Our Bureau

Thiruvananthapuram , Sept. 25

THE dominant western disturbance has assumed complete sway over the prevailing but rapidly weakening `low', lugging it to the eastern and northeastern parts of the country.

On Saturday, the `low' was located to northeast Rajasthan and adjoining southwest Uttar Pradesh and southeast Haryana. The western disturbance had dragged the system further northeastward overnight, bringing it to a perch over west Uttar Pradesh and adjoining Uttaranchal.

An update by the National Centre for Medium Range Weather Forecasting (NCMRWF) on Sunday said the associated upper air cyclonic circulation extended up to 4.5 km above sea level. The system is likely to move further east-northeastwards. During the 24 hours ending Sunday morning, fairly widespread rainfall with very heavy falls was reported from Uttaranchal. The wet weather has reduced significantly to the northwest, i.e. over Gujarat, Konkan, Goa as also coastal Andhra Pradesh, where scattered light to moderate rainfall was reported.

Moderate rainfall has also occurred over east Rajasthan, Haryana and west Uttar Pradesh. Chief amounts of rainfall (in cms) are: Nainital-22, Mukteshwar-18, Gangtok-14, Pithoragarh and Pantnagar-11 each, Port Blair-9, Dehradun and Tehri-7 each, Delhi (Palam) and Hut Bay-6 each, Tirupathi-5 and Jaipur and Chennai-4 each.

As is normal when the axis of monsoon trough starts migrating to the east, Tamil Nadu will get to experience isolated rains over the next 2-3 days. Model prediction suggests that the movement of the low-pressure system towards east will leave the place open for the anti-cyclonic circulation that has been lurking in the background at the 700-millibar levels (3.1 km above sea level). This could lead to resumption of the process of withdrawal of monsoon from the north and the northwest from September 30 onwards.

It may be recalled that the anti-cyclone had come to establish its presence with the monsoon exiting extreme Rajasthan earlier this month. The status quo ante was broken only by a migrating system from the western Pacific that first set up a cyclone in the Bay of Bengal. It crossed land as a deep depression and propagated itself progressively as a low-pressure system into central and northwest India.

This triggered the monsoon easterlies and westerlies that brought wet weather back that has come to hold to this day. The western disturbance intervened lately, which is responsible for shifting the area of convection to the east.

Due to ongoing interaction of the above systems, enhanced rainfall activity with heavy to very heavy falls is likely to continue over Himachal Pradesh, Uttaranchal and West Uttar Pradesh for the next 24-36 hours. This will extend eastwards to east Uttar Pradesh, Bihar, Jharkhand and the Northeastern States in due course.

Isolated to scattered rainfall are likely over the western region except west Rajasthan where mainly dry weather is likely to prevail during the next 3-4 days. There may be increase in rainfall activity over Konkan and Goa after two days.

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