The Bay of Bengal is bracing to host the first cyclonic storm of the pre-monsoon season by Saturday morning, almost a week ahead of the predicted onset of monsoon over Kerala, with India Meteorological Department (IMD) indicating rapid intensification of the system to a severe cyclone. 

Onset scenario

The European Centre for Medium-Range Weather Forecasts appears to suggest the monsoon onset scenario predicted by the IMD may largely hold, though the rainfall outlook may wax and wane in view of the impact from the away-going cyclone. The causative low-pressure area had deepened twice over to become a depression on Thursday, and lay centered over the Central Bay at 730 km South-South-West of Khepupara (Bangladesh) and 750 km South of Canning (West Bengal). It may continue to intensify into a cyclone storm over East-Central Bay by Saturday morning and subsequently into a severe cyclonic storm. It is likely to cross Bangladesh and adjoining West Bengal coasts between Sagar Island and Khepupara by midnight of Sunday. 

Surprise to North-East?

Meanwhile, monsoon watchers are tracking the brewing cyclone for signs if the strong Bay arm of the monsoon that it has facilitated, will precipitate the onset over the North-Eastern States. It is the Arabian Sea arm that brings the onset over Kerala, usually ahead of the event that unfolds over the North-East either simultaneously or a day or two behind. The away-going cyclone is diverting a chunk of the monsoon flows brought in by the cross-equatorial winds.

Light to moderate rain is predicted for most places over the coastal districts of West Bengal on Sunday and Monday with heavy to very heavy rain at isolated places. It would be isolated heavy over North Coastal Odisha on Saturday and Sunday and isolated extremely heavy over the coastal districts of West Bengal on Sunday. Light to moderate rain is likely at most places over the eastern districts of the hills of West Bengal on Monday and Tuesday with heavy to very heavy rain at isolated places over

Rainfall scenario

Light to moderate rainfall is forecast at most places with heavy to very heavy rainfall at isolated places is likely over Mizoram, Tripura and South Manipur on Sunday and over Assam & Meghalaya, Arunachal Pradesh, Nagaland, Mizoram, Manipur & Tripura on Monday and Tuesday. Isolated extremely heavy rainfall is likely over Assam & Meghalaya on Monday and Tuesday; Arunachal Pradesh on Tuesday; and over Mizoram and Tripura on Monday. 

As for Kerala & Mahe, Lakshadweep and Coastal Karnataka which usually constitutes the monsoon onset theatre to the farther South-West, the IMD said fairly widespread to widespread light to moderate rain, thunderstorms, lightning and gusty winds are Sunday while it would be isolated to scattered light to moderate over Coastal Andhra Pradesh & Yanam, Rayalaseema, Telangana and Interior Karnataka. Isolated heavy rainfall is likely over Kerala until Monday. 

Wet Andamans & Nicobar

Widespread light to moderate rainfall is likely over the Andaman & Nicobar Islands for next seven days with isolated heavy rain over likely unfolding until Saturday. Isolated light to moderate rain, thunderstorms, lightning and gusty winds are likely over Konkan & Goa and Vidarbha until Saturday thanks to a cyclonic circulation hovering over North-East Madhya Pradesh.