Buzz of the Southwest Monsoon and its likely approach starts in early May itself. This annual phenomenon drenches large parts of the globe, but it is on the Indian subcontinent that the monsoon casts a spell.  For mainland India, it comes calling in early June and spreads across the landmass in the subsequent 3-4 weeks or so. Sometimes, the monsoon makes an anxious nation wait while it decides to delay its arrival. But then, it may arrive with military punctuality on some other occasions, bringing cheers and raising comfort levels.

The cross-equatorial flow essentially needs to build up for the incursion of the monsoon current. It also means that the trade winds along the equator become strong, cross the equator, and turn clockwise to stream in as southwesterly winds over the Andaman Sea and South Bay of Bengal, to start with. Thereafter, it could maintain a steady pace or may even decide to languidly keep everyone waiting nervously.

The monsoon current arrives over the South Andaman Sea and extreme Southeast Bay of Bengal (BoB) anytime between 15th and 20th May with an error margin of +/- 5 days.

Last year, the monsoon had arrived over that area on 19th May. Further, the monsoon stream advances over the North Andaman Sea and Central BoB by 22nd May. When it keeps its date with the island nation Sri Lanka, the stream penetrates the interiors by 26th May. And the next stop being mainland Kerala, the onset date hangs around 01st June with a standard deviation of about one week.

The conditions are becoming favorable for the advance of the monsoon over the South Andaman Sea and some parts of Southeast BoB between 13th and 15th May 2025. 

There is no powerful system emerging over that area till the middle of May. However, a mild circulation is coming up over the interiors of Thailand, next to the South Arakan Coast of Myanmar. This circulation may enter extreme eastern parts of BoB through the Gulf of Martaban along the Arakan coast, sometimes around 12th May 2025. 

This will accentuate the equatorial flow over South BoB. The strong stream of southwesterly winds will cause heavy rainfall over the Andaman & Nicobar Islands between 12th and 15th May 2025.  This change could mark the entry of the monsoon over the Andaman Sea and Nicobar Islands sometime around 14-15 May 2025.  The initial advancement of the monsoon has no correlation to its further progress over other parts of the ocean and the mainland.