The Hindu Business Line : Deep easterly trough may find match

Thiruvananthapuram, March 25 A deep trough embedded in incoming easterlies may be threatening to empty its contents over the south-east coast in two days from now, but could easily find a match in a counterpart system riding the westerlies from across the northwest border.

The westerlies could offer resistance in the form of an area of ‘wind discontinuity’ (a trough line, almost) running down the west and southwest Bay of Bengal. A ‘discontinuity’ is a comparatively large contrast in meteorological elements over a relatively small distance or period of time.

BREAK IN PATTERN

A wind discontinuity is a break in the pattern of prevailing winds. It could at times go on to become a trough of low pressure. During pre-monsoon weather, easterly winds blowing from the Bay of Bengal dump moisture into this feature to aid convection and rain.

But the easterly wave gets ‘watered down’ after being impacted by opposing westerlies, and generates lesser amount of rain than would be the case had westerlies not come in the way. Still, Tamil Nadu and Kerala are forecast to receive showers Thursday onwards.

Meanwhile, the westerly trough is seen as spinning off an induced cyclonic circulation to spearhead rainfall in northwest India. The westerlies are forecast to dip as far to south as east-central Arabian Sea where the surface temperatures are just right to crank up needed moisture.

HEAVY FALLS

An update by the Regional Met Centre in Chennai said the 24 hours ending Tuesday morning saw rainfall being reported from most places over coastal and north interior Karnataka; at many places over coastal Andhra Pradesh, Rayalaseema and south interior Karnataka.

Very heavy to heavy rainfall were reported (in cm) from Kudathini (Bellary)-14; Kaikalur (Krishna)-12; Yerragondapalem (Prakasam)-11; Jagalpet (Uttara Kannada) and Koppal-9 each; Gadag and Belthangadi (Dakshina Kannada) 8 each; and Kalghatgi and Navalgund (both Dharwad) and Puttur (Chittoor)-7 each.

SYSTEMS WEAKENING

The causative cyclonic circulations were traced to over east-central Arabian Sea off Karnataka-Goa coasts and Telangana, which has since become less marked. The parent ‘low’ over southeast Arabian Sea and adjoining Lakshadweep area, too, had wound down to being a cyclonic circulation.

Forecast for the next two days said that rain or thundershowers are likely over many places in Karnataka and Andhra Pradesh; and at a few places over north Tamil Nadu, Puducherry and north Kerala. Isolated rain or thundershowers are likely over south Tamil Nadu, south Kerala and Lakshadweep.

Meanwhile, in the east, a trough running down from sub-Himalayan West Bengal and Sikkim to North Bay of Bengal through Gangetic West Bengal persisted and is presiding over a wet session in the North-East.

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