A delayed withdrawal of the monsoon is on the cards this year, according to the Met office.
The usual date of the withdrawal of the southwest monsoon from south Bengal is October 12. But this year, weather scientists are yet to spot the telltale signs that mark the withdrawal.
“There is a free flow of southwesterly winds from the Bay of Bengal. The withdrawal of the monsoon is unlikely to start anytime soon,” said G.K. Das, director, India Meteorological Department, Kolkata.
Weather scientists generally treat three to four rain-free days during this time of the year as a prerequisite to announcing the withdrawal of the southwest monsoon. A dip in the moisture content in the air is another marker of the end of the monsoon.
But the most telltale sign is the reversal in the flow of the wind. The end of the monsoon is marked by the arrival of the winds from north India. The winds from the direction of the Bay gradually stop flowing into the city.
But so far, there is no sign of a retreat of the southwesterly winds, said Das. On Saturday, the Met office issued an “enhanced-rainfall” alert for north Bengal and Sikkim, because of “strong moisture incursion from Bay of Bengal”. The rainy spell, in which some districts are likely to see heavy showers, will last till October 12, according to the bulletin.
The monsoon has had a delayed withdrawal for at least the past two years.
Last year, the monsoon left the city on October 23. In 2020, the withdrawal was complete on October 28.
The withdrawal of the monsoon starts from the northwest and gradually covers the east.
Kolkata and the rest of south Bengal have been relatively dry because of the absence of any system over the Bay. A system drives the moisture-laden winds towards south Bengal. The absence of any system gives free access to the winds to move up and reach the hills, said a Met official.
Even without rain, the moisture content in the city has been on the higher side.
On Saturday, the minimum relative humidity — a marker of the moisture content during the driest period of the day — was 55 per cent.
The maximum temperature on Saturday was 35.1ºC, three notches above normal. The conditions are conducive to thunderstorms.
“A cyclonic circulation persists over Uttar Pradesh. As a result, Uttar Pradesh, Bihar and Jharkhand are in the middle of a rainy spell. Some of the clouds formed because of the circulation are likely to reach south Bengal from Monday evening and drag the temperature marginally down,” said Das.