The weak Southwest monsoon circulation, along with El Niño-induced subsidence, is expected to sustain abnormal heatwave conditions over interior Tamil Nadu till July 17 (Friday). The Regional Meteorological Centre (RMC) has forecast an improvement in rainfall over the State from the second half of the week and ease the prevailing heatwave conditions.On Wednesday, many places, particularly interior parts of Tamil Nadu, continued to sizzle as the mercury level climbed above 40 degree Celsius. While the mercury levels hit 41.6 degree Celsius in Vellore, the highest in the State for the day, places like Madurai and Tiruttani too witnessed temperatures exceeding 40 degrees Celsius.Chennai sweltered under searing heat on Wednesday, as Nungambakkam recorded a maximum temperature of 39.4 degrees Celsius, the highest for July in city since 2019. The weather station had previously registered maximum temperature of 40.4 degrees Celsius on July 5, 2019.Meenambakkam too recorded a high day temperature of 40.1 degrees Celsius as strong South-westerlies and dry weather prevailed. The city may have to brace for another hot day as maximum temperature is likely to hover around 38-39 degrees Celsius on Thursday.Officials of the RMC said the weak monsoon circulation over the Southern Peninsular region and El Nino-related atmospheric conditions led to limited cloud formation and unusual heat spell in July. The RMC has issued heatwave warning for isolated places in 19 interior and northern districts, including Vellore, Kancheepuram, Erode, Salem and Madurai, on Thursday as day temperatures may soar two-four degrees Celsius above normal. Seven districts, including Namakkal, Karur and Madurai, are likely to experience heatwave conditions on Friday. Coastal areas of the State are likely to experience hot and humid weather till Friday.V.R. Durai, Head, Regional Weather Forecasting Centre, RMC, said the weak Somali Jet, a low-level wind stream that transports moisture from the Arabian sea is likely to strengthen gradually from Friday and revive monsoon conditions over Southern Peninsular region.A weather system likely over northwest Bay of Bengal would also support monsoon revival. Though the revival may be a weak one, it would still improve cloud cover and rainfall in the State from Friday and help keep temperatures in check.While Madurai has experienced soaring July temperatures, various other places experienced unusual heatwave conditions spread over three to four days, he added. Published - July 16, 2026 12:36 am IST