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Vinson Kurian

Thiruvananthapuram May 27 The stage is set for the southwest monsoon to break over Kerala in what is being projected as a strong onset phase spread over the three days from Monday.

The onset is likely to be officially declared during this phase, in which a prevailing deep-seated westerly trough will cause the monsoon current to tag along and make a splash along the southwest coast.

The trough is moving east and will, unusually for this time of the year, bring the rain belt active over Tamil Nadu before becoming irrelevant.

BRIEF LULL

The disintegration of the trough will bring about a lull in the wet weather; but it will get activated once the monsoon current settles and sets up a flow on its own. This is expected to happen around June 2/3, said Dr K.J. Ramesh of the Department of Science and Technology.

The southwest coast has already been brought under the influence of thundershower activity under the influence of the big-amplitude westerly trough. Incidentally, this very trough was blamed for having failed the monsoon during its aborted bid to approach the Kerala coast a few days back.

COPY BOOK STYLE

The cloud build is very good, and propitiously enough, the Easterly Jet has established over the peninsula to provide for a `balance act' by ensuring divergence of flows in the upper levels and convergence in the lower levels. This will make for an onset as close to copybook style as possible.

Meanwhile, the India Meteorological Department has forecast moderate to rather heavy rain at many places over all districts of Kerala, coastal Karnataka and Lakshadweep during the next two days.

Light to moderate rain is also likely to occur at a few places over all the districts of Tamil Nadu, Puducherry, Rayalaseema and south interior Karnataka during the same period coinciding with the movement of the westerly trough to these parts.

MJO DEVELOPING?

According to some international weather models, a Madden-Julian Oscillation (MJO) wave may be developing, which is seen as aiding the orderly evolvement and progress of the monsoon current.

MJO is one of the world's key large-scale atmospheric circulations that regulate the intensity and breaking of rainfall associated with the Indian monsoon. The MJO can be characterised by a large-scale eastward movement of air in the upper troposphere with a period of about 20-70 days, over the tropical eastern Indian and western Pacific Oceans.

The MJO is the main fluctuation of atmospheric circulation that explains variations of weather in the tropics and regulates the monsoon. The variation of the MJO involves variations in wind, sea-surface temperature, cloudiness, and rainfall. MJO is also closely associated with the `break monsoon' phase, usually in July, when monsoon rains stop and re-start.

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Clouds gather as stage is set for onset of monsoon

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