Monsoon awaits its next ‘pulse’ in Bay of Bengal

After making a timely onset two days ago, the Bay of Bengal arm of the monsoon is waiting for the next ‘rain pulse’ to give it a fresh momentum and cover more parts of the Bay.

The India Met Department (IMD) does not air concern here, and has maintained that conditions are favourable for its further advance into more parts of South Bay, the North Andaman Sea and the Andaman Islands over the next two to three days.

A cyclonic circulation each over the South Andaman Sea to the extreme East and over the Comorin to the West-South-West are keeping a vigil to sustain the momentum across the waters. Another one hovers above South Tamil Nadu and Gulf of Mannar.

Wait on other side, too

A shear zone of monsoon turbulence in the higher levels of the atmosphere across extreme South Sri Lanka provides the monsoon a safe haven with the circulation over the Comorin embedded into it.

To the West, the Arabian Sea arm is counting on an itinerant Madden-Julian Oscillation (MJO) wave to help with the all-important onset over Sri Lanka and subsequently along the Kerala coast over mainland India.

The periodic MJO wave of a band of lower-pressure travelling West to East above the Equator is responsible for setting up low-pressure areas, depressions and even cyclones as well as the onset of monsoon along its path.

The MJO wave has alternating dry and wet phases; a wet phase has long passed it, and is now expected to enter the West Indian Ocean (South Arabian Sea) later this week.

MJO dry phase on

Currently, a dry MJO phase lords it over over the West Indian Ocean. It does not allow clouds to form and suppresses rainfall. It will stay as such until the weekend, the Climate Prediction Centre (CPC) of the US National Weather Service has said.

But the anticipated arrival of a wet MJO phase also bristles with the prospect of cyclone genesis, as was the case a week ago when the precedessor wave set up twin cyclones in the West Pacific (‘Lili’ and ‘Ann’), delaying its progress.

Given this, models do not rule out the possibility of the MJO wave on return causing monsoon flows to converge in the Arabian Sea and set up later in May/early June a low-pressure area, its intensification and track away to Yemen-Oman.

This has happened often in the past and hit the onset progress of the monsoon over India. Sources said it is likely that the IMD would have factored it in while announcing the date of onset of Kerala on June 6, ‘slightly’ delayed this year as it put it.

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