Weather forecast. ‘Low’ in Bay turns well-marked, on course to become cyclone tomorrow

The low-pressure area over South-East Bay of Bengal and adjoining South Andaman Sea became ‘well-marked’ on Tuesday over the South-East Bay in the first round of an expected series of intensification. India Meteorological Department (IMD) said on Tuesday it will undergo two more rounds of intensification and be declared as a cyclone, named ‘Mandous’, by Wednesday evening.

By Thursday morning, ‘Mandous’ would have entered the South-West Bay near North Tamil Nadu, Puducherry and adjoining South Andhra Pradesh coasts. The IMD’s projections said the cyclone would likely strike a pause off the coast for the next two days without intensification or weakening, and suggested that it may cross coast by Friday evening or early Saturday morning.

Rains to escalate over TN

The IMD said rainfall will escalate at a few places over North Coastal Tamil Nadu, Puducherry and Karaikal, with isolated heavy rainfall from midnight of Wednesday. Rains may further increase, covering most places, and with heavy to very heavy rainfall and extremely heavy falls at isolated places from Thursday as the cyclone nears the coast. It will be isolated heavy to very heavy over Tamil Nadu on Friday and over interior Tamil Nadu on Saturday. 

As for adjoining South Coastal Andhra Pradesh, the rains will scale up to being enhanced at a few places, turning into isolated heavy rainfall from midnight of Wednesday. It is likely to increase, with rainfall at most places and isolated heavy to very heavy rainfall on Thursday, and isolated heavy rainfall on both Friday and Saturday. 

‘Benign’ western disturbances

A cursory glance towards the north of the country indicates a passing western disturbance, which has often interfered with the track of the incoming low-pressure system in the Bay, having entered North Rajasthan. A fresh feeble disturbance may affect the hills of North-West India from Wednesday night. Neither will wield the strength to unsettle the cyclone, early forecasts suggest. 

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Short-tomedium-range predictions by IMD’s numerical models indicate the cyclone may hit the home stretch towards Chennai on Saturday, pausing off the coast on Friday and weakening in the process. After landfall around Chennai, it is predicted to move inland and enter the South-East Arabian Sea off Kerala-Karnataka, where it is likely to re-energise itself. 

Flare-up to follow?

The model runs indicate a flare-up along the Chennai region almost a week after (around December 15), possibly by remnant flows of the cyclone. This is seconded by the US National Centres for Environmental Prediction, which signals the probability of a phase of enhanced rainfall for the Tamil Nadu coast, though focused more to the South and adjoining Sri Lanka, from December 13 to 21.

The Chennai Met Centre has forecast light to moderate at many places on Wednesday with thunderstorms and lightning, before blowing up as heavy rain over Cuddalore, Mayiladuthurai, Thanjavur, Tiruvarur, Nagapattinam and Pudukkottai districts. This is of a piece with Monday, which saw an active phase of a North-East monsoon over South Tamil Nadu conjured up by an easterly wave.

The wave triggered heavy to very heavy rain of 16 cm each over Thanjavur, Nalumukku and Oothu; 15 cm at Kakkachi; 14 cm at Needamangalam; 13 cm at Manjolai; 12 cm at Lower Anaicut; 11 cm each at Nannilam, Valangaiman and Kulasekarapattinam and 10 cm at Tiruvaiyaru. Many other centres recorded moderate to heavy to very rainfall of up to 10 cm the same day. 

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