At 40°C, Capital feels like 52°C as high humidity spikes heat index

Delhi’s wet-bulb temperature was 32.11 degrees on Sunday, also the highest so far for the capital this year. Both these measures are likely to remain high over the next couple of days, weather officials said.

Although Monday was not the hottest day this year in Delhi by far, it certainly felt that way as the moist east wind raised humidity levels in the capital, which combined with temperatures over 40 degrees Celsius to make most locations unbearably sultry. The mercury touched 40.2 degrees at 2.30pm in Safdarjung, the capital’s base weather station, at a time when humidity was at 45%, taking Delhi’s heat index, or real feel, to 52 degrees, the highest so far this year.

People in Delhi can expect some relief only from June 30.(ANI Photo)

Delhi’s wet-bulb temperature was 32.11 degrees on Sunday, also the highest so far for the capital this year. Both these measures are likely to remain high over the next couple of days, weather officials said.

The heat index (HI) is a function of maximum temperature and humidity, but calculated in the shade. The wet-bulb temperature takes into account maximum temperature, humidity, wind speed, and solar radiation, and is calculated in the sun (under direct sunlight).

Wet-bulb temperatures of over 32 degrees makes it difficult for even fit and acclimatised people to work outdoors. At a wet-bulb temperature of 35 degrees, humans can no longer regulate body temperatures, leading to heatstrokes and potential collapse.

Since the southwest monsoon is nearing, the impact of easterly winds was visible over Delhi, with humidity levels doubling compared to the first half of June, said RK Jenamani, a scientist at India Meteorological Department.

“We saw high temperatures in the first half of June, but humidity at the time was around 20% or 25% and it was not uncomfortable. Since June 25, we have seen a maximum over 40 degrees and the humidity has been around 40-50%.” he said. “This is a dangerous combination and is leading to considerable discomfort.”

People in Delhi can expect some relief only from June 30.

“Over the next two days, we expect the maximum to remain over 40 degrees and humidity will remain in a similar category,” Jenamani said. “Therefore, avoiding exposure outside and hydrating oneself is important. On June 30, owing to rains and gusty winds, the maximum temperature will drop considerably and Delhi will see relief.”

Delhi’s maximum temperature at Safdarjung is likely to rise to 41 degrees by Tuesday and touch 42 degrees on Wednesday, the weather office predicted.

Safdarjung recorded a maximum of 40.9 degrees on Monday, three degrees above normal, while the minimum was 29.8 degrees, two notches above normal. However, it was the high humidity that played a key role in the discomfort, with the highest humidity recorded at 72% and the lowest at 46%.

Readings from Safdarjung at 2.30 pm on Sunday showed that while ambient temperature was 39.6 degrees, the humidity levels of 41% meant the heat index, or the real feel outdoors was 48 degrees, according to weather forecasting channel Live Weather of India.

Delhi’s hottest day of the year so far was on May 15, when temperatures touched 45.6 degrees at Safdarjung. However, it was largely dry heat at that time, with humidity at around 10-15%, translating to a heat index of 45 degrees.

Easterly winds carrying moisture are to blame for the prevailing discomfort over northwest India, including Delhi, said Mahesh Palawat, vice president of meteorology and climate change at Skymet Weather Services, a private forecaster. Relief will depend on rain, he said.

“These are humid winds and there is high temperature too, the combination of which is responsible for this discomfort,” Palawat said. “Relief is in sight as rains are possible from June 29, and the monsoon may reach Uttarakhand, Uttar Pradesh, Rajasthan and Delhi by around June 30 or July 1.”

Meanwhile, India Meteorological Department (IMD)’s seven-day forecast shows Delhi is likely to record a high of 41 degrees Celsius on Tuesday, with south-easterly winds blowing towards the Capital. On Wednesday, Delhi is likely to see a high of around 42 degrees during the day, with the wind direction expected to be easterly. While it has only forecast ‘thundery development’ for Tuesday, Delhi is likely to see light rain towards Wednesday evening. On both days, the humidity levels are likely to remain high, keeping the discomfort level high too.

The IMD has been working on developing a model that can incorporate Heat Index alongside the day’s maximum temperature, however, this is likely to take some time. A met official, working on this, says warnings being issued by the IMD are already incorporating the possible impact of high humidity. “Based on the humidity levels, a yellow alert can be upgraded to an orange alert. Soon, we will see the Heat Index also as part of the daily temperature model,” the official said.

The onset of the monsoon is expected to bring the capital relief in terms of the humidity as well. The IMD says it will be declaring a possible onset date for Delhi on Tuesday.