A cyclonic circulation over the Bay of Bengal, which is gradually intensifying, is being monitored round-the-clock by the Met office.
October and November provide conducive conditions for Bay systems to intensify into powerful cyclones that often barrel towards the eastern coast of India.
The Met office said it was still too early to predict if the current system would follow that path.
For south Bengal, dry weather is likely until October 26. After that, light rain and thundershowers are likely for the next couple of days, according to the forecast issued on Thursday.
“The upper-air cyclonic circulation over the north Andaman Sea, off the Andaman Islands, moved west-northwestward and lay over the southeast and adjoining eastcentral Bay of Bengal at 8.30am on Thursday. It is very likely to move west-northwestward and under its influence a low-pressure area is likely to form over the southeast and adjoining eastcentral Bay of Bengal on Friday. Then, it is likely to move west-northwestward and intensify further,” said a Met report.
An official of the Met department in Calcutta said: “Dry weather is most likely to prevail over all the districts of south Bengal till October 26. As of now, light rain is likely on October 27 and 28. By October 26, the system is expected to approach land.”
There is a “medium probability” of the system turning into a depression, the official said.
Sustained intensification turns a depression into a deep depression and then into a cyclone. But many storms weaken before turning into a cyclone.
On Thursday, the Met office could not say whether this system would eventually turn into a cyclone.
A Bay system had intensified into a deep depression before making landfall in Andhra Pradesh on September 23. As the system moved towards Odisha and Chhattisgarh after landfall, it triggered heavy rainfall in Calcutta.
Cyclones feed on heat and moisture. Early summer and post-monsoon months provide conducive sea surface conditions for intensification of tropical storms on the Bay of Bengal.
“There are, however, other factors. A strong vertical wind shear, for example, is detrimental to the intensification of a cyclone,” said the Met official.
In Calcutta, the weather has been sunny and dry for the past few days, including Thursday.
There is just a hint of a nip in the air at night. Fans need not be at full pelt early in the morning.
“If it rains, the maximum temperature will come down. But the minimum temperature will go up,” said the Met official.