Remnants of powerful tropical storm Wipha, which made landfall in northern Vietnam on Tuesday after sweeping across Southeast Asia, are expected to develop into a cyclonic circulation over the north Bay of Bengal by Wednesday.
The system is tipped to intensify into a low-pressure area by Saturday, according to the Met forecast. Under its influence, south Bengal is likely to receive heavy to very heavy rain between July 24 and 28.
Districts such as South 24-Parganas, Jhargram, East Midnapore, West Midnapore, Bankura, Purulia, Howrah, Hooghly and Calcutta are expected to experience heavy rainfall in this period.
Calcutta is most likely to get heavy rain between July 24 and 26, said a Met official.
Until the low-pressure area takes shape, the city is likely to receive light to moderate rainfall, the official said. But when it does not rain, the conditions are likely to be sweaty and uncomfortable.
A Met bulletin issued on Tuesday stated: “A cyclonic circulation is likely to emerge over north Bay of Bengal during next 24 hours. Under its influence, a low-pressure area is likely to form over the same region in the subsequent 48 hours. An upper air cyclonic circulation... now lies over north coastal Andhra Pradesh and neighborhood.... Due to anticipated low-pressure area over North Bay of Bengal and strong moisture incursion from Bay of Bengal, rainfall activity likely to increase with isolated heavy to very heavy rainfall very likely over districts of south Bengal during July 24-28.”
The monsoon trough is also active and merging into the northeast Bay via Contai in East Midnapore, said the official.
An extended range forecast issued on July 17, valid for a fortnight, had predicted a low-pressure area around July 24-25, with a “low probability” of further intensification into a depression.
The previous low-pressure area over the coastal south Bengal intensified into a depression (on July 14), triggering widespread rain across south Bengal, including Calcutta.
Tropical storm Wipha made landfall in northern Vietnam on Tuesday, bringing strong winds and heavy rain to parts of the country’s north and central regions. Southern parts of the Chinese mainland and Hong Kong were also battered by rain under the influence of the storm.
“After landfall, the storm is moving through land. Facing friction in the form
of poles and trees, it is losing strength. It is expected to reach northern parts of Bay of Bengal via Thailand, Myanmar and Bangladesh. The strong monsoon currents
are expected to revive the system again,” said a weather scientist.