A cyclonic circulation that developed over the South Andaman Sea on Wednesday is likely to intensify into low pressure and thereafter into a depression moving in a northwestward direction, the weather office said.
A close watch is being kept on the movement of the system, it said.
Under the influence of the cyclonic circulation formed over the South Andaman Sea, a low-pressure area is likely to form over the region on May 6, it said.
It is very likely to move northwestwards and intensify gradually into a depression during the subsequent 48 hours, it added.
"We are keeping a close watch on the formation of the system and the subsequent direction it may take," Sanjib Bandopadhyay, deputy director-general of the Regional Met Centre here, said.
The weather office has forecast rain or thundershowers during the next three days in Jhargram, Paschim and Purba Medinipur districts in southern West Bengal and the sub-Himalayan districts of Darjeeling, Kalimpong, Jalpaiguri, Cooch Behar and Alipurduar.