Thursday’s rain brought much-needed relief to a city that had remained largely dry since the monsoon arrived on June 11.

Apart from a mere 1.4mm of rainfall on the day the monsoon reached Calcutta, the Met office had recorded no rain in Alipore for six consecutive days, from June 12 to
June 17. The showers on Thursday helped cool the city after days of warm and humid weather.

Met officials said monsoon currents remain weak over south Bengal but strong across the northern districts. While several areas in Alipurduar and Jalpaiguri received heavy rain earlier in the week, only light showers were reported from parts of south Bengal, including East and West Burdwan.

“The seasonal trough runs from Punjab to Bihar in the lower tropospheric levels. It is close to the foothills of the Himalayas. The monsoon currents are strong in north Bengal. In south Bengal, the currents are weak at the moment,” said an official at the Regional Meteorological Centre in Alipore.

When the southwest monsoon covers the entire India, the seasonal trough is called the monsoon trough. The monsoon trough keeps oscillating.

When the monsoon trough lies along the Himalayan foothills, north Bengal and the Northeast receive rain. If a low-pressure system pulls it south towards the northern Bay of Bengal, coastal Bengal gets rain. A further southward shift brings widespread rainfall to peninsular India.

In Calcutta, the monsoon currents may get some steam after June 20, said the Met official. After June 20, the chances of light to moderate rain will go up.

“But even after June 20, heavy rain is unlikely in Calcutta. The trough will not be stationed here. It will keep oscillating,” the official said.

On paper, light to moderate rainfall is not ruled out in East Burdwan, West Burdwan, Birbhum, Murshidabad, Nadia, Purulia and Bankura on Friday.

In the absence of rain, the conditions have been uncomfortable. The heat, coupled with high humidity, made conditions extremely uncomfortable.

“There is no long relief from the oppressive weather for now. The readings are not likely to change significantly for now,” said the official.