Chennai: After several days of short, isolated spells, rain activity may intensify over the city and neighbouring districts in the coming days. The IMD has forecast moderate rain at one or two places in Chennai, Tiruvallur, Chengelpet, Kancheepuram and other north Tamil Nadu and interior districts on Thursday and Friday. Heavy rain has also been forecast over Tiruvallur on Saturday.V R Durai, director, Area Cyclone Warning Centre, IMD, said an upper-air circulation over south coastal Andhra Pradesh and adjoining Rayalaseema, along with a trough extending from north interior Karnataka to the Gulf of Mannar, may bring rain to the city, neighbouring districts and other parts of Tamil Nadu.An upper-air circulation is an area where winds rotate around a region of relatively low pressure several kilometres above the ground. It can draw moisture into the atmosphere and encourage air to rise. As the moist air rises, it cools and condenses into clouds, which may produce rain when conditions are favourable. A trough is an elongated zone of relatively low pressure that can also bring winds together, supporting rising air and cloud formation.“It may not be widespread rain in the city, but moderate spells are possible in some areas till Sept 20,” Durai said.On Sept 17 and 18, thunderstorms and lightning, accompanied by gusty winds reaching 40-50kmph, may occur in some areas. On Thursday, the city and suburbs may receive light to moderate rain during the evening and night, with partly cloudy skies. Daytime temperatures may be 35-36°C, while nighttime temperatures may remain around 27-28°C.Since June 1, Chennai has recorded 361.4mm of rain, around 2% below normal. Nungambakkam recorded 392.7mm, about 10.7mm above normal, while Meenambakkam received 422.4mm, around 6.1mm below normal. Tiruvallur has recorded 86.3mm, 22% below normal; Kancheepuram, 264.6mm, 33% below normal; and Chengalpet, 154.5mm, 54% below normal.
