Conditions are becoming favourable for advance of the South-West monsoon over the South Andaman Sea and Nicobar Islands by May 15, five days ahead of the normal date.

The India Met Department (IMD) made this assessment on Wednesday based on ‘forecast synoptic conditions from dynamic models and prevailing large-scale features’ ruling over the region.

The advance of the monsoon over the Andaman Sea normally takes place around May 20 with a standard deviation of about a week. This means that the event will take place in “the upper-most band of a week-long window”.

But this has to be verified in the next few days with enhanced convection (cloud-building) and increased rainfall activity over the Bay of Bengal and the Andaman Sea.

Past data rule out any one-to-one association of the date of the monsoon advance over the Andaman Sea with the date of the monsoon onset over Kerala or with seasonal monsoon rainfall over the country.

Classical features present

Meanwhile, KJ Ramesh, Director-General, IMD, told BusinessLine that the physical setting, evolution and progress of the monsoon along the fringes of the Arabian Sea and the Bay of Bengal “align with their known classical features”.

The cross-equatorial flows that bring the monsoon from the southern hemisphere are currently strong. The process of convection, too, has been on course with a strong band of cloud showing up across the Equator for a third day.

“The fact that this (presence of the cloud band) has proved much more than being a one-day wonder points to what is probably brewing in the background,” Ramesh said.

Added to this is the sustained heat wave over North-West India, which helps the monsoon’s cause by setting up a suitable pressure/temperature gradient for the moisture-laden winds to blow in from the Kerala coast into the North.

Rainfall quantum

Meanwhile, the IMD has not calculated the quantum of expected rainfall from the season this year except that “it is going to be higher than what was forecast (96 per cent with an error of +/-5 per cent)” in its first long-range forecast in April.

This is based on the latest update from the Australian Bureau of Meteorology, stating that prospects of a strong El Nino developing in the Equatorial Pacific have receded.

The El Nino phenomenon has often had a drag effect on the monsoon.

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