A system that would have moved deep into Madhya Pradesh even a fortnight ago is lingering on the Bengal-Jharkhand border and triggering rain in Calcutta.
A change in the direction of winds has blocked the movement of the system into central India, said a Met official.
The weather in Calcutta is likely to be cloudy and rainy on Wednesday and Thursday as well, according to the forecast. The rain is expected to subside from Friday.
“The low-pressure area on the Bay entered land (around October 1) while moving along the Odisha-Bengal coastline. In July, August and even till the third week of September, such a system usually moves up to Madhya Pradesh via Odisha, Jharkhand and Chhattisgarh, riding the easterly winds from the Bay. Once there, it is too far from Bengal to have any impact here,” said G.K. Das, director, India Meteorological Department, Calcutta.
“But now, the direction of the winds has changed. Westerly and northwesterly winds are dominant in the upper levels of the atmosphere in much of the northwestern and central India. The winds from the opposite direction are pushing the system back to Jharkhand,” said Das.
Moisture-laden easterly winds flow from the east to the west, from the Bay towards central India. Northwesterly and westerly winds flow from west to east.
A Met bulletin on Tuesday said the monsoon had retreated from Rajasthan and parts of Gujarat, Madhya Pradesh, Uttar Pradesh and Uttarakhand.
But in Calcutta, the sky has been overcast since Tuesday morning. And the day was marked by intermittent spells of rain.
Between 6am and 2pm, Jodhpur Park got around 45mm and Behala around 30mm of rain, according to figures from the pumping stations of the Calcutta Municipal Corporation. In the north, Maniktala got around 26mm and Belgachhia 20mm.
The Met office recorded around 20mm of rain in Alipore between 8.30pm on Monday and 8.30pm on Tuesday.
“Yesterday’s low-pressure area now lies over southeast Jharkhand and neighbourhood. It is very likely to move nearly eastwards during next 2-3 days across Bengal,” said the Met bulletin on Tuesday.
Heavy rain is likely in Birbhum, Murshidabad, Nadia, North 24-Parganas, South 24-Parganas, East Burdwan and West Burdwan districts on Wednesday.
West Burdwan, Nadia, Birbhum, South 24-Parganas and Murshidabad are likely to get heavy rain on Thursday as well, the bulletin said.
The north Bengal districts of Kalimpong, Jalpaiguri, Alipurduar, Darjeeling, Cooch Behar, Malda, North Dinajpur and South Dinajpur are likely to get heavy rain on Wednesday and Thursday.
After a lacklustre performance in July and August, the two rainiest months, the monsoon picked up steam in Calcutta in September.
In the city, the combined rainfall in June, July and August was around 660mm. In comparison, the rain in September alone was over 450mm.
Thanks to the late surge, the monsoon deficit in Calcutta now stands at 17 per cent. The deficit was over 45 per cent at the end of August.
The monsoon usually withdraws from Calcutta between October 10 and 12.
Das, of the Met office in Alipore, said it is still not clear when the monsoon would retreat from the state this year.
“There is no immediate chance of another system on the Bay. But unless the present low-pressure system dissipates, it will be too early to comment on the date of the withdrawal of the monsoon,” he said.