Formation of depression on Thursday and forecast of an eventual away-going cyclone in the North-East Arabian Sea may have just expedited the withdrawal process of the year 2021 South-West monsoon from the western-most outpost of the country bordering Pakistan.

India Meteorological Department (IMD) said that the movement of the depression away from the Indian coast along with a barrage of monsoon winds will allow drier westerly to north-westerly winds to establish over North-West India and trigger the commencement of the withdrawal process.

Anticyclone to build

A seasonal anticyclone marked by higher pressure (the antithesis of monsoon-friendly low-pressure area) will settle over North-West India by October 5, packing the dry westerly-to-north-westerlies, leading to a drastic reduction in moisture and rainfall and triggering the withdrawal from the very next day.

Normally, it takes a month for the withdrawal process to cover the entire geography across Central and adjoining East India before reaching checking into the South Peninsula, leaving the space open for the monsoon in reverse, or North-East monsoon, to set in over Tamil Nadu and neighbouring states.

Space for North-East monsoon

This might change just as in the past years when the withdrawal begins with a delay from extreme North-West India. For instance, the South Peninsula is forecast to witness a fresh spell not too late after Thursday, September 30, the last formal day of the four-month South-West monsoon.

In fact, rainfall activity is forecast to increase over South Peninsular India as early as tomorrow (Friday) with heavy falls over Tamil Nadu, Kerala, Coastal and South Interior Karnataka lasting until Monday. Isolated very heavy falls are also likely over Tamil Nadu from Saturday to Monday.

Bumps along the way

On Thursday, the depression from a reinvigorated cyclone 'Gulab' remnant was located over the North-East Arabian Sea off the Gujarat coast about 60 km West-North-West of Devbhoomi Dwarka; and 280 km East-South-East of Karachi (Pakistan); and 860 km East-South-East of Chabahar Port (Iran).

It may move west-northwestwards, intensify into a deep depression and further into a cyclone by Saturday, moving away from the Indian coast and heading closer to the Pakistan- Makran coasts.

Well-marked 'low' in East

Pausing a monsoon defence in the East is a well-marked low-pressure area over North Jharkhand and adjoining Bihar. The system and its remnant are forecast to move over Bihar and adjoining hills of West Bengal and Sikkim during the next 3-4 days, raining their contents down in the process.

The monsoon withdrawal may also have to contend with a trough in easterlies that runs from the South-East Bay of Bengal to South Andhra Pradesh, which is forecast to persist for the next 2-3 days.

Very heavy rain forecast

Under the influence of these systems, heavy to very heavy rainfall will continue to lash isolated places over Saurashtra and Kutch on Thursday before reducing in intensity significantly.

Isolated heavy falls are forecast over Bihar and the hills of West Bengal and Sikkim till Sunday. Very heavy rainfall is likely also over the plains of West Bengal on Thursday; over Bihar on Saturday; hills of West Bengal and Sikkim both on Saturday and Sunday.

Extremely heavy falls (20 cm or above) are predicted over isolated places over Jharkhand on Thursday and Bihar on Thursday and Friday.