The Hindu Business Line : Weak winds may hit N-E monsoon build-up

The shear zone of monsoon turbulence may have organised itself to some extent, but the northeasterly wind component has failed to strike the desired depth, said Dr Akhilesh Gupta, Advisor to the Department of Science and Technology.

ORIGIN OF WINDS

To the west, the southwesterly wind component has to blow in from a position out in the open seas, away from the south of the peninsular tip. The flow from an offshore trough directed into the land, which was the order till only the previous day, is a feature identified with the southwest monsoon.

This has to die out completely if northeasterlies are to blow in freely. This is one factor that could impair the northeast monsoon onset features. The criss-crossing flows from southwesterlies and northeasterlies throw up the shear zone of turbulence, where rain-bearing systems prosper.

Anomalous positioning of the seasonal anti-cyclone also is adding to the complexity of the situation. The anti-cyclone (high-pressure zone heralding clear weather) advances in from Northwest India on the heels of a withdrawing southwest monsoon. It extends its reach gradually southward.

But it has not moved sufficiently south, preventing the associated core of southeasterly flows from favourably influencing the northeasterly monsoon winds.

RIGHT COMBINATION

According to Dr Gupta, conditions for full-fledged onset will have been satisfied when the shear zone (or the seasonal north-northeast to south-southwest trough) co-exists with what he described as a `broad low' over south Bay of Bengal. This will take some more time to settle, perhaps beyond October 22.

Meanwhile, India Meteorological Department said in its update that only scattered showers could be expected in extreme south peninsula under the influence of the shear zone. A cyclonic circulation is expected to form in the Bay around October 19, said the National Centre for Medium range Weather Forecasting (NCMRWF).

A timeline of five to seven days is what Mr Jim Andrews of AccuWeather.com gives for `a big and lasting shift' to occur in prevailing weather in the south.

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