The Hindu Business Line : ‘Shear zone’ looms as clouds gather

India Meteorological Department (IMD) has declared that the ‘east-west shear zone of turbulence’ will get established over the peninsula as early as Friday in the firmest yet indication that the Northeast monsoon is just around the corner.

In fact, southern China has already started receiving the Northeast monsoon rains, and the prevailing easterly wind regime is slowly giving into being northeasterly, as per updates by leading weather models.

Shear zone is where the winds change speed and/or direction rapidly over a given distance. Wind shear along the zone can generate ‘eddy’ currents that are sometimes visible as billow clouds. These small eddies and whirling masses of air move in various directions, generating tremendous turbulence.

IDEAL BACKDROP

This provides the required backdrop for Northeast monsoon to prosper; more so when a circulation gets embedded into the shear zone. This drives up the turbulence manifold, often generating storms in the nearby seas and dumping rains along the coast and progressively into interior peninsula.

The European Centre for Medium-Range Weather Forecasts (ECMWF) predicts the formation of a system in the southwest Bay around the weekend. But it may fail to intensify, and loiter around along the southeastern coast for sometime.

A counterpart circulation is shown evolving over the Arabian Sea, but this would most likely be the manifestation of the larger shear zone that extends to the west across the peninsula. Two systems embedded into the shear zone on either side of the peninsula represents the most potent phase of the Northeast monsoon.

In its update on Thursday, the IMD said the scattered rainfall currently over the Northeastern States would subside over the next three days.

This would be matched only by the gradual scale-up of rainfall over the southern peninsula.

The seasonal anticyclone will make further inroads into the South, expediting the withdrawal of the Southwest monsoon from most parts of Maharashtra and many parts of east and central India during the next five days.