Wednesday's low-pressure area over south-west Bay of Bengal has intensified into a depression, according to special bulletin from the Chennai Regional Meteorological Centre.
The system lay centred 750 km south-east of Nagapattinam.It is likely to intensify further and move in a west north-westerly direction towards east coast of Sri Lanka during the next 24 hours.
The US Navy's Joint Typhoon Warning Centre, too, has put out a weather alert notice in the south-west Bay of Bengal as a prevailing weather system showed prospects of intensification.
STORM NUCLEUS
The JTWC on Thursday located the area of associated convection to 470 km east of Colombo, Sri Lanka. Animated visible satellite imagery shows sustained and deepening convection beginning to wrap into and organise around a consolidating low level circulation centre (LLCC, the storm nucleus).
Satellites imagery also picked weak winds at the core of a distinct circulation centre with stronger (27 to 46 km/hr) flow located approximately one degree to the north and south of the LLCC.
The upper level environment is conducive for further development with low vertical wind shear (high shear denoted raised wind speeds with height that kills storms) and enhanced outflow, allowing the system to breathe free and grow.
Given this context, the JTWC has upgraded to ‘fair' the potential for the development of a significant tropical cyclone within the next 24 hours (ranging from a depression and above).
Meanwhile, the Noida-based National Centre for Medium Range Weather Forecasting (NCMRWF) under the Ministry of Earth Sciences said that the in its bulletin that the ‘low' over southwest Bay of Bengal and neighbourhood is likely to move west north-westw and may become well-marked.
Isolated to scattered rainfall activity has been forecast for extreme south peninsular India during next 2-3 days before intensifying thereafter.
There is also increasing forecast consensus that the depression might come under the influence of the opposing westerly flows from a prevailing western disturbance over northwest India. International models are of the view that the Bay of Bengal weather system would still manage to cross into southeast Tamil Nadu and adjoining north Sri Lanka.
After making landfall in this manner, however, the weakened system could be made to stagnate while continuing to rain it down over south Tamil Nadu and adjoining Kerala.
A leading cyclonic circulation tracking model is the view that the westerlies would take the system to the north-northeast over land, i.e. towards north coastal Tamil Nadu and south coastal Andhra Pradesh triggering moderate to heavy rains along the way, including over Chennai.
One other tracking model disagreed with this outlook putting the system along a west-northwest track that would take it into north Kerala/coastal Karnataka before leading it into the adjoining coastal Arabian Sea.
This model tends to believe that the system would have the wherewithal to fend off the westerlies, which would have started weakening over the northwest around that time.
The International Research Institute (IRI) for Climate and Society has said that ‘unusually heavy rainfall' is indicated for southwest Bay of Bengal and coastal Tamil Nadu during the five days ending December 14.
Almost similar forecast has been put out by the US National Centres for Environmental Prediction (NCEP), which sees the rains getting sprayed along the Tamil Nadu coast and further north to south coastal Andhra Pradesh.
WESTERLY INFLUENCE
The European Centre for Medium-Range Weather Forecasts (ECMWF) sees the system stagnating over southern Tamil Nadu after being acted upon by westerlies and anchoring the rain session over entire southern peninsula.
Meanwhile, the NCMRWF said that the western disturbance would affect western Himalayan region during the next 24 hours. Under its influence, hilly regions of northwest India are likely to have scattered precipitation while adjoining plains would witness isolated light showers.
Night temperatures over northwest India are expected to increase during the period given the presence of cloudiness brought about by the western disturbance. But the mercury could plunge later as colder northwesterlies fill the plains.
Model predictions suggest that another Western Disturbance is likely to affect northwest India from December 16 onwards.
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