Temperatures during the first half of peak summer, popularly known as the Agni Natchatiram period, are likely to ease across Tamil Nadu as minor weather systems may trigger spells of heavy rainfall over southern and interior districts till May 12.

The peak mercury levels have stayed below 40-degree mark for the past two days in the State, offering respite from the scorching heat. On Wednesday, Erode recorded 39.8 degrees Celsius, marking the hottest temperature in the State for the day.

The Regional Meteorological Centre (RMC) has forecast isolated heavy rainfall in the Western Ghats and neighbouring districts on Thursday, which may spread to southern Tamil Nadu and delta districts until May 11.

On Thursday, 11 districts, including Theni, Madurai, Kanniyakumari, Erode, and Tiruppur, may receive isolated heavy rainfall with gusty winds.

Some parts of Chennai, including Ambattur, Besant Nagar and Korattur, received mild showers in the last two days. This brought down the maximum temperature to 34.6 degrees Celsius and 36.6 degrees Celsius in Nungambakkam and Meenambakkam respectively.

Though light rainfall may continue in the city on Thursday, the humidity levels are expected to remain high.

Several areas in Theni, Tirunelveli, Tiruvarur, Kancheepuram and Ramanathapuram also received moderate rainfall till 6 p.m. on Wednesday.

Officials of the RMC said the prevailing weather systems — an upper air cyclonic circulation over the Gulf of Mannar and a north-south trough running from north interior Karnataka to the Gulf of Mannar — would impact the wet spell over the State.

V.R. Durai, Director, Regional Weather Forecasting Centre, RMC, said that while there were slim chances for the prevailing weather systems to intensify, the weather disturbances may support the wet spell to continue till May 14. Several parts of the State would receive scattered or heavy rainfall.

“We expect daytime temperature to remain in control across the State till May 15. Moisture incursion from the Bay of Bengal and the Arabian Sea is another reason why temperatures are being kept in check,” he said.