The Hindu Business Line : `Low' over Bay strengthening

THE pre-existing upper air circulation over south of Bengal has strengthened into a low-pressure area on Sunday, which is expected to further boost up the rainfall activity over parts of Tamil Nadu, south interior Karnataka, Telengana, Kerala and coastal Andhra Pradesh.

The system is seen organising itself slowly into a well marked `low' and move very slowly in a westerly/northwesterly direction during the coming days, said Dr K. J. Ramesh of the National Centre for Medium Range Weather Forecasting (NCMRWF).

He told Business Line that there did not exist a precedent in which the onset of northeast monsoon is formally declared. But if `sustenance' of rainfall were to be the critical factor influencing a decision, the latest rainfall pattern emerging from the eastern flank of the southern peninsula could weigh in heavily.

According to a NCMRWF weather update, rainfall over the past 24 hours ending Sunday morning has been of fairly widespread in nature with isolated heavy showers over parts of Tamil Nadu and Pondicherry, Lakshadweep and south interior Karnataka. Significant amounts of rainfall were recorded at Nagapattinam (11cm); Karaikal (9 cm); Tondi and Thanjavur (7 cm each); Bangalore, Thiruchirapalli and Chitradurga (6 cm each) and Agathi (5 cm).

As per earlier assessments, the movement of the `low' from the south Bay towards the east coast of peninsular India will go to further consolidate weather conditions leading to the full-fledged onset of northeast monsoon over Tamil Nadu and adjoining States. Given this scenario, the enhanced level of rainfall activity over Tamil Nadu and the adjoining region will likely be maintained during the coming days as well.

Meanwhile, the retreat of southwest monsoon from the remaining and Maharashtra has been stalled due to the strengthening of the circulation over the south Bay. The southward shift of the anti-cyclone with a core of south easterlies also has ceased, by default aiding the strengthening of the northeasterly monsoon winds.

Model predictions indicate that the hilly regions of Himachal, Uttaranchal and Jammu and Kashmir will experience isolated to scattered rainfall activity during the next 3-4 days due to the prevalence of an upper air cyclonic circulation over Himachal Pradesh and neighbourhood. A similar circulation over east Uttar Pradesh and adjoining Bihar is likely to induce isolated to scattered rainfall over parts of Bihar for the next 1-2 days.

In region-wise forecast, the NCMRWF said that sub-Himalayan West Bengal and Sikkim are likely to experience isolated spells of rain while Orissa, Gangetic West Bengal and the Northeastern will experience scattered to fairly widespread rains in the coming days.

Tamil Nadu, south interior Karnataka, Rayalaseema, parts of Telangana, Kerala and coastal Andhra Pradesh are likely to experience scattered to fairly widespread rainfall with spells of heavy rainfall activity in some areas. Islands over the Bay of Bengal and the Arabian Sea also are expected to receive scattered rains for next 1-2 days. Isolated rainfall activity is expected over rest of the regions.

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