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Sanjeev Kumar Patro

Bhubaneswar: With the Madden Julian Oscillation (MJO) going to turn favourable during the period of May 14 -18, the weathermen are seemingly on the tenterhooks over the persisting cyclonic circulation over south Andaman sea and adjoining Sumatra coast. They have assigned the area the status of 'invest' - means on watch list.

The big development today is the system is extending up to the mid-tropospheric levels, and also the formation of a Low Pressure Area (LOPAR) again on around May 13 (Thursday).

Since April last, meteorologists were quite anxious over the evolution of this cyclonic system over the south Andaman sea to a tropical cyclone. Even, 'Amphan' name was suggested by Thailand. The system was predicted to acquire a very severe cyclonic storm stature in the first week of May, before making landfall in Myanmar on May 3.

The likely birth of cyclone Amphan in Bay of Bengal had even popped  up the old memories of another very severe cyclonic storm Fani that pummelled Odisha last year on May 3 in a big way.

Why Cyclone Amphan's birth delayed?

It's the Madden Julian Oscillation (MJO) that proved a roadblock on the way of cyclone Amphan's birth. MJO was at its peak or say strongest during the birth of Fani; whereas it slipped into weak zone during the birth of cyclone Amphan. It's lack of this 'right timing' that delayed the formation of cyclone Amphan.

While Fani took birth (on April 26) during MJO's enhanced rainfall phase, Amphan's birth was delayed as the same MJO slipped into the phase of suppressed rainfall or say the dry phase. The LOPAR for cyclone Amphan came into existence on around April 30, when the MJO was slipping into the unfavourable zone.

However, the new twist here is MJO will gain the amplitude of more than 1, and also enter the Indian ocean during the period of May 14-18. The activated state of MJO will give a boost to cyclone genesis, given that the cyclonic circulation is still lying over the south Andaman sea and the adjoining Sumatra coast.

Will Amphan become a reality now?

As per IMD, the cyclonic circulation over south Andaman sea and adjoining Sumatra coast is likely to move northwest wards gradually and under its influence a Low Pressure Area (LOPAR) is likely to form over south-east Bay of Bengal and adjoining Andaman sea around May 13.

As per Meteologix data, the cloud top temperature of the system has increased and is measured in the range of (-) 66 degree Celsius to (-) 83 deg C. (See the image below).

But the hurdle in its faster development is significant decrease in warm moist air around the 'invest' area. Therefore, IMD says no cyclone genesis till May 14. Coincidentally, MJO is also in weak phase till May 13.

Besides, factors like upper and lower level vorticity, lower convergence and upper divergence zones have also decreased or say have turned unfavourable.

What Models Say?

ECMWF: The most accurate model of world indicates cyclonegenesis over southwest Bay of Bengal around May 16, and intensification of it into a cyclonic storm stage with near west-northwest ward movement over south west BoB. It's showing around 30 per cent probability of the storm moving towards Tamil Nadu coast vis-a-vis 20 per cent for Myanmar. (see the image below)

INCOIS: Government of India's premier ocean research agency wind model shows the LOPAR is going to form near Tamil Nadu coast, though it is yet to forecast its likely track. INCOIS analysis also shows high Tropical Cyclone Heat potential(TCPH) in the same area.  (see the images below).

IMD-GFS and NCUM predict cyclonegenesis over southeast BoB around May 15 with near northeast ward movement and intensification upto severe category cyclone. NCUM models show steep fall in pressure of the system to indicate its severe category. (See the images below).

Any Impact On Odisha: The latest ECWMF storm tracking holds a threat to Odisha. The storm track probability towards Odisha is around 15-20 per cent. In NCUM model, some impact over Odisha is also shown, despite the system hitting the north Myanmar coasts (see the images above) 

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