The Hindu Business Line : Easterlies drive rain in South

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Thiruvananthapuram Feb. 19 Easterly winds packing a smattering of moisture have been causing scattered rainfall in extreme southern peninsula over the past few days.

Convective activity may also have contributed to the denouement with some places in southern Tamil Nadu, as well as adjoining Kerala receiving isolated heavy falls on Sunday.

When air is heated from below, it expands and rises; as it cools down with height, condensation occurs to form cumulonimbus clouds from which heavy rainfall is produced. But the wet session will not last long, according to Mr J. V. Singh of the National Centre for Medium range Weather Forecasting (NCMRWF).

Weather system

On Monday, satellite pictures showed cloud cover over Southeast Arabian Sea, off and along the Kerala/Konkan coast. But, there is nothing to suggest some kind of a weather system — rare at this time of the year — that could sustain the precipitation.

The Inter Tropical Convergence Zone (ITCZ), the seasonally migrating band of `low' that causes weather systems (low pressure, depression) to form, is still located far to the south of the mainland and cannot be expected to influence local weather just yet.

The ITCZ will meander in tandem with the Sun's movement across the Equator into the northern hemisphere and will locate itself to within and around peninsular India to trigger the southwest monsoon during May/June.

Meanwhile, in the North, an incoming feeble western disturbance (WD) is expected to affect the western Himalayan region on Wednesday.

Temperatures may drop during the intervening period, but will pick up coinciding with the arrival phase of the WD.

But a follow-up WD forecast to cross in by the weekend would most likely feature an induced cyclonic circulation, the type of which had triggered the first substantive rain activity of the winter, critical to rabi crop prospects, from February 9 to 11.

But forecasters have not been able to assess the magnitude — or spread — of the incoming WD that has crucial ramifications for its `productivity'. The preceding `biggie' system had a reach extending south to Gwalior in North Madhya Pradesh. This ensured that even parts of the peninsula, Rayalaseema, for instance, were brought under its footprint.

The resultant rainfall, at times heavy and widespread, held forth for almost a week and was above normal for this time of the year at a number of places. This brought about a reversal in cumulative rainfall for the season starting, with the deficit being brought down to 27 per cent as on February 14 (against 83 per cent at the end of the preceding week).

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