Moist easterly winds ushered in humidity that made the day perceptibly uncomfortable in the Capital despite a 2.4-degree drop in the maximum temperature on Thursday, with weather officials predicting little relief for the time being.
Humidity levels varied between 39% and 62%, leading to a heat index (HI) or “real feel” of 50 degrees Celsius (°C) — which was a 5.4-degree drop compared to Wednesday’s 55.4°C — but still above the 50-degree mark for the second consecutive day. It was 45°C on Tuesday, when the mercury maximum (which measures air temperature) was 42.4°C. Similarly, Thursday’s thermometer high was 41°C, down from Wednesday’s 43.4°C.
The combination of humidity with heat is worse for human health since people cool down by sweating. Heat index is one way to measure this, taking into account both relative humidity and ambient temperature and pertains to conditions recorded in the shade.
Another measure is wet-bulb temperature, which reflects conditions someone will feel outdoors — once this measure passes 32°C, people are at extreme risk of adverse health effects.
Assuming an average humidity level of 50% and a peak temperature of 41°C, the wet bulb temperature on Thursday would have come close to 31.8°C.
According to the India Meteorological Department (IMD), the easterlies, which bring moisture from the Bay of Bengal, are expected to continue till Saturday afternoon, before transitioning to dry westerly winds from Rajasthan. This may lead to heatwave conditions returning to isolated parts of Delhi, the agency said, while issuing an “orange alert” for Saturday, the day of polling, and the two following days.
IMD data from May 13 showed that before Wednesday, the HI was below 50°C on all days. The highest HI during the spell of “dry heat” – when westerlies were predominant – was 46°C on May 16. The maximum that day was 42.5°C.
“Easterly winds began to impact Delhi from Tuesday and gained strength on Wednesday when the HI crossed 55°C. Despite strong wind speed on Thursday, which led to a drop in Delhi’s maximum temperature, the HI remained high as there was a lot of moisture in the air,” Kuldeep Srivastava, scientist at IMD.
Srivastava said Delhi’s maximum is likely to touch 44°C on Saturday and could clock in 45°C on Sunday. The highest maximum at Safdarjung, representative of Delhi’s weather, was 44.4°C on May 19. Across other stations, it touched 47.8°C on the same day. On Thursday, Delhi’s hottest location on Thursday Najafgarh yet again, with a maximum of 42.4°C.