The Hindu Business Line : Cross equatorial flow picks up; to aid monsoon currents

THE India Meteorological Department (IMD) has said that the build-up to the southwest monsoon has received a further boost with the cross equatorial flow picking up in strength.

"I feel things are brightening up. The cross equatorial flow has strengthened," said Dr M. Rajeevan, Director, Forecasting, IMD, Pune. This flow has much significance attached to it in so far as it is the principal driving force that guides the moisture-carrying winds originating from Southern Indian Ocean towards peninsular India.

Another useful synoptic condition helping the overall scheme of things is the formation of a wind shear zone from West Central Bay of Bengal to Southeast Arabian Sea with embedded cyclonic circulations. On Tuesday, one such circulation lay over the West Central Bay, off the Andhra coast, and the other, over Tamil Nadu and adjoining Kerala.

Wind shear is defined as the amount of change in the wind's direction or speed with increasing altitude. The vertical wind shear in a tropical cyclone's environment is vital for its further evolvement.

When the wind shear is weak, the storms that are part of the cyclone grow vertically, and the latent heat from condensation is released into the air directly above the storm, aiding in development. When there is stronger wind shear, this means that the storms become more slanted and the latent heat release is dispersed over a much larger area.

The wind shear has the ability to pull in the monsoon currents, Dr Rajeevan said. If it persists, it should aid further advance of monsoon. As for location coordinates, he said he wished if the zone lay along an east-west trough, rather than north to south, as it did on Tuesday. The east-west alignment would have been ideal, viewed from the monsoon angle. In its weather update, the IMD said on Tuesday that the southwest monsoon further advanced into parts of East Central Bay of Bengal and further into South Bay of Bengal. Conditions are favourable for its advance over parts of the Northeast Bay and the Central and South Bay during the next 48 hours ending Thursday morning.

Rain/thundershowers have been forecast at many places over the Andaman and Nicobar Islands, Coastal and South Interior Karnataka, Kerala and Lakshadweep and at a few places in the rest of the southern peninsula. A warning on the likely prospect of isolated heavy rainfall over Andaman and Nicobar, Coastal Karnataka, Kerala and Lakshadweep has also been issued.

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