Indian Meteorological Department and government authorities.
Current Weather Systems and the Delayed SWM Withdrawal
The withdrawal of the Southwest Monsoon, which had already advanced into parts of Madhya Pradesh, has currently experienced a stall lasting approximately a week to 10 days.
A significant factor contributing to this delay is the current state of pressure systems over Central and Western India:
1. Western Disturbance: The deep depression that was moving towards Central Indian regions has weakened. As of yesterday evening (September 28), it degraded into a well-marked low-pressure area and has now further weakened into a general low-pressure area concentrated near the coastal regions of Gujarat and Maharashtra. This system is expected to move slowly in the same region for the next 24 hours before exiting into the Arabian Sea the day after tomorrow.
2. Bay of Bengal System: An upper-air cyclonic circulation, or "area of disturbance," is currently hovering over Myanmar. Over the next 24 hours, this disturbance is anticipated to settle as an upper-air cyclonic circulation over the North Andaman parts. This system is projected to arrive as a low-pressure area between Visakhapatnam and Bhubaneswar around October 1st or 2nd.
The persistent movement of these circulations in the region is causing a slowdown (தொய்வு) in the withdrawal of the SWM from Central Indian areas. The complete withdrawal of the Southwest Monsoon from Central India, advancing into Telangana, is now expected sometime after October 7th or 8th, potentially after the 10th.
Transitioning to the Northeast Monsoon (NEM)
Understanding the transition between the two monsoons requires observing the Intra Tropical Convergence Zone (ITCZ). When the ITCZ descends south, the direction of monsoon winds undergoes a critical change, shifting to easterly winds, which marks the commencement of the Northeast Monsoon.
We can anticipate several key markers for the onset of the Northeast Monsoon:
• South China Sea: Northerly winds (Northeast winds) are expected to begin registering over the South China Sea around October 9th or 10th.
• Formation of Circulation: An upper-air cyclonic circulation is expected to form over the southern parts adjoining Andaman around the 13th.
During the SWM period, disturbances generally move westwards from areas like Myanmar, Odisha, Visakhapatnam, and West Bengal towards Central India. However, once the NEM begins, these cyclonic circulations will typically descend southwards and travel in an easterly direction towards Tamil Nadu from the Andaman Sea.
Detailed Rainfall Forecast for September 29, 2025
Rainfall today across various regions is influenced by deep depression activity near Vietnam and strong southerly/southwesterly winds.
Heavy to Very Heavy Rainfall
• Kerala: Widespread moderate to heavy rain is expected to continue today. Districts likely affected include Thiruvananthapuram, Kollam, Pathanamthitta, Idukki, Kottayam, Alappuzha, Ernakulam, Thrissur, Palakkad, Malappuram, Kozhikode, Wayanad, Kannur, and Kasaragod
.
• Western Regions: Heavy to very heavy rainfall is forecast for Goa, Maharashtra (Konkan), and Gujarat.
• Coastal Karnataka: Areas including Kodagu, Dakshina Kannada, Chikmagalur, Hassan, Shimoga, Udupi, and Uttara Kannada, which are part of the Cauvery catchment areas, are likely to see moderate to heavy rainfall.
Moderate to Heavy Rainfall
• Interior Karnataka: Moderate to heavy rain is anticipated in Belgaum, Bijapur, Bagalkot, and the Kalyana Karnataka districts of Bidar, Gulbarga, Yadgir, and Raichur. Other areas, including Bengaluru, may see only light rain.
• Andhra Pradesh: Scattered heavy thermal thundershowers are possible in Tirupati, Nellore, Kavali, Prakasam, Nandyal, Kurnool, Palnadu, Guntur, Bapatla, as well as Northern Coastal Andhra regions like Visakhapatnam, Vizianagaram, Anakapalle, Rajahmundry, and Kakinada. Light rain is expected in Central Andhra and the northern interior parts of Rayalaseema.
• Telangana: Moderate to heavy rain is likely in Nalgonda, Vikarabad, Mahabubnagar, Narayanpet, Wanaparthy, Nagarkurnool, and Jogulamba. This includes the eastern, southeastern, and northeastern parts of Hyderabad. Hyderabad city and surrounding areas may only experience light rain.
Update on Tamil Nadu Weather (வெப்பச்சலன மழை)
Currently, thermal convection rainfall is subdued in Tamil Nadu. This is primarily because, despite the influence of the strong Southwest Monsoon winds (தென்மேற்கு பருவ காற்று வீரியம்), the wind shear necessary to produce rain clouds is currently insufficient.
However, some specific areas are expected to receive rain today:
• Moderate to Heavy Rain: Nilgiris district, Valparai and surrounding Sholayar areas, Kutralam (Tenkasi district), Manjolai (Tirunelveli), Nagercoil, Kanyakumari, and Thiruvallur district may see moderate rain, turning heavy in isolated spots.
• Light Rain/Cloud Cover: Many districts, including Chennai, Kanchipuram, Chengalpattu, Villupuram, Pondicherry, Ranipet, Vellore, Tirupattur, Krishnagiri, Dharmapuri, Salem, Namakkal, Erode, Theni, Tenkasi, Tirunelveli, Thoothukudi, and Ramanathapuram, are likely to see light rain and cloud cover during the evening and night hours.
Looking ahead, widespread thermal convection rain (வெப்பச்சலன மழை) in Tamil Nadu is expected to resume around the evening of October 2nd or starting October 3rd
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