The Hindu Business Line : `Heat low' builds to drive monsoon into north

Thiruvananthapuram June 12 Excessive heating of the north and northwest has provided the perfect backdrop for the all-important `heat low' to build in the northwestern sector and adjoining Pakistan, which is a good augury for the progress of southwest monsoon.

The `heat low' helps throw in the required atmospheric pressure values and aligns it along a suitable gradient from the south (Thiruvananthapuram with atmospheric pressure of around 1010 millibars) to the northwest (west Rajasthan, at 992 millibars) along which the monsoon sprints to upcountry destinations.

OPPRESSIVE HEAT

The sun-scalded Sri Ganganagar in Rajasthan recorded 48 degree Celsius on Monday, while across the border in Pakistan, the situation was much worse with mercury shooting past the 50 deg C-mark at a few places. But some respite from the sweltering conditions has since come about with the incursion of cooler easterlies in the northwest.

According to Mr Jim Andrews of AccuWeather.com, the surface wind flow over the peninsula is more or less as it should be now with plenty of gale-force west to southwest winds north of the Indian Ocean Equator. South-East trade winds are re-curving smartly east of Africa to transform themselves as monsoon southwesterlies.

A high-pressure area holds sway over Arabia and Iran to northwest India whereas a deep heat low (which anchors the monsoon trough) has been set up over Pakistan, Mr Andrews said.

PERFECT SETTING

A perfect setting has been made for a strong monsoon pulse to reach the southwest coast over the next three days, said Dr K. J. Ramesh of the Department of Science and Technology. Projections by the European Centre for Medium-Range Weather Forecasts (ECMWF) indicate that the monsoon is engaging itself into top gear by the weekend.

The strong flows will continue through the weekend and into the next, and could even induce the formation of two middle-level circulations on either side of the peninsula - one over the Arabian Sea and the other over the Bay of Bengal - according to ECMWF projections.

According to Dr Ramesh, this would represent the most active phase of monsoon scripted on the broad canvas of an east-to-west `shear zone' of monsoon turbulence (featuring strong easterlies in the upper layers of the atmosphere and southwesterlies in the lower levels).

The `easterly jet', another major monsoon component, would have become established by then along the southern latitudes.

A western disturbance predicted to roll into the northwest around this weekend and bound to travel to the east may actually help perk up the rainfall activity as it expectedly interacts with prevailing easterlies in the north. Further progress of monsoon may get held up for sometime, but the confluence could produce good rainfall over the hills and parts of the plains.

An update by the India Meteorological Department said conditions continued to remain favourable for further advance of monsoon into parts of Konkan, Goa and south madhya Maharashtra and some more parts of interior peninsula and east India during the next four days.

Numerical model predictions indicate an increase of ongoing rainfall activity along the west coast and east India during the next three days. Isolated heavy to very heavy rainfall is likely over the northeastern States, West Bengal, Sikkim, south Konkan, Goa, coastal Karnataka, Kerala and Lakshadweep.

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