The mercury dipped to a three-week low in Calcutta on Sunday but the drop was offset by rising humidity.

The Met office recorded a maximum temperature of 36.4 degrees in Alipore. It was a notch above normal. It was also the lowest day temperature after April 12. On that day, the maximum temperature was 35.2 degrees Celsius.

The minimum relative humidity — a marker of the moisture quotient in the air during the driest part of the day — of 54 per cent teamed up with the heat to torment Calcuttans who stepped out on Sunday.

Around 2.30pm, the temperature was 36 degrees but the RealFeel shot up to 45. The humidity was 61 per cent.

“For most of Sunday, the relative humidity was over 60 per cent. That is why the day felt so sweaty and exhausting,” said a Met official.

A combined assault of heat and humidity is nothing new to Calcuttans. But for most of April and the first couple of days in May, the heat was devoid of moisture.

The rise in the discomfort index strengthened the yearning for a thundershower. But on Sunday, it was not to be. “It is not ruled out on Monday. But Tuesday and Wednesday are more likely to see thunderstorms in Calcutta,” said a Met official.

“A cyclonic circulation lies over northeast Assam in lower tropospheric levels. Another cyclonic circulation lies over northeast Bihar and a trough runs from this cyclonic circulation to north Odisha in lower tropospheric levels,” said a press release from the Met headquarters in Delhi.

An official at the Regional Meteorological Centre in Alipore said: “The weather systems are likely to change positions and become conducive to thunderstorms in
Bengal.”

The forecast, according to a Met bulletin issued on Sunday afternoon:

Monday

• Thunder squall with wind speed reaching 50-60km an hour likely in Birbhum, East Burdwan, Hooghly, Nadia, Murshidabad and North and South 24-Parganas
• Heavy rain likely in Birbhum, Nadia and Murshidabad
• Thunderstorm with lightning and gusty wind (30-40km an hour) likely in some places in the remaining districts of south Bengal.

Tuesday

• Thunder squall with wind speed reaching 50-60km an hour likely in Calcutta, North and South 24-Parganas, Howrah, Hooghly, East and West Midnapore, Bankura and Jhargram
• Heavy rain likely in East Midnapore, North and South 24-Parganas
• Thunderstorms with lightning and gusty wind (40-50km an hour) are likely in some areas in the remaining districts of south Bengal.