Cyclones in West Pacific delaying monsoon over mainland India

The onset of the monsoon over Kerala is being delayed mainly by an ongoing suppressed phase of the Madden-Julian Oscillation (MJO) wave, says the Climate Prediction Centre (CPC) of the US National Weather Service.

But it also added that the convection (the process of cloud-building and rainfall) may begin to increase during the last week (May 22 to 28) of the month.

GLOBAL BAND

The MJO wave is a global band of low-pressure area packed with convection and rainfall passing from West to East around the Equator periodically and has alternating dry and wet phases.

The wet phase has been known to trigger low-pressure areas, depression or even cyclones and also underwrite monsoon onsets under its footprint as it travels from West to East.

Currently, a dry phase with suppressed rainfall features is active over the Indian Ocean, which is expected to last well into the last week of May.

This is because a preceding wet phase has been unduly delayed over the West Pacific due to a pair of cyclones of its own making, according to the CPC.

There is also a concern that another cyclone could develop as the MJO wave enters the East Pacific into the last week of May, further delaying its journey.

MONSOON PROGRESS

Hence below-average rainfall is the take for much of South-East Asia and the West Pacific during this week, though a decrease in coverage of the dry area is indicated for the last week as the wet MJO phase returns.

Meanwhile, a day after India Met Department (IMD) announced the arrival of the monsoon over the South Andaman Sea and parts of the South Bay of Bengal, its northern limit remains unchanged.

The northern limit represents a line linking the exact coordinates where the monsoon has progressed since the onset in its journey to cover the Bay, the Arabian Sea and mainland India into June.

This line did not touch any and feature except Car-Nicobar, and lay extended from the Indian Ocean ro the South of Sri Lanka to the South-East Bay just to the West of the Andaman Islands.

But the IMD assessed that conditions are favourable for further advance of the monsoon into more parts of the South Bay, the North Andaman Sea and the Andaman Islands during next three days.

MYANMAR ONSET

The monsoon flows represent robust wind flows from South of the Equator instigated by the sustained heating of the land (mainland India) and creation of lower pressure compared to the adjacent seas.

On Sunday, the Myanmar Department of Meteorology and Hydrology announced that the monsoon would hit the southern parts of the country between Tuesday and Thursday.

Myanmar lies to the North-North-East of the Andaman & Nicobar Islands and is the second major milestone in the northward progression of the monsoon, ahead of the penultimate pit-stop of Sri Lanka.

The Myanmar Met saw a largely moderate monsoon, and also indicated that a low-pressure area may form over the South Bay to boost the monsoon flows.

The IMD too seemed to agree, and its wind-field projections showed a cyclonic circulation loitering around the seas South of Myanmar by May 28. This is aside of a circulation currently hovering over the Andaman Sea.

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