SW Monsoon onset over Kerala likely on June 5
File photo of heavy rains in Kochi, Kerala, on June 9, 2019 a day after the 2019 southwest monsoon arrived in Kerala, marking its onset over the Indian mainland. IANS

SW Monsoon onset over Kerala likely on June 5

New Delhi, May 15, 2020

The onset of the southwest monsoon over Kerala is likely to be slightly delayed till June 5 as compared to the normal date of onset of June 1, the India Meteorological Department (IMD) announced today.

The IMD prediction also gave a model error of plus or minus four days for the onset of the monsoon.

The advance of the southwest monsoon over the Indian mainland is marked by its onset over Kerala and is an important indicator characterizing the transition from hot and dry season to the rainy season. As the monsoon progresses northward, relief from scorching summer temperatures is experienced over the areas.

Southwest monsoon sets over Kerala on June 1 with a standard deviation of about 7 days. IMD has been issuing operational forecasts for the date of monsoon onset over Kerala from 2005 onwards. An indigenously developed state of the art statistical model with a model error of 4 days is used for the purpose.

The six predictors used in the models are the minimum temperatures over North-West India, pre-monsoon rainfall peak over the south peninsula, outgoing long wave radiation (OLR) over south China sea, lower tropospheric zonal wind over the southeast Indian Ocean, upper tropospheric zonal wind over the eastern equatorial Indian Ocean and OLR over the south-west Pacific region.

IMD’s operational forecasts of the date of monsoon onset over Kerala during the past 15 years (2005-2019) were proved to be correct except in 2015 when the actual onset date was June 5 instead of the May 30 forecast.

In the Indian monsoon region, initial monsoon rains are experienced over South Andaman Sea and the monsoon winds then advance in north-westwards across the Bay of Bengal.

As per the new normal dates of monsoon onset/progress, the southwest monsoon advances over the Andaman Sea around May 22. At present, a well-marked Low-Pressure Area lies over southeast Bay of Bengal and neighbourhood.

It is very likely to concentrate into a depression over the same region during next 12 hours and further intensify into a cyclonic storm over central parts of south Bay of Bengal by May 16 evening.

Associated with this event, conditions are likely to become favourable for the advance of the Southwest Monsoon into the Andaman Sea, Andaman & Nicobar Islands and some parts of southeast Bay of Bengal, during the next 48 hours. Past data suggest that there is no association of the date of monsoon advance over the Andaman Sea either with the date of monsoon onset over Kerala or with the seasonal monsoon rainfall over the country.


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