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Vinson Kurian

Thiruvananthapuram April 9 A low-pressure area that sprang up around Kanyakumari has brought welcome showers to the sun-scarred landmass in southern Tamil Nadu, Kerala and parts of north coastal Tamil Nadu.

The "low" had initially formed over southwest Bay of Bengal, off the southwest Tamil Nadu coast, signalling the arrival of the pre-monsoon season, according to Mr J.V. Singh of the National Centre for Medium Range Weather Forecasting (NCMRWF).

The prevailing south-easterly winds will ensure that the `low' travels to the west and continue to cause fairly widespread rain/thundershowers over south Tamil Nadu, Kerala and Lakshadweep. The other wet spot in the country is the North-East, where the westerlies (from the western disturbance regime) are active.

An India Meteorological Department forecast said isolated showers were also likely over coastal Andhra Pradesh, south interior Karnataka and the Andaman and Nicobar Islands.

WIND DISCONTINUITY

Establishment of a "wind discontinuity" along a north-south alignment in the peninsula is the first available indication that the pre-monsoon weather may have set in. A "discontinuity" is a comparatively large contrast in meteorological elements over a relatively small distance or period of time.

A wind discontinuity is a break in the pattern of prevailing winds and results from excess heating of the surface. It could evolve progressively as a trough of low pressure. During pre-monsoon weather, easterly winds blowing from the Bay of Bengal can dump moisture into this feature to aid convection and rain.

The April-May interlude is known to feature an evening `low' in the southern peninsula at one end of the wind discontinuity that runs to the north (up to Nagpur in the instant case). The wind discontinuity has relatively moist southeasterlies to its east and drier northerlies/northwesterlies to the west.

Thunderstorms develop along this line of wind discontinuity in the afternoons/evenings. This is a conventional pre-monsoon weather feature, Mr Singh said.

HEAT WAVE TO HOLD

Mr Jim Andrews of AccuWeather.com does not see any meaningful break in early heat wave in the subcontinent for the next week or so, although the heat will wax and wane somewhat in any given spot thanks to localised weather activity.

Mr Andrews has also predicted that the high-pressure area along the international border would reassert itself and deflect the sub-tropical jet stream (carrier of western disturbances into the country) away to the north of the Indian landmass.

This will prepare the ground for further heating, triggering thunderstorms over southern and eastern India through the latter part of this week.

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`Low' off TN coast signals pre-monsoon weather

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