The Hindu Business Line : Rain surplus shrinks as weak monsoon looms large

Thiruvananthapuram, Aug. 23 Seasonal rainfall surplus has shrunk to three per cent as on Wednesday (August 22) from the five per cent of the previous week under the effect of an intervening weak monsoon phase.

Twenty-nine out of the 36 met subdivisions still returned excess or normal rainfall, with seven posting a deficit (six, last week). But another weak phase is looming large with the western end of the monsoon trough set to retreat again to the north.

The rain-driving trough would now nestle along the western Himalayan foothills. On Thursday, the axis of the trough passed through Pilani, Aligarh, Bahraich, Muzaffarpur, Shanti Niketan and southeastwards to east-central Bay of Bengal.

The retreating trough will cause the rain belt to move to the foothills and further extend to east and northeast India, a signature feature associated with a weak monsoon.

RAINS FOR SOUTHEAST

Fairly widespread rainfall with isolated heavy fall is also likely over the north-eastern States, sub-Himalayan West Bengal, Sikkim and Bihar during next five days, an India Meteorological Department update said on Thursday.

Rain/thundershowers are likely at many places over coastal Andhra Pradesh, the Andaman and Nicobar Islands, at a few places over Telangana during the next 24 hours and increase thereafter.

Rains along the south-eastern coast, including coastal Andhra Pradesh and Tamil Nadu, may scale up soon if projections by the US National Centres for Environmental Prediction are to be believed.

ANIMATED BAY

No major monsoon ‘low’ may be developing in the Bay of Bengal, but the broad ‘troughing’ will leave the basin in an animated state keeping the setting ready for any suitably endowed circulation to strengthen.

Absence of activity concurrently in the west Pacific rules out the possibility of any potent migrant circulation venturing to set up a ‘low’. Local conditions do not suit the formation of an ‘in situ’ system within the Bay either.

Still, the broad trough is expected to stir up some activity along the south-eastern coast as well as over parts of interior peninsula. The NCEP forecasts even suggest the formation of a circulation over the Bay by the weekend (around August 26) whose behaviour will be closely watched. Some clouding was already visible over the west-central Bay on Thursday.

Central and north peninsular India, along with the west coast, will receive good precipitation during the week ending August 30, as per NCEP assessment. The rains will be heavier towards west-central India and the southern fringes of northwest India.

The week starting August 30 and ending in the first week of September when monsoon slips into withdrawal mode over the subcontinent, will also have some rainfall in parts of central India

Wind pattern along the west coast continues to be westerly-to-southwesterly, becoming northwesterly (dry, sinking air) as they approach the extreme southwest coast. In this manner, rainy weather thrown up by the prevailing offshore trough was suppressed towards south Kerala and the peninsular tip.

The upper air cyclonic circulation over northwest Madhya Pradesh and adjoining east Rajasthan had split into two, with one of these leaving drenching rains to parts of west Rajasthan. The other one had drifted into the northeast Arabian Sea and away from the west coast.

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