Chennai: Intense rain spells lashed Chennai’s western suburbs on Thursday morning as the India Meteorological Department (IMD) announced the onset of the northeast monsoon over south peninsular India. The agency has forecast rain of varying intensity across Tamil Nadu over the next three to four days, with heavy to very heavy rain likely along Western Ghats on Friday and heavy rain over Chennai and neighbouring districts on Saturday.An orange alert has been issued for six districts along the Ghats and adjoining areas for heavy to very heavy rain (12- 20cm in 24 hours) on Friday, while a yellow alert covers 20 districts for heavy rain (6-12cm). On Saturday, a yellow alert has been issued for 26 districts, including Chennai, Chengelpet, Tiruvallur and Kancheepuram.V R Durai, director, Area Cyclone Warning Centre, Regional Meteorological Centre, Chennai, said the northeast monsoon was likely to be normal this year. Northern districts may receive below-normal rainfall, southern districts normal to above-normal rainfall, and coastal districts normal rainfall.The rain is being driven by an upper-air cyclonic circulation over south coastal Tamil Nadu and a trough extending from it to the northwest Bay of Bengal off Odisha. The circulation draws moist air upwards, while the trough brings winds together, forcing air to rise, cool and form rain-bearing clouds. The position of these systems will determine where the heaviest spells occur.“Chennai may receive moderate intensity rainfall for the next two days,” Durai said.El Nino may also contribute to above-normal daytime temperatures. IMD has forecast temperatures 2-3°C above normal in isolated pockets over interior Tamil Nadu, while they are likely to be near normal elsewhere.The monsoon is crucial for replenishing water sources after Tamil Nadu recorded a 21% rainfall deficit during the June-Sep southwest monsoon, its third-highest deficit since 2002. The five key reservoirs supplying Chennai held 3,959mcft, or 33.74% of their combined capacity, as of Oct 15. Tamil Nadu receives around 45cm of rain during the Oct-Dec northeast monsoon, nearly 48% of its annual rainfall, while Chennai receives around 87cm, about 60% of its annual total.On Thursday morning, weather bloggers reported intense spells delivering around 40mm in 30 minutes in Ambattur and Ayappakkam. Core city areas remained largely dry, with Nungambakkam recording only traces and Meenambakkam 0.4mm by 5.30pm. Cloud cover kept temperatures down to 32.9°C in Nungambakkam and 30.8°C in Meenambakkam.
