India Meteorological Department (IMD) has declared a fresh alert for a depression over the Bay of Bengal in the next three to four days. A preparatory cyclonic circulation will emerge over the South Andaman Sea by Sunday and intensify as a low-pressure area over the South-East Bay and adjoining South Andaman Sea the very next day, the IMD said in its noon update today. 

It expects the system to track to the West-North-West and intensify further as a depression in the next few days (by Wednesday next). The prospective depression, too, will stick to the West-North-West track and near the Tamil Nadu-Puducherry coasts on Thursday, the IMD said, without mentioning the probability of its strengthening further or area of landfall. 

Easterly wave active 

The genesis of storm-like conditions over the Bay will be layered over a concurrent easterly wave that has been bringing isolated to scattered light to moderate rainfall over Karnataka, Kerala, Tamil Nadu and Lakshadweep. This will continue over the next four to five days even as the low-pressure area takes form over the South-East Bay and South Andaman Sea.

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Satellite pictures on Tuesday evening showed big blobs of thunderstorms over South Kerala and adjoining ghat areas of Tamil Nadu. Heavy rain was reported over these parts on Monday.

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Rainfall activity is likely to increase first over gateway Andaman and Nicobar Islands with light to moderate fairly widespread to widespread rainfall and isolated heavy falls from Monday. Short- to medium-term guidance by IMD’s numerical models indicate that the depression (even deep depression) may approach the Puducherry, South Tamil Nadu and Sri Lanka coasts by Thursday. 

 It is forecast to swiftly negotiate South Tamil Nadu and adjoining South Kerala, taking advantage of the lower heights of the ghats in the region, and emerge into the South-East Arabian Sea in the subsequent days (December 10-11). This phase will also likely witness the initiation of a fresh cyclonic circulation off the Sumatra Coast and adjoining South Andaman Sea. 

Make-or-break system?

The US National Centres for Environmental Prediction is of the view that the current week (December 1-8) will see light to scattered moderate rain along the South Andhra Pradesh-Tamil Nadu coast. The rains will escalate to heavy along the North Tamil Nadu and South Andhra Pradesh coast as also adjoining interior, covering Rayalaseema and South Interior Karnataka during the following week as the depression bears down over the Tamil Nadu coast. 

Chennai-based weather bloggers see the incoming depression as a make-or-break weather system for the South Peninsula after the silent period following the passing of a predecessor well-marked low-pressure area (one step lower than depression). It had failed to live up to expectations after spending itself out mostly over the seas, while raining sparingly over land. 

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