As the Arabian Sea arm of the monsoon prepares to unleash a smash along the West Coast later this week,  counterpart Bay of Bengal would be hardly found wanting.

This is because the enhanced phase of the Madden-Julian Oscillation (MJO) is  sitting pretty over the East Indian Ocean (just to the Bay's South) providing ample support from the higher levels.

WET, DRY PHASES

The MJO wave packs clouds, moisture and heavy rain as it passes high periodically over the Indian Ocean region from West to the East with alternating 'wet' and 'dry' phases.

It has profound influence on ground level weather under its footprint - the wet phase triggers storms and monsoon onsets while the dry phase suppresses rainfall, unleashing break-monsoon.

From its base over West Indian Ocean last week , it had triggered back-to-back cyclones 'Sagar' and 'Mekunu' in the adjoining Arabian Sea and also overseen the onset of the monsoon over Kerala.

Its arrival over the East Indian Ocean is being closely monitored for implications for the Bay. Global models concur that a strong low-pressure area is there for the asking.

But they doubt if it can grow beyond the depression/deep depression level, since high wind shear during the monsoon inhibits the growth of the storm tower. 

VIGOROUS STATE

Still it is enough to set off quite a churn in the Bay and help bring about a vigorous phase of the monsoon not just in the seas but also over land.

The US Climate Prediction Centre (CPC) said that the MJO would make an elaborate but slow movement across the East Indian Ocean and adjoining Bay over the next couple of days.

It would exit the Bay only after switching it fully into active mode and leaving it with enough traction to keep the waters in an animated state into the next week.   

The CPC said that significant rain is expected over East India, the Bay basin, and pars of Bangladesh and Myanmar, with a low-pressure area forming South-West of Bangladesh and South of Kolkata in India. Regardless of whether is is classified as a tropical cyclone (deep depression at best, given the monsoon environment), the entire region will experience above-average rainfall during this week.

Meanwhile, the MJO wave would travel from East Indian Ocean into the North-West Pacific, setting off a churn and likely coming up with a typhoon (cyclone) there.

PACIFIC STORM ALERT

In advance, the US Navy Joint Typhoon Warning has already upgraded the status of a tropical depression to the South-East of Da Nang, Vietnam, to that of a minimal cyclone.

The US agency is also tracking two other systems (90W and 91W) with 'medium' and 'high' prospects of growth to the next level in the short to medium term.

Currently, these three systems are also helping to draw in the south-westerly monsoon current across the South Arabian Sea, the Bay of Bengal and the South China Sea.

All these are covered by a single South-West monsoon system concurrently and they help each other to benefit from the flows so long as they are churning within the basin.

Any track away to the East China Sea, North-Central Pacific or Sea of Japan would weaken the system, with India situated to extreme East likely suffering the most.

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