The India Meteorological Department (IMD) had, last year, revised the date of commencement of withdrawal of monsoon from northwest India from September 1 to September 17. Earlier last week, the IMD had said, the withdrawal process may not commence before September 28 or 29.
Rainfall continued in large parts of India driven by two major factors. The monsoon trough lay south of the normal position and continued to remain active throughout the week, while there was development of two low pressure system/cyclonic circulation over Bay of Bengal and its west-north-westward movements.
"(Therefore) conditions are not likely to be favorable for commencement of withdrawal of monsoon from parts of northwest India before middle of the second week (as counted from Thursday)," the IMD said.
"The monsoonal system formation is happening over central India and it causes rainfall till Rajasthan. There should be reversal of winds. For cyclonic monsoon winds, there should be anti-cyclonic winds. That anti-cyclonic winds start from Rajasthan. We should have that circulation at least up to a height of 1.5 km. Also, then come the north-westerly winds to India, these are dry and continental winds. So, there will be no rain," IMD Director General Mrutyunjay Mahapatra said.
Along with this, the conditions should also match about relative humidity and water vapour from atmosphere, when the withdrawal of monsoon from the northwest India commences.
As on Friday, most forecast models are indicating emergence of the cyclonic circulation over Myanmar coast and adjoining areas as a low-pressure area (LPA) over central parts of the Bay of Bengal during beginning of the week. It is likely to move west-northwestwards towards northwest and adjoining west-central Bay of Bengal with no further intensification.
Models are also indicating development of another cyclonic circulation (from remnant of tropical storm Dianmu over West Pacific) over east-central Bay of Bengal during the second half of this week with west-northwestwards movement towards northwest Bay of Bengal and no further intensification, the IMD said.
Meanwhile, during the week ending on September 22, above normal rainfall activity was reported over India and weekly cumulative All India Monsoon Rainfall departure from its long period average (LPA) during the week was 28 per cent. "This is the 3rd consecutive week when above normal rainfall activity continued for India as a whole," the IMD said.
Weekly all India percentage departure from LPA for last three weeks i.e., for week ending on September 9, September 16 and September 23 are 15 per cent, 53 per cent and 28 per cent while the all-India seasonal monsoon rainfall departure from its LPA, for the period from June 1 till September 22, has improved to minus 3 per cent from minus 9 per cent, which was the situation till September 1, the IMD data has showed.