Alipore: The city was transported from monsoon comfort to summer agony on Friday after a typhoon in the Pacific Ocean played catalyst in the maximum temperature shooting up to 40 degrees Celsius, the highest in 765 days.

According to the Met office, the unusual rise in temperature within days of the monsoon setting in might even lead to a heatwave over the weekend. "The south-westerly winds that ferry moisture inland and bring rainfall during the monsoon have been replaced by a north-westerly flow, making conditions sweaty and oppressive," G.K. Das, the director of the India Meteorological Department in Calcutta, said.

The RealFeel temperature during the hottest part of the day was 47 degrees Celsius, two notches above the summer peak. RealFeel reflects the impact of heat and humidity together on your skin.

Since the forecast for the next two days does not include any rain, the torment could get worse. A heatwave will be declared if the temperature stays at or exceeds 40 degrees.

June 11, 2016, was the last time that Calcutta experienced 40-degree heat, This year, the monsoon arrived on that date and there was heavy rainfall across the city and its neighbourhood the next day.

According to meteorologists, it is very unusual for a heatwave-like situation to develop after the monsoon hits. This anomaly has been caused by the south-westerly wind flow from the Bay of Bengal drying up suddenly. The heat surge is because of the north-westerly wind blowing in from the hot plains of north and central India.

Two correlated factors have influenced the change in wind direction - a typhoon in the Pacific Ocean and the absence of a strong weather system like a low-pressure area on the Bay of Bengal to push moisture inland. "When there is a strong weather system like a typhoon in the Pacific Ocean, you generally don't have another strong system over the Bay of Bengal," Das said.

Between Monday and Friday, the temperaturehas increased from 34.1 to 40 degrees. The highest spurt of three degrees was in the past 24 hours.

For immediate relief, the city's best bet is a summer-like thundershower or two. "Normal monsoon rainfall seems unlikely, so the only source of hope is the possibility of thunderstorms. Heat and humidity are required for thunderclouds to form and both these components are present in the air at the moment," Das said.