Heavy rains likely for Bay, east from mid-June

Heavy monsoon rains are projected to buffet the southern three-fourths of the country during a two-week phase starting from June 15, according to latest international weather model projections.
Outgoing long-wave wave projections, a proxy for cloud cover, suggest that the heaviest rains may unfold over Bay of Bengal and adjoining eastern parts of the country during this period.

WET MJO WAVE


All this would result from a renewed wet phase of the Madden-Julian Oscillation (MJO) wave that periodically transits the upper levels of the atmosphere above equatorial Indian Ocean.
The MJO wave has profound influence over weather on ground, especially during monsoon. The last active wet phase of the wave around May 25 saw the monsoon making an onset five days ahead of normal over Sri Lanka.
The south-west coast of India just to the north should also have normally witnessed the onset almost immediately after, but had to sit out thanks to a concurrent tropical cyclone ‘Laila' in the Bay of Bengal that pumped away available moisture.
By the time ‘Laila' blew over, the alternating ‘dry' phase of the MJO wave had set in, affecting the convection pattern, moisture build, wind profile and direction in the Arabian Sea.
The eastward-progressing active MJO wave has since brought South-east Asia and parts of the West Pacific under its influence. Alternating suppressed convection is likely to progress northward across India into early June.

FRESH CONVECTION


Fresh convection has begun to engulf south and adjoining east-central Arabian Sea thanks to the very warm seawaters.
The winds are also seen falling into the ideal pattern but the present convective state around the global tropics is not dominated by the wet phase of the MJO wave.
This is what has led experts to fear that the onset, expected to happen over the next two days as indicated by India Meteorological Department (IMD), may not sustain.
The IMD projects the formation of a monsoon vortex (an intense low-pressure area that is known to trigger the onset) in the Arabian Sea. But according to experts, a vortex is not generally independent from the MJO in true onset cases, although such vortices may develop occasionally without MJO support.

NEXT WAVE


The next wet MJO wave would not set in until the end of the first week of June, according to various model outlooks. The intervening period would see a low-pressure area spinning up over east-central Arabian Sea, which would intensify to become a likely tropical cyclone and track west-northwest.

The Oman coast and the southwest Gujarat coast are variously predicted to be the landfall areas depending on whether an incoming westerly trough keeps date.
If the latter is indeed the case, the cyclone would be swung east in line with the movement of the westerly trough and dumped over the Gujarat coast.
The European Centre for Medium-Range Weather Forecasts , among others, has consistently pointed to this probability during the last six model runs.
Meanwhile, on Sunday, the IMD said in its update that conditions have become favourable for the onset over Kerala during the next two days.
Satellite imagery on Sunday afternoon showed convective clouds over parts of east-central Bay of Bengal, Andaman Sea and south and adjoining central Arabian Sea. Forecast until Wednesday suggested fairly widespread rain or thundershowers over Andaman and Nicobar Islands, the Northeastern states, Kerala and coastal Karnataka while being scattered over south interior Karnataka. Widespread rain or thundershowers is expected to occur over Lakshadweep during this period.