Calcutta, June 11: Calcuttans sweated it out as the mercury touched 40 degrees Celsius at 2.30pm today - six notches above normal.

The weatherman, while announcing a heatwave, ruled out rain for at least the next two days.

The RealFeel, as calculated by AccuWeather.com, at noon was 61 degrees. RealFeel indicates the impact of heat and humidity on the skin under the sun.

The Met department expects the maximum temperature to drop by a notch or two tomorrow.

"A trough of low pressure from Rajasthan to Odisha has shifted south into the Bay of Bengal, preventing moisture-rich air from reaching the city," a Met official said.

The lack of moisture in the upper air has made Calcutta and neighbouring areas hotter, he said.

"There's no cloud cover and hot winds are blowing from Madhya Pradesh and Bihar. Pre-monsoon showers are expected after 48 hours when the trough moves back to the Odisha-Bengal coast."

A heatwave is declared when the maximum temperature crosses 40 degrees and is at least 4.5 degrees above normal. The city experienced seven days of heatwave in April and one day in May.

But a heatwave in Calcutta in June is rare, a Met official said.

People found the heat oppressive today because the temperature, along with humidity, started soaring from the morning. At 10am, it was 35 degrees and rose by a degree every hour or so to touch 40 degrees at 2.30pm.

The relative humidity hovered between 50 and 70 per cent around the same time.