has been quite accurate in predicting the onset date. In the last 14 years, actual onset date was incorrect only in one instance.
Experts and scientists from the IMD
said that a delayed monsoon arrival has no bearing on the advance of the southwest monsoon
over the entire country or its regional spread. Progress of sowing or agricultural output cannot be predicted or surmised from onset date either.
Current thermal circulation and convective patterns over northern and northwest India are dominated by western disturbances among others. This condition is not conducive for formation of a pressure gradient pulls the winds flowing north of the equator to India from the southwest direction.
The met department has been issuing operational forecasts for the date of monsoon onset over Kerala from 2005. An indigenously developed statistical model with a model error of ± 4 days is used for the purpose.
The model uses six parameters to get the probable onset date. They are: minimum temperatures over northwest 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 OLR over the south-west Pacific region.