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Shifting trough set to lift rains in east, northeast

Vinson Kurian

Thiruvananthapuram, July 30

The India Meteorological Department (IMD) has officially put northwest and adjoining west-central Bay of Bengal under the radar for a low-pressure area expected to brew from August 4.

An IMD forecast confirmed that a preparatory upper air cyclonic circulation could start descending to lower levels to set up the `low.' This will decisively bring the `break monsoon' phase that lasted more than a fortnight to an end.

This `low' would secure the south-eastern tip of the rain-driving monsoon trough and help it to realign along a southerly perch to represent full-blown monsoon conditions once again over the landmass.

RAINS TO LIFT IN EAST

Currently nestling along the Himalayan foothills, this trough was responsible for bringing inundating rains to east India as well as the North-Eastern States.

These rains are expected to subside as the trough takes leave of the region.

On Monday, the axis of the trough passed through Ganganagar, Karnal, Hardoi, Gorakhpur, Darbhanga, Dhubri and thence eastwards to Arunachal Pradesh.

A southward shift of the rough, expected to start from Thursday, will bring the Arunachal-end to dip into the centre of the low pressure in the Bay.

This will help `switch' the monsoon back into `on' position.

In this manner, the IMD update said, rains will return to central and adjoining peninsular India.

These areas had dried up from mid-July, contributing to the slide in surplus rain quantum from a peak of 20 per cent to four per cent as on July 25.

`LOW' MAY INTENSIFY

Projections by the European Centre for Medium-Range Weather Forecasts (ECMWF) continue to suggest an active phase of monsoon enveloping central and peninsular India at least for a week beginning Saturday.

The westerly flows will ensure that the `low' in the Bay intensifies in tandem into a monsoon depression.

Another low-pressure area is projected to be tossed up over the northeast Arabian Sea, off the Gujarat coast, through mid-week.

Initial assessment is that it would move east and cross the Gujarat coast, but this needs confirmation.

In any case, weather systems on either side of the peninsula would represent a most potent phase of the monsoon.

FRIENDLY PACIFIC

The reviving monsoon would have to contend with two major systems developing in the South China Sea and the Philippine Sea, which lie to the east of the Bay of Bengal.

But, unlike Typhoon Man-Yi, which sped away to the north-east shutting down the Indian monsoon earlier, these systems are seen moving in a north-northwest direction.

This is so because the high-pressure area building in the equatorial and east Pacific in the wake of the prevailing typhoon, named Usagi, will prevent them from moving in a north-eastern direction.

Northwest-bound Pacific systems, on the other hand, do not unduly harm the Indian monsoon.

Meanwhile, numerical weather models on Monday suggested widespread rainfall activity with isolated heavy to very heavy falls in the North-Eastern States and Gangetic Plains during the four days.

An offshore trough will bring fairly widespread rainfall with scattered heavy to very heavy fall along the west coast.

Fairly widespread rainfall activity is also likely over extreme south peninsula during next three days.

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