Vinson Kurian

Thiruvananthapuram, Nov 24

WEDNESDAY'S `low' over southern Tamil Nadu and neighbourhood sped its way west to cross Kerala overnight and position itself over southeast Arabian Sea on Thursday afternoon in line with predictions.

Associated upper air cyclonic circulation extended up to mid troposphere, said Dr L.S. Rathore of the National Centre for Medium Range Weather Forecasting (NCMRWF). The system is likely to keep moving in a westerly direction, while steadily losing in strength.

Meanwhile, north India is bracing to host what Dr Rathore described as the first major western disturbance of the season that is expected to drive harsh winter weather to three major States and the plains of the region from early next week.

Referring back to peninsular weather, he said fairly widespread rains with isolated heavy falls would continue to lash Tamil Nadu, Pondicherry, Kerala and Lakshadweep for another two-three days at the least. According to forecasts by the NCMRWF, the rains will be scattered in Rayalaseema, south interior Karnataka and coastal Karnataka during this period. Isolated rains are expected over south coastal Andhra Pradesh.

The `low' is poised to merge into the larger east-west shear zone of monsoon turbulence covering south Bay of Bengal, the southern parts of the mainland and the south Arabian Sea. This will bring a temporary lull to the proceedings over land with the rainfall reducing in intensity. But the shear zone itself is expected to remain active for the next four days as well.

But the NCMRWF maintained its outlook on a fresh cyclonic circulation taking shape over southeast Bay of Bengal during the next 24-48 hours. The system is seen moving westwards and is expected to influence south peninsular weather after Sunday.

According to model projections by the European Centre for Medium-Range Weather Forecasts (ECMWF), the shear zone is seen reactivating a low-pressure area over the southwest Arabian Sea by Monday. This will bring the second engine of the northeast monsoon roaring to life once again. The fresh circulation over the Bay on the eastern flank will have taken shape almost simultaneously, which is expected to move west towards the peninsular coast.

This scenario could possibly lead to the unfolding of another wet session over the peninsula during the coming week.

Cold wave in North: North India will wake up to chilly weather with rain/sleet as it accosts the incoming western disturbance, the biggest yet of the season, by Sunday. According to Dr Rathore, this low-pressure system originating somewhere from the west Atlantic/Mediterranean Sea will likely intensify over the two subsequent days and cause intense rainfall/snow over Jammu and Kashmir, Himachal Pradesh, Uttaranchal and even the plains of northwest India.

This will have a major impact on the winter in North India, with the mercury expected to fall appreciably, thanks largely to the northwesterly winds expected to follow in its wake.

The westward shift of the prevailing anti-cyclone (now located over central-west Arabian Sea and further west) has helped redefine the cold westerly flows since the eastern flank of the system is pre-disposed to the prevailing northwesterlies. This explains the strength of the western disturbance as it approaches Jammu and Kashmir, Dr Rathore added.

(This article was published in the Business Line print edition dated November 25, 2005)
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