Kolkata and south Bengal are likely to receive more rain over the coming days as a weather system over the Bay of Bengal is expected to intensify into a depression, according to the Met office. The forecast comes after a sharp thunderstorm brought heavy rain to the city for the second consecutive day on Friday.
An upper-air cyclonic circulation over north Thailand is expected to move towards the north Andaman Sea, where a low-pressure area is likely to form on Saturday, the Met office said. Its extended-range forecast indicates a high probability that the system will intensify into a depression over the east-central Bay of Bengal on September 21 and 22.
The system is then “very likely to move further west-northwestwards towards south Odisha-north Andhra Pradesh coasts during subsequent 3-4 days”, according to the forecast. A depression can strengthen into a deep depression and then a cyclone, although weather systems can also weaken before reaching those stages.
The Met office has forecast “fairly widespread light to moderate rain/thundershower” over south Bengal until September 24. Saturday is also expected to remain rainy, although the intensity of showers in Kolkata is likely to decline compared with Friday.
Kolkata recorded 33mm of rain in Alipore on Friday. A sharp spell of rain in the afternoon reduced visibility and was accompanied by lightning and thunder. The showers were linked to a trough extending from Sikkim to the north Bay of Bengal across Bangladesh at a mean sea level of 1.5km, the Met office said.
Rainfall varied significantly across the Kolkata metropolitan area. Salt Lake received around 65mm on Thursday but recorded only 11mm on Friday. Dum Dum, which also experienced heavy rain on Thursday, received only traces on Friday. The variation indicates that rain intensity has been uneven across the city and its adjoining urban areas.
“Kolkata was rainier than the districts on Friday. The intensity of the showers is likely to go down in Kolkata as well,” a Met office official said.
The Bay of Bengal is generally more conducive to cyclone formation between October and December, though cyclones have also developed in late September in previous years. The current forecast therefore places Kolkata and south Bengal under a period of heightened rainfall watch, even though the eventual strength and track of the system will depend on its development after the low-pressure area forms.
The immediate forecast remains focused on widespread rain and thunderstorms through September 24. The Met office is expected to monitor the system as it moves from the north Andaman Sea towards the east-central Bay and issues further updates on its intensity and track.
