The maximum temperature on Wednesday touched 31.1 degrees Celsius, four notches above normal and the highest in 80 days.
The weatherman expects the maximum temperature to go up further on Thursday.
Met records show that the maximum temperature had last been higher on November 19, when the mercury had touched 32 degrees Celsius.
Since then, the maximum had hovered around the 30-degree mark on only two days ' November 21 and 24.
With the sky clear at night, allowing the radiation to escape, Wednesday's minimum temperature, recorded early in the morning, dropped to 15.7 degrees Celsius, the normal level.
"It was hot and stifling in the evening. I had to switch on the air-conditioner in my car around 5.30pm," said public relations professional Chilka Roy.
That is not surprising because the temperature in the city then was 25.4 degrees Celsius and the relative humidity 61 per cent.
"A western disturbance is responsible for the warm weather in Calcutta. Satellite pictures suggest that the weather is unlikely to change much immediately. On the contrary, the day temperature might increase marginally," said a senior official at the Alipore Met office.
He said the western disturbance was drawing moisture from the sea. The water vapour in the air was making things muggy in Calcutta and blocking the flow of the northwesterly wind that brings cold to Calcutta.