The Hindu Business Line : Land-based ‘low’ to spearhead rains into central parts

Thiruvananthapuram, July 6 A land-based low-pressure area has formed over Jharkhand on Monday, and this would be the pivot around which a reinvigorated monsoon entrenches itself over central India during the rest of the week.

A land-based ‘low’ is not often spoken of in the same breath as a sea-based ‘low’ for analysing comparable strength and rain-generating potential, but that may not always be the case during a monsoon.

The land is awash with moisture during monsoon and this ensures the feed for a ‘low’ to retain the ‘spin,’ says Dr Akhilesh Gupta, lead operational forecaster and Adviser to Ministry of Science and Technology.

Sustained spell

The land-based system, to be followed up by a sea-based counterpart off the Orissa coast by Sunday/Monday, would ensure that the ongoing wet spell continues for another 10 days.

Model forecasts suggests that the first ‘low’ will take a westward course to move into central India, raining heavily all the way across Chhattisgarh, north coastal Andhra Pradesh, Vidarbha, Marathwada and madhya Maharashtra.

Here, the system would accost moisture-laden southwesterlies from the Arabian Sea and is likely to set up a rousing wet spell over western Maharashtra, north Konkan including Mumbai and even south Gujarat.

The ‘low’ would give the lifting motion for the Arabian Sea flows to rain down the contents, and the orography (elevated geographies such as mountains and hillocks) along the way would act as the trigger.

Mumbai rains

Heavy to very heavy rains could once again start pelting Mumbai and surrounding areas from Wednesday afternoon/Thursday morning and could go until the weekend.

Significantly, northwest India could also hope to get some rains as the westerlies from a semi-permanent trough across the border interact with the easterly flows associated with the land-based ‘low’, if not the ‘low’ itself.

Almost the entire northwest India, except extreme west Rajasthan, stand to gain from the intermittent and widely separated rains, Dr Gupta said.

The heavy west cost rains would start lifting only with the formation of a bigger ‘low’ off the Orissa coast early next week as forecast by the European Centre for Medium-Range Weather Forecasts.

And this ‘low’ would bring in incremental easterly flows with oodles of moisture from the Bay of Bengal to set off another wet spell over central India and further to its west.

Available forecasts do not indicate the exact direction — west or west-northwest – of its likely movement into the hinterland. A west-northwest movement would take it careening along the land-based trough from the Bay of Bengal to west Rajasthan.

India Meteorological Department (IMD) said in its update on Monday that the seasonal monsoon trough over land lay extended from Phalodi, Gwalior, Varanasi, Jamshedpur, Digha and southeastwards into the east-central Bay.

MTC WATCH

Dr Gupta said he would still keep a watch-out for a mid-tropospheric cyclonic circulation to spin up high above Gujarat, which could further rev up the rain session over central India and the west coast.

During the past 24 hours ending Monday morning, rainfall occurred at most places over coastal Karnataka, Vidarbha and at many places over east Madhya Pradesh, Jharkhand, Orissa, Konkan, Goa, sub-Himalayan West Bengal, Sikkim, Assam and Meghalaya

The rain-driving offshore trough ran down from south Gujarat coast to Kerala coast, the IMD update said.

Under its influence, active monsoon conditions are likely to continue over the west coast during the next two-three days with further increase in intensity thereafter.

The land-based ‘low’ over Jharkhand will cause fairly widespread rainfall activity with isolated heavy to very heavy falls over east India and adjoining Chhattisgarh during the next two days.

The IMD too was of the view that ‘good monsoon activity’ could be likely on view over central India during the next four-five days with extension into Gujarat and interior Maharashtra from Wednesday.

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