The wettest month in Kolkata based on a 30-year average has so far registered a nearly 60 per cent rain deficit.
Between July 1 and 26, the city usually gets around 317mm of rain, based on Met figures over the past three decades.
In the same period this year, the Met office has recorded just 129mm of rain in Alipore, which serves as the official record for Kolkata. The gap translates to a deficit of 59 per cent.
The average July rain in Kolkata is around 370mm.
The past few days have been rainy and generally overcast. But the showers have been far from enough to narrow the yawning deficit.
Between Monday and Thursday, the Met office recorded around 42mm of rain in Alipore.
A Met official attributed the deficit to the absence of heavy rain.
"The city is yet to get a single day of heavy rain in July. Technically, there has not been a single day of heavy rain in Kolkata this monsoon. The number of rain days (when the Met office records some rain in Alipore) has not been unusually low. But the lack of heavy rain has led to the deficit," said the official.
Between June 27 midnight and June 28 morning, several parts of the city were lashed by more than 60mm of rain, which qualifies as heavy in Met parlance. But the Alipore Met office, which serves as the official recordkeeper for Kolkata, had received less than 60mm in the same phase.
The Met office spies a wet weekend in the city. But the monsoon deficit will at best get narrowed somewhat, said G K Das, director, India Meteorological Department, Kolkata.
"A low-pressure area is over south Odisha and adjoining north coastal Andhra Pradesh. The monsoon trough runs into the west-central Bay of Bengal, near the system. As the low-pressure area moves further inland into Telangana and Andhra Pradesh, the monsoon trough is likely to rise and come closer to Kolkata. Under its influence, there is a possibility of an increase in the volume of rain in Kolkata during the weekend," said Das.
"But since heavy rain is unlikely, the margin will get reduced at the most," he said.
Telangana and adjoining areas are already in the middle of heavy rain under the influence of the system.
Monsoon rain in lower Gangetic Bengal is dependent on low-pressure systems over the Bay. For a long time since June, there had been a lull in low-pressure areas over the Bay of Bengal. In less than two weeks, two more low-pressure areas took shape over the Bay. But both of them formed far from Kolkata.
"A system over the northeast Bay or north Bay, near the Bangladesh coast, is most suited to bring heavy rain to Kolkata. So far this season, there has been none," said a Met official.
The city's cumulative rain deficit for this season stands at 49 per cent. Between June 1 and July 26, the city's usual quota is 600mm. In the same period this year, Kolkata got only 303.5mm.