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Humid to dry heat overnight

An airport-bound AC bus caught fire at the Sulekha end of Sukanta Setu in Jadavpur on Thursday morning. Police said people on the road alerted the driver when they saw smoke swirling out of the vehicle’s rear. The fire was put out in 15 minutes. Picture by Sanjoy Chattopadhyaya

Calcutta sizzled in desert-like bone dry conditions on Thursday and the systems that held out hope of rain fizzled out overnight.

The city recorded 37.5 degrees Celsius, a notch above normal, with the maximum temperature maintaining its weeklong course in the upper 30s. The heating was adequate to kick off a storm but the moisture was missing.

At 13 per cent, Thursday’s minimum relative humidity was the lowest in over a year and a four-fold slump in 48 hours from Tuesday’s 46 per cent. On April 2, humidity dipped to 17 per cent and since then it has been oscillating until Thursday’s loo-like low that could cause skin rashes to break out, breathing difficulties and heatstroke in the sun.

The Met office said scorching conditions would prevail till Sunday because systems scattered over Assam, Bengal and Chhattisgarh — which were pulling moisture inland early this week — had run their course while a high-pressure belt or anti-cyclonic circulation over the Bay of Bengal had also shifted away.

The three land systems and the Bay formation, which was pushing moisture to the city, had raised hope on Wednesday.

Weather scientists were banking on the rise in humidity as cure for the heat. But the dwindling minimum relative humidity, which indicates the moisture content in the air during the hottest part of the day, dashed all hopes of rainfall. The weakened systems over Assam, Bengal and Chhattisgarh and the shifting of the Bay high-pressure belt stopped moisture incursion.

“No significant weather system has been observed over eastern India at the moment. Moisture incursion, vital for clouding and rain, is longer happening. We don’t expect rain or squalls over the next couple of days,” said Gokul Chandra Debnath, the director of the India Meteorological Department in Calcutta.

The city went through similar conditions on the first two days of April when a high-pressure belt in central India pushed hot and dry winds to the east. On Thursday, the wind was not oppressive.

An expert said sustained heating and steady supply of moisture over the Chhotanagpur Plateau, the Nor’wester hatchery, could change the tide.