The North-East monsoon arrived with a bang over parts of Tamil Nadu and Kerala, dumping heavy to very rain while light to moderate showers were recorded over Karnataka and Andhra Pradesh.

According to the India Met Department (IMD), stations in Tamil Nadu and Kerala recording heaviest rainfall during the 24 hours ending on Thursday morning (5 cm and above) are: Puzhal-11; Kelambakkam-10; Periyanaickenpalayam, Perundurai and Cuddalore-9 each; Madhavaram and Avinashi-7 each; Peraiyur, Ennore, Taramani, and Red Hills-6 each; Vedaranyam, Satyabhama University, Sivakasi, and Mahabalipuram-5 each (all Tamil Nadu) and Punalur-9; Myladumpara-8; Konni-6; and Thodupuzha-5 (Kerala).

Heavy rains forecast

The Chennai Met Centre said that heavy rain is likely to occur at isolated places over Tamil Nadu, Puducherry, and South Interior Karnataka on Friday and extend to Kerala from Saturday.

The Thiruvananthapuram Met Centre said that heavy rainfall (7-11 cm in 24 hours) is likely to occur at one or two places in Kerala till the morning of November 4 (Sunday).

Earlier, the IMD said that seasonal rains commenced over Coastal Tamil Nadu, Puducherry, South Tamil Nadu, and adjoining areas of South Coastal Andhra Pradesh and South Kerala on Thursday.

Conditions are favourable for the rains to cover the rest of Tamil Nadu, Kerala, South Interior Karnataka and Rayalaseema by Friday. A facilitating trough of low (not amounting to a conventional low-pressure area) lies over the South-West Bay of Bengal and adjoining Sri Lanka. Another trough runs from here to South Interior Karnataka across Interior Tamil Nadu. A cyclonic circulation hovers over South Tamil Nadu.

‘High confidence’

Global weather models have dropped broad hints that the 10-to-15-day delay in the onset of the monsoon (from the usual October 15-20 window) would be adequately made up.

They cited forecasts of passage of a friendly Madden-Julian Oscillation (MJO) wave after it sets off for its voyage across the Indian Ocean during the ongoing week.

The MJO wave travels periodically from the African coast across the Indian Ocean into the Maritime Continent (S-E Asia region) and the West Pacific, and boosts formation of cloudiness and rainfall on the way.

This ‘wet phase’ of the MJO has presided over monsoon onsets, setting up low-pressure areas and depression, which have gone on to become even cyclones under ideal conditions.

The global models are of the view that the incoming wave would get amplified when it enters the Indian Ocean from November 7 to 13.

Based on good model agreement and relatively low spread among ensemble members, confidence is high in a robust MJO propagating across the Indian Ocean early to mid-November.

‘Low’/depression

And, these models observe that this journey would not be without its attendant benefits for rain-starved parts of the South Peninsula in Tamil Nadu, Kerala and Karnataka.

The Global Forecast System model of the US Climate Prediction Centre sees an elevated chance of a ‘low’/depression developing in the eastern half of the Indian Ocean during the first week.

Confidence is relatively high that a system will develop to the South-East of Sri Lanka. According to a weather tracker of the US National Weather Services, this will move towards the Tamil Nadu coast. It could bring under its rainy spell the entire Tamil Nadu coast and adjoining South Andhra Pradesh, cross the South Peninsula into Kerala, and step out into the South-East Arabian Sea.

Here, it is forecast to gain further traction and redevelop using the warmth of the sea waters, though models do not agree on a single track for its onward movement.

Scarcely would the system have faded out over the Arabian Sea than a fresh system develops over the South-East Bay of Bengal and travels towards the Sri Lanka and South Tamil Nadu coast.

This time, too, Chennai and its neighbourhood could be the likely area of landfall, before setting up ripples in the Arabian Sea just as its predecessor, and move to the East away from the Kerala coast.

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