The kind of heat India has been feeling this week is more of a burden than before. Humid air is making the feels-like temperature in some cities approach 50C. A short break in the monsoon has let the sun in and held in the dampness, so in Delhi and other urban centres you have the make-up of a sauna even if the thermometer says 32C to 37C.
What changed in the weather this week
By July 9 the southwest monsoon was over all of India, with enough rain to put the season’s deficit in check. But come the 10th or so, the monsoon trough made its way north to the Himalayan foothills. That left drier winds to have their say in central, western and some of peninsular India.
The India Meteorological Department sees subdued rainfall in the offing for central and south peninsular India for the time being. The thing is, the moisture in the ground and the air is still there. Put in some clear skies and hard sunlight and the humidity will do its job of ratcheting up the heat index.
Why 36C can feel like 50C
We cool down by sweating, but for that to work the sweat has to evaporate. If the air is thick with it already, that does not happen. What you are left with is a tiring, sticky feeling well beyond what the numbers would suggest.
That is why there is the heat index, or apparent temperature, to account for the two. Take Bhubaneswar: 36C and 63 per cent humidity works out to a 49.9C index. You see similar in Chennai and Lucknow. In a dry city the same 36C is far more bearable.
Delhi’s sauna effect during a monsoon break
Over the weekend and into Monday, Delhi has been sweltering in the kind of air that is heavy with moisture. While daytime has been in the 32C to 37C range, the apparent temperature has been edging up to 45C. Sunday saw relative humidity at 61 per cent; Monday was not much different at 58 per cent.
This is not an official heatwave, but it is close to it. The break in the monsoon has not cleared the area of dampness. Easterly winds are still moving in from the Bay of Bengal to the Indo-Gangetic plains, and with little in the way of rain to provide some respite, the capital is under a warm, wet blanket.
Where else is it biting, and how hard
It is the coastal and eastern side of the country that is taking it on the chin, with sea breezes adding to the mix. In Mumbai, a 32C day and 70 per cent humidity puts the heat index at 40.4C. Up north in Delhi or Sri Ganganagar, one is looking at 45C to 46C on the index.
There are spots across the nation where the feels-like is in the 40s and 50s, while the actual reading is in the mid-thirties. It is not the dry, searing type of heat of a classic heatwave, but doctors will tell you it is no less of a hazard for the elderly, the young or anyone working outside.
There is no need to overthink it. Drink up and do not push too hard in the middle of the day. It is the best course of action until the monsoon gets back on track and the showers return in force.
What the IMD expects next
For the week of July 9 to 15, the IMD does not have any classic heatwave in the cards. They do note some above-normal maximums in the northwest and northeast, and a below-par rainfall for the month of July in general.
Here is what the official line is for the days ahead:
– Monsoon trough moved north about the 10th
– Rainfall to be light in central and south peninsular India
– Heat index in the 50C range in many a city
– No heatwave to speak of this week, says the IMD
In practical terms, plan for a muggy morning and an afternoon that will seem hotter than it is, with the night offering little in the way of a reprieve. When you are out and about, it is the heat index you should be looking at. How hot it is on your skin is the only figure that counts for the rest of the week.
