The southwest monsoon is expected to arrive ahead of time this year, hitting Kerala on May 30 according to the India Meteorological Department. The normal date of the onset of monsoon in the country is June 1. Even as the long range forecast issued last month has stated below normal rainfall, the onset of monsoon is ahead of time according to IMD officials. The monsoon is likely to arrive with a model error of plus or minus four days, the IMD stated.
The advance of the southwest monsoon over the Andaman Sea normally takes place around May 20 with a standard deviation of about one week. During the last few days, enhanced convection and increased rainfall activity has been observed over the Bay of Bengal and the Andaman Sea. The IMD has stated that the cross equatorial flow is likely to strengthen and deepen over the area. As such, conditions are becoming favourable for advance of the monsoon over the Andaman Sea and adjoining sea areas during the next 3- 4 days.
[Watch video below]
Past data suggests absence of any one-to-one association of the date of monsoon advance over Andaman Sea with the date of monsoon onset over Kerala or that with the seasonal monsoon rainfall over the country. The onset of monsoon is the deciding factor for the state to put forth a contingency plan as the country is expected to face a monsoon deficit.
From 2005 onwards, ESSO-India Meteorological Department (IMD) has been issuing operational forecasts for the date of monsoon onset over Kerala using an indigenously developed statistical model, which uses the following six predictors – Minimum Temperature 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 over south-west Pacific region.
The timely onset of the monsoon is crucial for the sowing of kharif crops like paddy and a deficit in rainfall may hit the rice output.