True to forecasts, a depression formed over Gulf of Aden (South-West Arabian Sea) last evening and lay centred 540 km East-North-East of Aden (Yemen) and 420 km West-North-West of Socotra Islands.

India Met Department (IMD) put it under watch for further intensification as a deep depression later today, and a movement towards the Yemen coast and then into its hinterland.

Squally winds seen

Squally winds reaching 45-55 km/hr in speed and gusting to 65 km/hr are likely around the centre of the system covering Gulf of Aden and the adjoining areas of West-Central and South-West Arabian Sea.

Sea condition will be rough to very rough and IMD has warned fishermen against venturing into Gulf of Aden and adjoining areas during the next two days.

Nearer home, the persisting cyclonic circulation over the Comorin-Maldives area continues to engage the attention of forecasters for signs of further development.

The European Centre for Medium-Range Weather Forecasts and the ensemble model of the US National Centres for Climate Prediction (NCEP) are assertive about this outlook.

They however differ in the track of onward movement of the system, with implications for the West Coast of India (Kerala-Karnataka-Goa), Lakshadweep Islands and the Maldives.

Buzz off Kerala

Monsoon forecasters are eager to see if this system could actually precipitate seasonal rains along the Kerala coast in another seven to 10 days when the track will become known.

For starters, the European Centre sees wind speeds around the cyclonic circulation starting to build around the South Kerala coast from this weekend (May 20 onwards).

It sees the system intensifying into a low-pressure area close to the North Kerala-Karnataka coast, and further intensifying into a depression or even a cyclone off Kerala-Karnataka coast by May 26.

But it would not cross the coast, but be scooped up by passing western disturbance dipping deep into South-East Arabian Sea, and pulled up North along the Kerala-Karnataka coast.

It would then be guided away by the disturbance to the outer seas of East-Central Arabian Sea, giving it ample room for further intensification.

US model differs

If this were to pan out, the south-westerly winds commandeered by the system would most likely precipitate the onset of the monsoon along the way.

But the US NCEP plots a differently track for the system, taking it progressively away from the Comorin-Maldives and straight to the West, along the same track as the deep depression before it.

It would intensify into a cyclone by the time it barrels into the Gulf of Aden or South Yemen, the second successive time for the coast on the Arabian Gulf. The IMD too is in agreement with this, for now.

Interestingly, the US agency goes on to suggest that the Madden-Julian Oscillation (MJO) that is firing up the Arabian Sea, would not have been spent out with even this.

The South-East Arabian Sea off Kerala might erupt for a third successive time, sending off another system along a familiar West-North-West track away to the Oman coast.

Simultaneously, the Bay of Bengal on the other side would be put into a tizzy, with a low-pressure area likely springing up over the Andaman & Nicobar Islands.

Churn in Bay?

This is forecast to intensify and move in a West-North-West track towards the Andhra Pradesh coast, likely keeping the monsoon in good stead.

In a scenario where the leading Arabian system moves away and takes the monsoon winds with it, the Bay system should help by sustaining the Bay arm of the monsoon and directing rains inland.

The churn in the Arabian Sea followed by that in the Bay of Bengal would be in keeping with the West to East movement of the MJO wave which packs convection, clouds and heavy rain.

The arrival of the wave from West Africa is often tracked to decide the onset of the monsoon over India, not to mention formation of low-pressure areas, depressions or even cyclones.

Both the seas are literally on the boil with warm sea-surface temperatures of around 30 deg Celsius, which helps with convection and the process of cloud building.

The MJO wave also has a 'dry phase' when it rings in the 'break-monsoon' after the onset phase, leading to a sustained lull in rain activity over mainland India.

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