Agri Business

Monsoon onset may lack the usual vigour

Vinson Kurian Thiruvananthapuram | Updated on June 01, 2021

Rains may fail to measure up to give the season its start

India Meteorological Department (IMD) may have pushed back the eagerly awaited onset of the South-West monsoon over the Kerala coast from May 31 to June 3, but global models do not appear to have reached a consensus over ‘classical onset’ conditions developing until at least 4-5 days hence.

Sources tracking the build-up told BusinessLine that the IMD may be able to declare an ‘onset’ on June 3 (Thursday) but the rains may fail to measure up to give the season the usual vigorous start to it. Worse, the rains may not sustain over Kerala though areas to its North may witness reasonably wet days.

Some of this could be even pre-monsoonal in nature, the sources said. There are a series of diagnostic pre-conditions which should evolve fully to set up the usual dynamic onset conditions marked by heavy rainfall over Kerala. But these are conspicuous by their absence at least as of Tuesday.

Weak cross-equatorial flow

Among these pre-conditions are strong cross-equatorial flows from the Southern Hemisphere from deep to the South of Sri Lanka before they turn in as south-westerly winds off the Somalia coast. These winds are hampered by a building cyclone in the South-East Indian Ocean, which is currently redirecting some flows to itself.

This has weakened the cross-equatorial flows. This has, in turn, affected wind speed and direction (orientation) over the South-East Arabian Sea, the gateway for the monsoon into Kerala, which is another pre-condition. Winds are yet to fall in place to being copybook westerly or south-westerly along the Kerala coast.

The other pre-conditions relate to the presence of a classical monsoon vortex that presides over a dramatic onset over Kerala. This vortex usually builds over the South-East Arabian Sea or closer to the Kerala coast and is the fulcrum around which the flows converge before they blast in full strength into the coast.

Offshore trough

Last, but not the least, is the development of a full-blown offshore monsoon trough along the Kerala coast, an elongated area of lower pressure, that might run all the way down from Gujarat to Kerala coast during active monsoon conditions and even act a proxy for the onset vortex that sits farther out in the sea.

There have been instances when the offshore trough has thrown up a vortex-like situation within to preside over a spectacular onset. But none of these are in view as is clear from the weather charts. They won’t evolve at least until the building rogue cyclone in the South-East Indian Ocean weakens, sources said.

Published on June 01, 2021

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