Chennai and several other districts of Tamil Nadu are likely to receive heavy rainfall on Sunday, October 18, with the Regional Meteorological Centre (RMC) forecasting further intense spells amid the active northeast monsoon. The forecast follows heavy rain on Saturday, October 17, when parts of Chennai recorded more than 300 mm. The downpour inundated roads, disrupted traffic and increased the combined storage of the city’s five principal drinking water reservoirs by 237 million cubic feet (mcft) over two days.
On Sunday, Chief Minister Vijay inspected the Greater Chennai Corporation headquarters at Ripon Building to review preparations for the northeast monsoon and stormwater drainage measures.
The RMC has forecast heavy rainfall at isolated places in Chennai, Tiruvallur, Kancheepuram, Chengalpattu, Villupuram, Cuddalore, Salem, Krishnagiri, the Nilgiris and several other districts. The department attributed the rainfall to a cyclonic circulation over northern Tamil Nadu and adjoining southern coastal Andhra Pradesh.
The RMC said significant convective cloud development over north coastal Tamil Nadu and adjoining sea areas, associated with the circulation, could bring heavy to very heavy rainfall to Chennai and its neighbourhood on October 18.
The RMC has issued a yellow alert for 17 districts, particularly in northern and interior Tamil Nadu, with heavy rainfall expected to continue in several parts of the state until October 23. Isolated very heavy rainfall of up to 20.4 cm is possible in districts along the Western Ghats, including the Nilgiris and Theni, on October 20. An orange alert has also been issued for heavy to very heavy rainfall at isolated places in the Nilgiris, Coimbatore, Tiruppur, Dindigul, Theni, Tenkasi, Virudhunagar, Tirunelveli and Kanniyakumari districts that day.
The RMC expects rainfall intensity across Tamil Nadu to ease after October 25. Another weather system is likely to form over the Bay of Bengal around the last week of October. Meanwhile, a low-pressure area is likely to form over the southwest Arabian Sea around Monday, though it is not expected to bring significant rainfall to Tamil Nadu.
Chennai experienced an intense spell of northeast monsoon rain on Saturday, with two rainfall stations recording more than 300 mm. Hourly rainfall data from the Greater Chennai Corporation’s Integrated Command and Control Centre (ICCC) and the Tamil Nadu Disaster Risk Reduction Agency showed that Zonal Office 1 in Kathivakkam recorded 310.2 mm of cumulative rainfall by midnight, while Parrys recorded 300.9 mm.
Rainfall intensified after 9 pm on Saturday, with 26 weather stations, including 20 in Chennai, recording more than 100 mm. Sathangadu recorded 234.4 mm, followed by Tiruvottiyur with 198.6 mm, Ennore with 192.4 mm and Kargil Nagar with 180 mm.
The Chennai Corporation recorded average rainfall of more than 105 mm in the 24 hours up to 6 am on Sunday. Six localities—Tiruvottiyur, Kathivakkam, Ennore, Parrys, Chennai Central and Meenambakkam—received very heavy rainfall.
Between 6 pm on Saturday and 6 am on Sunday, Meenambakkam recorded 28.5 cm of rain, Chennai Central 27.4 cm, Ennore 21.5 cm and Tiruvottiyur 22.4 cm.
The India Meteorological Department (IMD) said the rainfall appeared to have resulted from widespread convective activity associated with a cyclonic circulation, rather than an isolated cloudburst.
“In India, a cloudburst is conventionally described as an event in which 100 mm or more of rainfall occurs within one hour over a small area, typically around 20–30 square kilometres,” the department said.
“Based on the prevailing meteorological conditions and the observed rainfall pattern associated with the cyclonic circulation, the rainfall over Chennai and its neighbourhood appears to have resulted from organised, widespread convective activity associated with the cyclonic circulation, rather than an isolated, highly localised cloudburst event,” it added.
Heavy rain flooded bus routes, interior roads and several major arterial stretches across Chennai. Traffic moved slowly on Anna Salai, while G N Road, which connects T Nagar to Anna Salai, was among the roads affected by waterlogging. Several vehicles were stranded as water levels rose.
Waterlogging was also reported along Velachery Main Road, near the Guru Nanak College signal, and in parts of Besant Nagar, where ankle-deep water was reported. Water levels rose in Madipakkam’s Kuberan Nagar Extension, Govindasamy Nagar, LIC Nagar and Sadasivam Nagar.
In North Chennai, Perambur and Tiruvottiyur were among the affected localities. Other stretches reported to have experienced waterlogging included Perambur High Road near Julian Nursing Home in Jamalia, areas near Perambur railway station, Perumal Koil Street in Kadirvedu, Bunder Garden in Perambur, Arthoon Road and Shaik Maistry Street in Royapuram, and parts of Navalur.
Rainfall over the past two days increased the combined storage of Chennai’s five principal drinking water reservoirs—Poondi, Red Hills, Cholavaram, Chembarambakkam and Kannankottai-Thervoykandigai—from 3,949 mcft on October 16 to 4,186 mcft on October 18, according to Chennai Metropolitan Water Supply and Sewerage Board data cited by The New Indian Express.
The reservoirs’ combined storage rose by 197 mcft on Sunday alone, from 3,989 mcft on October 17 to 4,186 mcft on October 18.
Red Hills recorded the largest daily increase, with storage rising by 111 mcft, from 1,926 mcft to 2,037 mcft. It received an inflow of 1,485 cusecs, while its outflow was 196 cusecs.
Poondi and Chembarambakkam each recorded an increase of 39 mcft. Poondi’s storage rose from 358 mcft to 397 mcft, with an inflow of 980 cusecs and an outflow of 530 cusecs. Chembarambakkam’s storage increased from 1,351 mcft to 1,390 mcft, with an inflow of 655 cusecs and an outflow of 203 cusecs.
Cholavaram’s storage increased by 8 mcft, from 122 mcft to 130 mcft. It received an inflow of 102 cusecs and recorded an outflow of 8 cusecs. Kannankottai-Thervoykandigai remained unchanged at 232 mcft, with an inflow of 20 cusecs and an outflow of 18 cusecs.
The reservoirs’ combined storage stood at around 35.6% of their total capacity of 11,757 mcft on October 18. Red Hills was at 61.73% of capacity, followed by Kannankottai-Thervoykandigai at 46.4%, Chembarambakkam at 38.13%, Poondi at 12.29% and Cholavaram at 12.03%.