The Met has forecast a wet weekend.

Friday was consistently overcast in Calcutta. The rain was far from heavy in most places, but it was persistent.

"If anything, the rain is likely to be heavier on Saturday and Sunday," said a Met official.

The monsoon trough is now positioned over Calcutta, said a Met bulletin issued on Friday.

"The monsoon trough at mean sea level now passes through Bikaner, Jaipur (both in Rajasthan), Datia, Sidhi (both in Madhya Pradesh), Asansol, Kolkata and thence east southeastwards to northeast Bay of Bengal," the bulletin said.

"An upper air cyclonic circulation lies over northern parts of Gangetic West Bengal and neighbourhood.... An upper air trough runs from north Gujarat to the above cyclonic circulation over northern parts of Gangetic West Bengal and neighbourhood.... In view of the system and strong monsoon flow, light to moderate rainfall at most places
with isolated heavy to very heavy rainfall very likely in some districts of Bengal," it added.

The monsoon trough keeps oscillating.

When it is over the foothills of the Himalayas, north Bengal and the Northeast get rain. When it descends to the northern Bay of Bengal because of a low-pressure system, coastal Bengal gets rain. If the trough descends further, peninsular India gets drenched.

On Saturday, heavy to very heavy rainfall (7-20cm) is very likely in Bankura, East Burdwan, Hooghly and Nadia. Heavy rainfall (7-11cm) is likely in West Burdwan, Purulia, West Midnapore, Murshidabad, Birbhum, North 24-Parganas and South 24-Parganas.

On Sunday, heavy to very heavy rain is expected in Purulia, Bankura, Jhargram and West Midnapore and heavy rainfall is likely in the remaining districts of south Bengal.

On Friday, the clouds and rain kept the Celsius under check.

At 30 degrees, the maximum temperature was almost three notches below normal. Similar conditions are expected over the weekend, said Met officials.