Mercury to dip as monsoon prepares to withdraw from North-West

Day temperatures over North-West and Central India are forecast to dip over the next three to four days as the South-West monsoon prepares to exit from parts of the region. 

Specifically, conditions are becoming favourable for withdrawal from parts of North-West India during the next two days, an India Met Department (IMD) outlook said on Tuesday. 

The signature feature of an anticyclonic circulation in the lower and mid levels of the atmosphere, which suppresses cloud-building and rainfall, could likely get established over the region during this period. 

An anticyclone represents clock-wise movement of air, or a 'sinking' motion in the atmosphere, which causes the air to 'sit' over the ground, increasing the ambient pressure. 

This is the exact opposite in a cyclonic circulation (anti-clock-wise motion) making for ascending motion of air, causing it it cool with height gained, later condensing into cloud and dropping down as rain. 

The IMD said that the moisture level in the atmosphere will reduce gradually in the lower levels over the next two days, giving way to dry and cooler air from across the border to fill the lower levels, suppressing rainfall. 

This would set up the right conditions for the monsoon to exit from parts of North-West India initially, before the withdrawal line covers more areas over West, North-West, Central and East India.

By the time the line crosses Central India, conditions would have evolved over the Bay of Bengal, Peninsular India and the Arabian Sea for the retreating monsoon (North-East monsoon).

Super typhoon

A helpful buzz in the adjacent South China Sea/North-West Pacific with a remnant drifting across Indochina and landing into the Bay of Bengal has been seen to trigger the onset of North-East monsoon in the past. 

Already, super typhoon ‘Hagibis’ lurks farther out East in the Pacific with a track towards West-North-West becoming East-North-East and aiming at Japan, the US Joint Typhoon Warning Centre (JTWC) said on Tuesday.

While the initial West-North-West track is considered helpful from the viewpoint of the North-East monsoon, the latter would forfeit the advantage with the away-movement of the super typhoon to East-North-East. 

The Climate Prediction Centre of the US National Weather Service reckons that the next best opportunity may show up during the period from May 17 to 20 when a likely second storm forms over the Pacific waters. 

And this system is expected to travel West-South-West from North-West Pacific into South China Sea, with an onward dispersal of a remnant into the Andaman Sea/South-East Bay of Bengal.

The latest outlook from the US agency says the system might witness development in the North-East Arabian Sea, and not in the Bay of Bengal as expected earlier.

Back home, the IMD has forecast scattered to fairly widespread rains may lash the South Peninsula as well as the East Coast while it would be isolated to scattered rainfall over East and North-East India. 

Isolated heavy falls are likely over Kerala and Coastal Karnataka in what are early signals to the transition from South-West monsoon to North-East monsoon interspersed by chaotic conditions in the atmosphere.

Outlook for Tuesday said heavy rainfall or thunderstorms accompanied with lightning may lash Jharkhand, Odisha, Arunachal Pradesh, Assam, Meghalaya, the North-Eastern States, Madhya Maharashtra, Coastal Andhra Pradesh, Telangana, Rayalaseema, South Interior Karnataka, Tamil Nadu, and Puducherry. 

As for Wednesday, heavy rains may break out over Odisha, Arunachal Pradesh, Assam, Meghalaya, Madhya Maharashtra, Coastal Andhra Pradesh, Telangana, Rayalaseema, North and South Interior Karnataka.

Thunderstorms and lightning are warned over Chhattisgarh, Jharkhand, Bengal, Sikkim, Odisha, Madhya Maharshtra, Marathawada, Konkan, Goa, Coastal Andhra Pradesh, Telangana, Rayalaseema, North and South Interior Karnataka, Tamil Nadu and Puducherry. 

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