The State receives approximately 40 cm of rain during the season that often merges into the pre-monsoon showers.

Vinson Kurian

Thiruvananthapuram, March 6

CONVECTIVE rain or summer showers have announced their arrival to more or less clockwork precision with many parts in the State, especially the South, recording moderate to heavy rain during the three days ending Saturday.

The capital city went through alternate spells of showers and bright sun, a distinctive feature associated with the season, on Sunday. According to Mr M.D. Ramachandran, Director, Met Office, Thiruvananthapuram, the rain activity has commenced at least a week in advance of what has traditionally been considered the normal.

The State receives approximately 40 cm of rain during the season that often merges into the pre-monsoon showers in due course. It had a bountiful summer shower season in the previous year that also saw the southwest monsoon break at least 10 days ahead of normal.

But that was purely coincidental, and there is nothing to suggest a one-to-one correlation ensuring success of the seasons that follow one after the other.

By their very definition, summer rains are purely localised phenomenon resulting from the convection of moisture into the air that rises from an overheated land.

Heating of the land till well past the noon hours would cause the moisture-laden air to rise vertically into the atmosphere and form what are called the convective-type clouds. These cloud formations can rise to as high as 10 km straight up.

Due to the nil or negligible wind activity during this season, these formations would not move from their resting place. Once sufficiently cooled, the formation gives itself away in the form of showers with associated thunder activity.

It tends to occur in the latter part of the day or early evening. Because land warms faster than the sea, this type of rain is far more common over land.

Even sudden and sustained outbursts, called cloudbursts, are commonplace during this season with showers giving way to heavy downpour, running up to seven to eight cm in measure and confined to a given area.

A chain of such thundercloud formations, or `cells' in Met jargon, can link practically the length of the State during this season. This goes to explain the often `wide-spread' nature of these `localised' rains.

The district-level forecasts by the National Centre for Medium Range Weather Forecasting (NCMRWF) also indicate that the State will continue to experience showers of varied duration during the days ahead.

The Centre had rightly forecast a peak in rain activity on Saturday (March 5). The next peak has been forecast for March 8 (Tuesday) in the latest five-day forecast.

The Weather Watch report dated March 3 issued by the Department of Agriculture and Cooperation said the all-India cumulative seasonal rainfall recorded from January 1 till February 24 was above normal by 81 per cent.

In the southern peninsula, it was in excess by 25 per cent. The northwest region has run up a huge 111 per cent surplus during the ongoing season.

(This article was published in the Business Line print edition dated March 7, 2005)
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