Monsoon or pre-monsoon? ETA not too sure this year

BENGALURU:  Has the southwest monsoon arrived? While experts and weathermen forecast that the monsoon will hit the mainland early this year, even ahead of its scheduled onset of May 27, some officials say it has already set in, but not yet announced.  “The factors which lead to the onset of the monsoon show that these showers are not pre-monsoon, but monsoon itself. However, the Centre is yet to announce it,” said an IMD official.  

IMD says that due to the presence of very strong systems in the Arabian Sea and Bay of Bengal, rain has intensified. Experts say the monsoon arrives early due to many factors, which are already in place.  Prof J Srinivasan, scientist, Divecha Centre for Climate Change, said that onset of monsoon is due to systems forming in May, which is happening at present. It is also because of the Pacific Decadal Oscillation (a variability of sea surface temperature of the North Pacific Ocean that varies at multi-decadal times), which is negative now. This with the La Nina effect, can bring higher rainfall. 

Dr Arindam Chakraborty of Centre for Atmospheric and Oceanic Sciences, IISc, said for the early monsoon, there should be sufficient moisture.  A close look will reveal heavy rain in the northeast, cyclone Asani, formation of weather systems, and sufficient moisture in the South — all contributing to an early monsoon, if these systems continue, he said.