Met sees surplus ‘reverse’ monsoon for South

The South-West monsoon has exited the country 19 days after the normal date, an India Meteorological Department update said on Monday.

This clears the way for the North-East monsoon over the five Met subdivisions in the South of the country; but the onset has already been delayed beyond the normal May 15-20 timeline.

Surplus monsoon The Met has forecast a surplus North-East monsoon during the October-December season this year with rainfall expected to be 11 per cent above the long-period average (33 cm).

The five Met subdivisions covered by the North-East monsoon are Tamil Nadu, Coastal Andhra Pradesh, Rayalaseema, Kerala ad South Interior Karnataka.

The seasonal rainfall for Tamil Nadu is most likely to be above normal 12 per cent above the long period average of 43.8 cm (base period being 1951-2000), the Met said.

The probability of an above normal North-East monsoon season rainfall over the South Peninsula and over Tamil Nadu is 88 per cent and 90 per cent respectively.

The five Met subdivisions receive about 30 per cent of its annual rainfall during the October-December season. Tamil Nadu in particular receives about 48 per cent of its annual rainfall during this period.

Riding El Nino In this manner, the North-East monsoon is expected to ride the El Nino on the Pacific that has even in the past returned good rainfall for South Peninsular India without direct cause-effect relationship. The Met bulletin on Monday did not, however, say as to when the North-East monsoon would set in over Peninsular India.

What it did say was that the South-West Monsoon has withdrawn from remaining parts of East and Northeast India, Peninsular India, the Bay of Bengal and the Arabian Sea.

In recent years, its exit and the entry of the reverse monsoon (North-East monsoon) have taken place simultaneously.

This year, two raging typhoons (‘Koppu’ and ‘Champi’) in the Northwest Pacific have sent the wind flows over upstream Bay of Bengal into disarray, upsetting the Met applecart.

Winds in disarray The winds are weak north easterlies over the Bay currently, but it will not be long before they are reversed to being south-westerly under the influence of the typhoons.

A welcome change is expected to happen around Monday when the south-westerlies flows turn around over the Gulf of Thailand to form a cyclonic circulation and reverses flows to being easterlies.

A couple of other circulations are also expected to form over the Northeast Bay of Bengal off Myanmar and also to the south-east of Sri Lanka, both of which are ideally positioned to trigger the North-East monsoon.

Under their influence, the rains may set in over Sri Lanka and adjoining south-east Tamil Nadu towards the end of the month, according to global forecasts.

But most of Tamil Nadu and the rest of adjoining peninsula, except Kerala, are expected to witness deficient rainfall right until the month-end, these forecasts say.

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