Pacific cyclone and monsoon onset

Pacific cyclone and monsoon onset

India Meteorological Department (IMD) on Monday evening said that scattered rain or thundershowers would unfold over Lakshadweep, coastal Karnataka, Kerala and Andaman and Nicobar Islands until Wednesday and increase thereafter.

An extended outlook valid until Saturday said that the rains would become fairly widespread over extreme south peninsula and Andaman and Nicobar Islands.

This clearly is thought to be a clear indicator of the approaching onset of southwest monsoon, being facilitated by a raging tropical cyclone, Songda, in the northwest Pacific. The cyclone system is part of the larger Asian monsoon system that covers the northwest Pacific, South China Sea, the Bay of Bengal, equatorial Indian Ocean and the Arabian Sea.

Purely coincidental, formation of this cyclone would have some impact on the onset phase of the Indian monsoon, though seen largely beneficial in the preliminary analysis.

Songda is, however, is forecast by most models as intensifying into a super cyclone (of Category-4 strength and above) and racing away to north-northeast off the Philippines towards East China Sea and beyond.

All northwest Pacific cyclone systems tracking in east-northeast direction are considered inimical to the interests of the Indian monsoon since they would also wake away a lot of moisture with them.

The London-based Tropical Storm Risk group said that Songda might reach super cyclone status by Saturday.

This would mean that once the onset of monsoon over India's southwest coast is facilitated, Songda would divert moisture across the Bay of Bengal into Southeast Asia and pull the same towards itself.

In the process, the onset of monsoon over Andaman and Nicobar Islands and Sri Lanka might take place one after the other. The normal timeline for the Andaman Sea onset if May 15 to 20.

Some other models, including Roundy-Albany and the Taiwanese Central Weather Bureau, still see the possibility of a separate system developing in the Arabian Sea and clambering up north towards Mumbai-Gujarat region.

This is expected to happen during the first week of June, these models indicated, after the monsoon has set in over the Kerala coast