India Meteorological Department ((MD) has confirmed an outlook being shared by global models of an increase in rainfall activity over the Tamil Nadu coast in the next 4-5 days. Fairly widespread to widespread light to moderate rainfall with isolated heavy falls is being forecast over Kerala and Tamil Nadu during this period.

Fairly widespread to widespread light to moderate rainfall is forecast over the South Peninsula with isolated heavy falls likely over South Coastal Andhra Pradesh and North Tamil Nadu from November 26 to 28.

Scattered light to moderate rainfall is also predicted over the Andaman & Nicobar Islands and Lakshadweep area in what typically is a progression of a sustained wave of rain along almost a straight line over the seas and the islands on both sides of the South Peninsula but mostly confined to the states of Tamil Nadu and Kerala over the mainland.

Easterly wave at work

This is the handiwork of easterly waves which frequent the Bay of Bengal during the North-East monsoon. An easterly wave is a migratory wave-like disturbance within the broad easterly current and moves from East to West (as different from a western disturbance in the North of India from West to East), generally more slowly than the current in which it is embedded.

Although best described in terms of its wave-like characteristics in the wind field, the latest one consists of a cyclonic circulation, as pointed out by IMD on Sunday evening. In the past, easterly waves have hit the waters one after the other, and some have gone on to set up low-pressure areas, depressions or even cyclones in the South Bay of Bengal over which they drift through.

Potent rain-head upfront

They carry a ‘rain-head' upfront that erupts over the Sri Lankan coast or adjoining Tamil Nadu coast but extend rains into Kerala, the Lakshadweep Islands and the adjoining Arabian Sea. Given this, the incoming wave will trigger a fresh wet spell over the South Peninsula, some parts still reeling from the heavy rain brought inland by a depression in the Bay.

The 24 hours ending Sunday morning saw heavy to very heavy rainfall over parts of Konkan and Goa and heavy rainfall at isolated places over Coastal Andhra Pradesh, Rayalaseema, Telangana, Karnataka, Tamil Nadu, Puducherry and Kerala.

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