An expected second low-pressure area forming over the South-East Bay of Bengal and South Andaman Sea by Wednesday is expected to move West-North-West and intensify as a depression over the central parts of the South Bay by Friday, India Meteorological Department (IMD) has said. Earlier, the first ‘low’ in the Bay had become ‘well-marked’ as it approached the Tamil Nadu coast, and dumped heavy to very rain and even extremely heavy rain in some parts of the state during the last couple of days. After weakening, it crossed into Kerala and entered the Arabian Sea where it weakened further and dissipated. 

Weather watch by Vinson Kurian

Cyclonic circulation forms

The IMD said on Tuesday, a preparatory cyclonic circulation hung over the South Andaman Sea, which would descend to lower levels in the atmosphere to become a fresh ‘low’ and intensify as a depression. It would bring back widespread rainfall to the Andaman and Nicobar Islands, the first land feature of impact, accompanied with heavy rain isolated places on both Wednesday and Thursday. Squally weather with winds speeding to 40-45 kmph gusting to 55 kmph will prevail over the South Andaman Sea and adjoining South-East Bay on Thursday; over the South-East Bay on Friday and Saturday; and over the South-West Bay and adjoining Sri Lanka, not far way from the South Tamil Nadu coast, on Friday and Saturday, the IMD said. 

Numerical weather forecast

Guidance by the IMD’s numerical models suggest that the system may intensify by another round, if not more, before it reaches the Tamil Nadu coast by the first half of the next week (around November 22). It may plough through the interior and reach the Kerala and Karnataka coasts by when the next low-pressure would likely have been initiated from the South-East Bay of Bengal. This is, however, subject to validation on the ground. The IMD warned fishermen against venturing into the South Andaman Sea and adjoining South-East Bay on Wednesday and Thursday; the South-East Bay on Friday and Saturday; the South-West Bay and adjoining Sri Lanka coast on Friday and Saturday; and along and off the Tamil Nadu-Puducherry coasts on Sunday and Monday. 

Negative IOD dying 

Meanwhile, the Australian Bureau of Meteorology indicated on Tuesday the negative Indian Ocean Dipole (IOD) values may have weakened, and even dissipated. While a rain-driver La Niña is in place over the tropical Pacific, the Bureau suspects that the IOD values may return back to neutral soon. During the 24 hours ending on Tuesday morning, a number of places in Kerala and Tamil Nadu received moderate to very heavy rain from a remnant cyclonic circulation from the first ‘low’) over South-East Arabian Sea and a trough that linked it with the Comorin area via South Tamil Nadu.

The chief amounts of rainfall (in cm) generated in this manner (above five cm) are:Tamilnadu: Nalukukku-12; Mahabalipuram and Kakkachi-9 each; Lower Kothaiyar and Kulasekarapattinam -7 each; Thirukalukundram and Perambur-6 each; Ayanavaram Taluk Office,Tindivanam, Mylaudy and Kottaram-5 each. Kerala: Konni-11; Kochi Airport, Mancompu, Kakkayam and Konni ARG-7 each; Alappuzha, Kollam, Kanjirappally, Nilambur and Muvattupuzha-6 each;Kottayam, Mavelikkara, Perumbavur, Seethathode and Vynthala- 5 each. 

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