The commencement of monsoon withdrawal is 11 days late compared to the new normal date set by IMD this year.(Representational Photo/HT Archive)
The commencement of monsoon withdrawal is 11 days late compared to the new normal date set by IMD this year.(Representational Photo/HT Archive)

Monsoon to begin withdrawal today

Till last year the normal date for commencement of withdrawal was September 1 and October 15 for complete withdrawal
Hindustan Times, New Delhi | By Jayashree Nandi
UPDATED ON SEP 28, 2020 01:14 PM IST

Southwest monsoon is likely to begin withdrawing from west Rajasthan on Monday, according to scientists at India Meteorological Department (IMD), who said that conditions are becoming favourable for further withdrawal of the southwest monsoon from some more parts of Rajasthan and Punjab and some parts of Haryana, Chandigarh and Delhi, Uttar Pradesh and Madhya Pradesh in the next two or three days. .

Most of northwest India will witness dry weather hereafter. The commencement of monsoon withdrawal is 11 days late, compared to the new normal date set by IMD this year. As per the new monsoon onset and withdrawal dates issued by IMD in April, the normal date for commencement of monsoon withdrawal from northwest India is September 17 and for complete withdrawal from the country is October 15 . Till last year, the normal date for commencement of withdrawal was September 1 and October 15 for complete withdrawal. IMD’s new onset dates were calculated by scientists in IMD Pune based on analysis of monsoon data from 1961 to 2019 and withdrawal dates are based on data from 1971 to 2019.

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“For the past five years we have been documenting monsoon withdrawal only after September 15. So the dates have changed, which is why new dates were issued by IMD,” said senior scientist Sunitha Devi, IMD, while presenting the weekly weather report on Friday.

Last year monsoon started withdrawing only on October 9 against the normal date of September 1, and the prolonged rain brought a deluge in parts of Maharashtra, Kerala and Bihar in August. Monsoon withdrew completely in only eight days by October 17.

There is a cyclonic circulation over east Bihar and adjoining sub-Himalayan West Bengal and Sikkim and a trough (area of low pressure) from the cyclonic circulation to west central Bay of Bengal off Andhra Pradesh coast across Gangetic West Bengal and coastal Odisha. There is another cyclonic circulation is over south Andhra Pradesh and its neighbourhood. Under the influence of these systems, widespread and heavy rain is very likely over Bihar, sub-Himalayan West Bengal, Sikkim, Arunachal Pradesh, Assam, Meghalaya and coastal Andhra Pradesh during the next 24 hours. Very heavy rain is also likely over parts of Meghalaya in the same period. Dry weather is likely over most parts of northwest India, IMD’s Sunday night bulletin said.

Monsoon rain over the country is 9% in excess since June 1, with 30% excess over south peninsula; 16% excess over central India; a 15% deficiency over northwest India and 7% excess over east and northeast India.

Three main synoptic features are considered for declaration of monsoon withdrawal from the western parts of northwest India—there should be no rain in the region for at least five days, there should be an anticyclonic wind pattern and a considerable reduction in moisture content as inferred from satellite water vapour imageries.

Further withdrawal from the country is declared based on reduction in moisture as seen in the water vapour imageries and prevalence of dry weather for five days, according to IMD.

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