The India Meteorological Department (IMD) has issued a heatwave warning for 19 districts of Tamil Nadu on Thursday, 17 July 2025, cautioning that a dangerous combination of soaring temperatures and high humidity could trigger heat-related illnesses across large parts of the state. Authorities have urged residents — particularly children, senior citizens, and those with pre-existing health conditions — to limit outdoor exposure during peak afternoon hours.

Districts Under Heatwave Alert

The IMD has identified the following districts as likely to experience heatwave conditions on Thursday: Madurai, Tirupattur, Vellore, Ranipet, Kallakurichi, Tiruvannamalai, Kancheepuram, Krishnagiri, Dharmapuri, Salem, Namakkal, Karur, Erode, Tiruchy, Ariyalur, Perambalur, Sivaganga, Virudhunagar, and Dindigul. Residents in these areas have been advised to avoid prolonged sun exposure, stay well hydrated, and take precautions especially between noon and 4 pm, when temperatures are expected to peak.

Heat to Persist Into Friday

The intense heat is not expected to relent immediately. The weather department has forecast that heatwave conditions will continue on Friday across Virudhunagar, Sivaganga, Madurai, Dindigul, Karur, Namakkal, and Erode — all interior districts where the absence of sea breeze makes temperatures more punishing. This indicates that the current hot spell could extend across at least two consecutive days for parts of Tamil Nadu's interior.

Partial Relief: Rain Over Western Ghats and Coastal Areas

A slight shift in the speed of prevailing westerly winds is expected to bring some respite. Light rainfall is likely over the Western Ghats districts through Saturday. On Friday, one or two places along the north coastal districts of Tamil Nadu may receive moderate rainfall, while light showers are expected at scattered locations elsewhere in the state.

However, the IMD has cautioned that high temperatures combined with elevated humidity will continue to cause heat-related discomfort along coastal Tamil Nadu through 17 July. The humid conditions are expected to make the weather feel significantly hotter than official temperature readings suggest — a phenomenon commonly referred to as the 'feels like' or apparent temperature effect.

Chennai Weather Outlook

In Chennai, the maximum temperature is expected to reach around 39 degrees Celsius on Thursday. While the city does not fall under the formal heatwave alert, the combination of high heat and elevated humidity is likely to produce uncomfortable conditions throughout the day, particularly during daytime hours. Coastal Chennai typically experiences humidity-amplified heat stress even when temperatures stay below the official heatwave threshold of 40°C for plains.

Public Health Advisory

Health and civic authorities have reiterated precautionary guidelines, urging the public to drink adequate water, wear light-coloured and loose-fitting clothing, use umbrellas or hats when stepping out, and avoid strenuous outdoor activity between 11 am and 4 pm IST. Vulnerable groups — including the elderly, young children, outdoor workers, and individuals with cardiovascular or respiratory conditions — face the highest risk during such heat events. This ranks among one of the most intense heat spells Tamil Nadu has recorded this season.