Forecast of the Onset Date of Southwest Monsoon - 2019 over Kerala
Southwest monsoon sets over Kerala on 1st June with a standard deviation of about 7 days. The event marks the start of rainy season over the region and as the monsoon progresses northward, relief from scorching summer temperatures is experienced over the areas. India Meteorological Department (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 6 Predictors used in the models are; i) Minimum Temperatures over North-west India, ii) Pre-monsoon rainfall peak over south Peninsula, iii) Outgoing Long wave Radiation (OLR) over south China Sea, (iv) Lower tropospheric zonal wind over southeast Indian ocean, (v) upper tropospheric zonal wind over the east equatorial Indian Ocean, and (vi) Outgoing Long wave Radiation (OLR) over the south-west Pacific region.
IMD’s operational forecasts of the date of monsoon onset during the past 14 years (2005-2018) were proved to be correct except in 2015. Forecast verification for the recent 5 years (2014-2018) is given in the table below.
2. Advance of monsoon over the Andaman Sea
Conditions are becoming favourable for advance of southwest monsoon over the southern part of Andaman Sea, Nicobar Islands and adjoining southeast Bay of Bengal during 18-19th May 2019. Past data suggests 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.
3. Forecast for the 2019 Monsoon Onset over Kerala
This year, the statistical model forecast suggests that the monsoon onset over Kerala is likely to be slightly delayed. The southwest monsoon onset is likely to set over Kerala on 6 th June with a model error of ± 4 days.