India Meteorological Department (IMD) has been issuing operational forecasts for the date of monsoon onset over Kerala from 2005 onwards. The Southwest monsoon sets over Kerala on June 1 with a standard deviation of about 7 days. The event marks the start of the rainy season over the region and as the monsoon progresses northward, relief from scorching summer temperatures is experienced over the areas. An indigenously developed state-of-the-art statistical model with a model error of ± 4 days is used for this purpose.
The 6 predictors used in the models are: Minimum Temperatures over north-west India; pre-monsoon rainfall peak over south peninsula; Outgoing long wave radiation (OLR) over south China Sea; lower tropospheric zonal wind over southeast Indian ocean; upper tropospheric zonal wind over the east equatorial Indian Ocean, and outgoing long wave Radiation (OLR) over the south-west Pacific region.
The southwest monsoon is expected to set in over Kerala on May 29, 2018 with a model error of ± 4 days.