Other ambient conditions in the Andamans are near consistent with the onset, evidenced best in the persistent cloud cover and the dominant southwesterlies.

Vinson Kurian

Thiruvananthapuram, May 25

THE low pressure system located to the extreme southwest of the peninsula on Tuesday may have faltered, but things are just about falling in place for the onset of the southwest monsoon over the Andamans - the first port of call within the territorial waters - as early as Thursday.

The India Meteorological Department (IMD) could have declared the onset here on Wednesday itself, but for the sudden lull in the prevailing rain activity over this distant outpost in the Southeast Bay of Bengal, said Dr M. Rajeevan, Director-Forecasting. But he expected the declaration to take place on Thursday.

The normal date for onset here is around May 15.

Other ambient conditions in the Andamans are near consistent with the onset, evidenced best in the persistent cloud cover and the dominant southwesterlies. It may be seven to 10 days before the system makes what is being seen as a delayed landfall over the mainland along the southwest coast.

The prevailing heat wave across many States is expected to provide the perfect backdrop for the spectacle to unfold, with the peninsula offering itself as a `trough' (initially categorised by IMD as a `wind discontinuity' extending from Chattisgarh in the north right up to Tamil Nadu) for the southwesterlies to shower their contents.

The perfect formation and deliverance of Tuesday's `low' would have created the ideal pre-monsoon build-up for the onset along the southwest coast. But its fizzle-out only reveals the capricious nature of the tropical weather system, which weathermen have long tried to come to terms with, but not always with success.

Because of the country's inverted triangular shape, the land is heated progressively as the Sun moves northward. This accelerates spread of heating; combined with the general direction of heat being transported by winds, there is greater initial monsoon activity over the Arabian Sea than the Bay of Bengal. The relative humidity of coastal districts rises above 70 per cent.

The onset is recognised as a rapid, substantial and sustained increase in rainfall over a large scale. Typically, the rainfall amount increases from 5 mm to over 15 mm a day in less than five days during onset. But the onset shows little or no association with monsoon strength.

An IMD weather update on Wednesday said heat wave conditions prevailed over most of central and peninsular India.

The trough of low over the South Andaman Sea and the adjoining Southeast Bay of Bengal persisted.

(This article was published in the Business Line print edition dated May 26, 2005)
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