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Vinson Kurian

Thiruvananthapuram , June 11

Monsoon is likely to revive after June 20 when westerly flows over the Arabian Sea are expected to pick under the influence of two favourable circulatory features on either side of the Indian subcontinent.

While an amplified westerly Madden-Julian Oscillation (MJO) wave is expected to pass into the Indian Ocean region around that time, projections made by the University of Colorado favour cyclogenesis (formation of tropical cyclone) concurrently over the South China Sea. This cyclonic circulation would be ideally placed to consolidate the monsoonal flows into India.

Speaking to Business Line, Dr Akhilesh Gupta of the National Centre for Medium Range Weather Forecasting (NCMRWF) said any monsoon break longer than 15 days will mean that the next pulse breaks out from the Arabian Sea arm only. In which case, the long-drawn onset process and onward progression would have to be re-enacted all over again.

In contrast, a revival triggered by the Bay of Bengal arm would take only two to three days to influence weather over the mainland, but this is unlikely to happen any time soon. Although sea surface temperatures in the Bay are optimum, the high vertical wind shear in the atmosphere aloft does not allow any `low' to take shape.

If vertical wind shear can kill sea-based monsoon systems, its lateral component (lateral wind shear) is seen as aiding cyclonic circulations. In this manner, strong westerly flows between latitudes 15 deg N and 18 deg N can precipitate helpful weather systems.

According to Dr Paul E. Roundy of the University of Colorado, an acclaimed meteorologist specialising in weather over Western/Northeast Pacific and Bay of Bengal, there is a high probability for the South China Sea (bordering Western Pacific) to witness cyclogenesis between June 15 and 18. The south-westerly wind component of this system could trigger the monsoonal flows.

It may be recalled that Dr Roundy had successfully predicted the formation of two Bay of Bengal tropical cyclones, Pyarr and Fanoose, last year.

Projections by the European Centre for Medium-Range Weather Forecasts have also indicated intensification of westerly flows over the Arabian Sea around June 20. But Dr Gupta said these are all too early indications to take a firm view on a likely monsoon revival. Any medium-term forecast on tropical weather beyond seven days is fraught with uncertainty.

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Monsoon revival likely after June 20

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