Bay of Bengal waters are boiling with sea-surface temperatures of 32℃ and above, but a stubborn anticyclone sitting heavy atop has not allowed it to breathe free and conjure up the first pre-monsoon low-pressure area even as April gives way to May, and scheduled date for arrival of monsoon over mainland India is not too far away. 

A pre-monsoon ‘low’/depression drags the Inter Tropical Convergence Zone (ITCZ), the rain belt around the globe, into place over Southern and Central Myanmar by May 18 to climatologically signal the onset of the South-West monsoon, and 10 days later (May 28) over Northern Myanmar. But there is no system on view yet to jumpstart these procedures one after the other. 

Delayed over Myanmar

The Myanmar national forecaster has gone on record saying the monsoon is likely to set in over the country between June 9 and 14, indicating a a delay of at least 20 days. What impact this could have on customary follow-up onsets over Andaman & Nicobar Islands (May 18-20), first port of call in Indian territorial waters, and over Sri Lanka (around May 22), will bear some watching. 

The monsoon reaches mainland India over Kerala within a week of precipitating the onset over Sri Lanka. Last year, it arrived over the Andaman & Nicobar Islands around the normal time despite being delayed over Myanmar by more than a fortnight. Latest Myanmarese outlook for a pre-monsoon ‘low’ to settle over the Andaman Sea and South Bay by Friday is most likely to fail. 

Above-average monsoon

Late or early onset does not have anything to do with monsoon performance during a given season. This year, it is widely expected to ride the wings of a brewing La Niña in the East-Equatorial Pacific likely coupling itself with a positive phase of the Indian Ocean Dipole (IOD). India Meteorological Department (IMD) has already predicted an above-average monsoon. The Myanmar national forecaster says the monsoon will be weak to moderate during the ‘early monsoon period’ till June-end. It expects two low-pressure areas to form over the Bay of Bengal, of which one may further intensify into the depression. 

Forecast of low-pressure systems

The ‘mid-monsoon period’ starting from July 1 to the end of August may see three ‘low’s over the Bay. Two of them may intensify into depressions during when the monsoon will be moderate to strong. The ‘late monsoon period’ starting from September 1 till the date of withdrawal too may witness three ‘low’s form over the Bay, of which one may further intensify into a depression. 

The Sri Lankan Met department says atmospheric disturbances, low-pressure systems or cyclones may develop in the vicinity of the island during the latter part of May. There is a higher chance for above normal rainfall over Western, Southern, Sabaragamuwa, Central and Uva provinces and near-normal rainfall over remaining areas of the country during the month. As for June, there is a higher chance of above normal rainfall for the south-western Sri Lanka and near normal rainfall elsewhere in the country. There is a chance of most parts of the country having normal rainfall during July, the agency said.