The onset of Southwest Monsoon is a seasonal event. Over the Indian sub-continent, Kerala sees the arrival of Monsoon around June 1 wherein a normal variation of a week is commonly seen.
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There are several factors that influence the onset as well as the progress of Monsoon. The onset of Monsoon needs triggers in the form of a variety of weather systems. These weather systems are seen in the Monsoons season which are mostly ocean borne to activate the Monsoon surge.
The first one is the low-pressure area or a depression in the Bay of Bengal which forms in the Bay during the last few days of May or the beginning of June.
Similarly, there are low pressure areas in the Arabian Sea which can pull the Monsoon current forcing it to Kerala ushering Monsoon into the region.
The third factor is the cyclonic vortex which is more closely marked than the usual cyclonic circulation off the Kerala coast and is associated with cloud mass.
The fourth factor is the trough along the West Coast due to which rain is seen increasing and the intensity of winds also sees a rising trend.
Lastly, the cross-equatorial flow of winds is another factor which is responsible for the onset of Monsoon. Significant cross equatorial flow of winds wherein winds from the Southern Hemisphere cross to the Equator becoming southwesterly. A significant cross equatorial wind pattern is quite capable of bringing a strong Monsoon surge towards the Indian mainland.
Image Credit: Times Now
Please Note: Any information picked from here must be attributed to skymetweather.com