Chennai was among the districts that received surplus rainfall, an excess of 29%, this Southwest monsoon. File
| Photo Credit: The Hindu
The Northeast monsoon over southern peninsular region, including Tamil Nadu, is expected to be above normal this year.
The seasonal rainfall between October and December over the southern peninsular region, including Tamil Nadu and coastal Andhra Pradesh, is most likely to be 112% of the long period average (33.4 cm).
According to the Regional Meteorological Centre (RMC), Chennai, the seasonal outlook of the India Meteorological Department (IMD) has been issued for the entire region. Most parts of Tamil Nadu are likely to experience above normal rainfall. Rainfall may be below normal in some extreme southern districts.
RMC officials said Tamil Nadu usually received an average rainfall of 44 cm during the Northeast monsoon. There are chances for the State to receive up to 50 cm of rainfall. The IMD has observed that there was a 71% probability for the development of La Nina conditions during October-December. (La Nina refers to the cooling of sea surface temperatures in the equatorial pacific, which alters atmospheric circulation and influences rainfall).
B. Amudha, Head, (Additional In-charge), RMC, said that in the past, Tamil Nadu had experienced both poor and surplus rainfall during La Nina years. “There is no direct one-to-one link to La Nina. We must watch the evolution of these conditions to determine its impact,” she added.
Meanwhile, a fresh weather system brewing in the Bay of Bengal is likely to influence scattered rainfall over Tamil Nadu for the next five days. Some northern and delta districts may experience heavy rainspells till October 4. On Thursday, heavy rainfall is likely in Chengalpattu, Villupuram, Kallakurichi, and Tiruvannamalai districts.
Officials of the RMC said a low-pressure area was likely to form on Wednesday, intensify into a depression, and cross the south Odisha-north Andhra Pradesh coasts on October 3. However, parts of Tamil Nadu may also get rainfall as the system moves closer.
Delayed withdrawal
In a virtual press conference on Tuesday, IMD Director-General of Meteorology M. Mohapatra said the developing weather system stalled the Southwest monsoon’s withdrawal. The complete withdrawal may be delayed by a week beyond October 12. This in turn could push back conditions favourable for the onset of the Northeast monsoon.
Mr. Mohapatra added that the October rainfall would be above normal except in some extreme southern districts, which could receive below normal rainfall. This year, the Southwest monsoon officially ended on Tuesday with normal rainfall over Tamil Nadu. Officials of the RMC said the State had received 32.5 cm of rainfall, which is 1% less than the average rainfall of 32.8 cm. However, it is still considered normal monsoon.
Many districts, including Virudhunagar, Tiruppur, Ramanathapuram, and Karur, recorded rain deficits, pulling down the overall State average. Chennai was among the surplus districts with 29% excess rainfall.
Published – September 30, 2025 09:37 pm IST
