Sanjeev Kumar Patro

Bhubaneswar: When 'corona warriors' in the country are keenly guarding against the COVID onslaught on the country, the 'cyclone watchers' are keeping a close tab on the Low Pressure Area (LOPAR) formed over Andaman seas. More worrying is another circulation is being observed over Sri Lanka. ECMRWF model shows Kerala on radar.

What makes the job of weathermen onerous this time is, the LOPAR system over Andaman seas has simply kept all guessing. Dissipation signs of LOPAR are few, but the needle tilts heavily towards intensification of the system at a later date.

As per latest release by Regional Specialised Meteorological Centre (RSMC), Delhi, the LOPAR over south Andaman sea and adjoining southeast Bay of Bengal (BOB) persists over the same region. The release added that it is very likely to persist meandering over south Andaman sea and adjoining southeast BoB during the next 5 days (May 9-10).

[caption id="attachment_449321" align="aligncenter" width="650"]Cyclone Amphan image Big Alert: As per ECMRWF, the zone over S Lanka will develop into a TC posing a threat to Kerala[/caption]

A look at the satellite images show presence of cloud clusters over the south Andaman sea. They also indicate a closer circulation of clouds (See the image above).

But the major fact is all closely situated circular cloud clusters never grow up to become a tropical cyclone. History of cyclone genesis over the years across the world has documented that only 8 per cent of closely circulated cloud clusters had evolved into a tropical cyclone.

Will this LOPAR develop to cyclone Amphan?

The south Asian region's ace tropical cyclone watch body, RSMC, Delhi, says intensification of the LOPAR over south Andaman sea and adjoining south east BoB is likely to be a gradual process.

Why RSMC Delhi Thinks So?

As per RSMC, till May 11, there is little probability of increase in convective activity in BoB. The reason: Madden Julian Oscillation (MJO) will move to phase 8 during the subsequent 4 days. It is this weather phenomenon that will keep the LOPAR meandering.

Intensification Factors Strong?

While the sea surface temperature over the entire BoB is over 28 degree Celsius, the south Andaman seas have a SST of around 31 deg C. (see the image below)

sea surface temperature in BoB

Since SST is described as the skin temperature of the seas, wind flow may frustrate this favourable condition.

However, an ECG of the BoB shows prevalence of host of favourable parameters.  The estimated Tropical Cyclone Heat Potential (TCHP) of BoB is very high. The TCHP is estimated at more than 100 kilojoules/cm2 over Andaman sea and major parts of the south and central BoB. (See the image below).

Cyclone Amphan Heat potential

The high value favours the intensification of LOPAR into a tropical cyclone.

Other favourable observations are: Vorticity of air at the higher and lower level, and extension of the system up to upper tropospheric level.

"Lower level positive vorticity observed over parts of south BoB and adjoining equatorial Indian ocean. Small zones of higher positive vorticity measured over south Andaman sea. And the zone over south Andaman sea is extending upto 500 hPa (hecta pascal). But a zone over Sri Lanka is extending upto 200hPa ," informed the RSMC release.

The significant observation is, when the zone over south Andaman is extending through most of the troposphere, the zone over Sri Lanka is extending up to whole of the troposphere.

As per ECMRWF, the zone over Sri Lanka will develop into a cyclone and will moves towards Kerala coast. (see the main image above)

This vertical extension and positive vorticity are the signs that show the zones may develop into a tropical cyclone in coming days.

Landfall When?

IMD-GFS reveals incursion of warm air from equatorial region. The wind in the zone over south Andaman sea is measured at over 10 m/s. Therefore, it predicts formation of cyclone by this weekend. IMD is yet open its card on landfall.

And, ECMRWF (European Centre for Medium Range Weather Forecast) predicts the landfall date will be around May 15-16 and place will be Myanmar.

Almost, all Met models are unanimous that the developing Cyclone Amphan will drift away from Odisha coast towards Myanmar. (see the main image above).