The Hindu Business Line : Cyclonic circulation drifts away

The cyclonic circulation in the south-east Arabian Sea has drifted in a west-northwest direction, away from the peninsular coast, even as easterlies over the Bay of Bengal shifted into lower gear.

The Arabian Sea system was itself part of the larger easterly wind regime, and there was little chance it would have moved north-northeast towards the peninsular coast, said Dr Akhilesh Gupta.

Set to weaken

In the instant case, the easterly wave packed the convection zone upfront, which dictated the direction in which it would move laterally. It is predicted to weaken with the west-northwest movement, given the unfavourable wind shear and lack of `ventilation' at the top.

The Bay of Bengal is now clear of cloudiness, and is likely to witness reduced turbulence for some days from now. Adjoining South China Sea and the western Pacific are also calm and house no significant weather system.

According to Mr Gupta, it is unusual that no named cyclone has formed in the Bay even as the season has advanced into the latter part of November. He attributed this to the absence of migrating systems from the eastern oceans and flawed positioning of the Inter Tropical Convergence Zone (ITCZ).

A band of `low' encircling the globe, the ITCZ is still currently drawn to a position much south than the usual. It was more or less aligned with the Equator, where it is least productive in terms of generating turbulence and rainfall.

The ITCZ has to move north to within a band of 5 deg N to 10 deg N longitudes to spin off independent systems that could develop into low's and depressions. But it was not likely anytime soon that the ITCZ would move sufficiently north to make this happen.

Mr Tony Barnston of the International Research Institute for Climate and Society of Columbia University had earlier observed that the creeping El Nino would cause the southern reaches of the Bay to warm sufficiently to help throw up weather systems.

But, according to Dr Gupta, warm seas do not create systems unless the atmosphere plays ball. And systems forming during December are not normally known to live their full life, often dissipating over the seas or straying in the open waters.

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