Fresh ‘low’ in Bay will oversee monsoon revival

A fresh low-pressure area has formed over North-East Bay of Bengal on Thursday morning even as a rain-driving counterpart ‘low’ from erstwhile very severe cyclone ‘Vayu’ faded out over North-West India.

This sets up the environment for a fresh west spell from the ongoing monsoon after its orderly flows were disrupted during the first week of the onset and guided North along the coast by ‘Vayu.’

Two vital cogs

Formation of the new ‘low’ has also ensured that two vital cogs are in place for the larger monsoon wheel — an offshore trough along the West Coast and a shear zone of wind turbulence in the higher atmosphere.

The offshore trough, which lay extended on Thursday from South Maharashtra to Kerala coast, acts as the receptacle for moisture mopped from the seas and is a proxy for healthy monsoon conditions.

During ‘active’ to ‘strong’ monsoon conditions, the offshore trough lies extended full length along the West Cast from Gujarat in the North to Kerala in the South.

Similarly, the shear zone of monsoon turbulence in the upper atmosphere (over peninsular India) is where the most active monsoon conditions prevail with opposing winds running into each other.

It also sets up the platform for rain-bearing systems (low-pressure areas depressions et al) to play around in. The shear zone strengthens in tandem with the strength of the monsoon.

This apart, a land-based trough lies from Punjab to the centre of the ‘low’ in the Bay across Haryana, North Madhya Pradesh, North Chhattisgarh, Jharkhand and north Odisha.

Monsoon trough

This would be a precursor to the all-important North-West to South-East-oriented trough that sets up the highway (monsoon trough) for monsoon clouds to drift in from the Bay into Central and North-West India. In this context, the arrival of a fresh western disturbance from across Afghanistan-Pakistan into North-West India is significant, viewed from the view of rain-generating potential.

An interaction with the opposing western disturbance and the monsoon clouds from the Bay throws up the prospect of heavy to very rainfall over the farming heartland of the country.

The India Met Department (IMD) said rains will break out over Karnataka, Maharashtra, parts of Andhra Pradesh, Telangana, remaining parts of Tamil Nadu, North-East India, and some parts of Bengal, Sikkim, Bihar, Jharkhand and Odisha during the next three days.