The Hindu Business Line : Bay system may remain stationary

The fresh `low' over north Bay of Bengal off the north Orissa-West Bengal coast became well marked and persisted on Friday, as a resident low over southwest Madhya Pradesh showed signs of re-intensification.

The National Centre for Medium Range Weather Forecasting (NCMRWF) said that the resident low has too become well marked amid apprehensions that a mid-tropospheric cyclone (MTC) may be building over neighbouring Gujarat.

BIDDING TIME

No two distinct lows can operate concurrently over land and this might explain why the Bay system is bidding time to cross over into land.

But an MTC is known to co-exist with a prevailing monsoon system and can even interact to create torrential rainfall, like they did in July 2005 and set off the Mumbai deluge.

NCMRWF said that model predictions suggest that the Bay system is likely to remain near stationary and intensify in the next 24-36 hours while moving slowly in a west-northwest direction. Under its influence, widespread rainfall with heavy to very fall is likely over Orissa, coastal West Bengal and north coastal Andhra Pradesh.

TO SCALE UP

Subsequently, rainfall is seen scaling up with scattered heavy to very heavy fall and isolated extremely heavy rainfall covering Orissa and north coastal Andhra Pradesh from Sunday. It might then extend into Chhattisgarh and Telangana.

On the other hand, the resident low is forecast to trigger widespread rainfall with heavy to very heavy fall at a few places over Gujarat region, southeast Rajasthan and southwest Madhya Pradesh and isolated showers over Saurashtra, Kutch, Konkan and Goa during the next two days.

SHORT BREAK

The session may taper off over Gujarat, southeast Rajasthan and southwest Madhya Pradesh only to return within the next 24 hours with scattered heavy to very heavy rains over Saurashtra, Kutch, Konkan and Goa (including Mumbai) from Sunday onwards.

Monsoon is likely to remain active over central and Peninsular India during next week, the NCMRWF said.

Low of depressions

Low-pressure areas (lows) during monsoon are but logical conclusions thrown up by the larger monsoon trough settling into place over land and jutting into the sea (the Bay of Bengal).

Viewed from a strictly meteorological point of view, lows are not a significant weather phenomenon, said Dr Akhilesh Gupta of the Department of Science and Technology.

What meteorologists are keen to watch is the calibrated intensification of a low into being well marked and later into full-blown monsoon depressions.

Depressions drive monsoon inland and ensure the even spread of precipitation. It is the progressively increasing pressure differential relative to the surroundings that sets up a low, which grows to become depressions, deep depressions, tropical storms and cyclones.

The low features loose-binding clouds, which become more organised and concentrated with intensification.

On-rushing air into the core of the system sets up accompanying winds. High wind speeds means enhanced convection and moisture influx, and therefore greater precipitation.

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