North-East monsoon arrives, heavy rain forecast for Tamil Nadu, Kerala, Karnataka

The 2019 North-East monsoon arrived quietly over Tamil Nadu and adjoining Andhra Pradesh, Karnataka and Kerala a day ahead of the forecast date, marked by widespread rainfall over the region.

The 24 hours ending on this Wednesday morning, saw moderate to heavy rain being reported from Hassan (10 cm), Kavali (7 cm), Tirupathi (6 cm), Agumbe, Atiramapattinam and Ongole (5 cm each), Shirali, Mysore and Nellore (4 cm each); and Udhagamandalam (3 cm).

Lacks the usual flourish

The arrival phase may have lacked the usual flourish in the form of a rain-driving low-pressure area, depression or even advance cyclone, but global models indicate that both the Bay of Bengal and the Arabian Sea might catch up sooner than later.

According to the Climate Prediction Centre of the US National Weather Service, the North-East monsoon may entrench during this week and the next, with the week from October 23 to 29, likely witnessing action in both the peninsular seas.

The US agency has indicated the likelihood for two areas of low pressure (one in the Arabian Sea, and the other in the Bay of Bengal) embedded in the broad low-pressure area centered over the Indian subcontinent.

Since early October, a stationary presence of enhanced convection (cloud-building and rainfall) was centered over Africa, according to the US agency, with a suppressed convection over the South China Sea.

Its forecasts also favoured the re-emergence of a rain-boosting Madden-Julian Oscillation (MJO) wave, that periodically passes over the Indian Ocean from Africa to the South China Sea, over the next couple of weeks.

The MJO wave is a band of low pressure encircling the globe and carries clouds and rain, and has been credited with initiation of low-pressure areas, depressions and cyclones, apart from precipitating onset of monsoons along the way. The arrival of the MJO wave and likelihood of its movement of its entourage over the next two weeks lends credence to the possibility of formation low-pressure areas/depressions as has already been forecast.

Pacific developments

In the West Pacific, the US Joint Typhoon Warning Center (JTWC) is monitoring an area of low pressure for signs of further development while tracking West-North-West towards Luzon, Philippines.

Its movement too will be watched for the potential favourable impact on the North-East monsoon over South India, provided it maintains the track, since a remnant could get directed into the Bay of Bengal.

In addition, global models have also have indicated another storm development further east near Micronesia with the potential for rapid intensification.

Back home, the India Met Department (IMD) said that the incumbent South-West monsoon withdrew from the entire country , paving the way for the North-East monsoon to sneak in over Tamil Nadu and adjoining areas of Andhra Pradesh, Karnataka and Kerala.

Presiding over the affairs on the day of the onset was a cyclonic circulation over East-Central Arabian sea off the South Karnataka coast, which most models have put under watch for signs of intensification.

Another helpful atmospheric feature was the trough, an elongated reservoir of moisture being fanned in by winds from the seas on either side of the South Peninsula, and ran up to link with the cyclonic circulation over the Arabian Sea.

"Under the Influence of the above systems, fairly widespread to widespread rainfall with isolated heavy falls is likely the South Peninsula during the next four days," the IMD said. 

An extended outlook from October 21 to 23, said that fairly widespread to widespread rainfall with isolated heavy falls is likely over the South India and Maharashtra.

Scattered to fairly widespread rainfall has been forecast also over East and Central India, sharing the spoils of the onset phase of the 'monsoon in reverse.'

Detailed forecast for Wednesday and Thursday spoke about the possibility of heavy to very heavy rainfall over Tamil Nadu, Puducherry and Kerala; it would be heavy over Coastal and South Interior Karnataka, Lakshadweep, Coastal Andhra Pradesh and Rayalaseema.

Thunderstorm accompanied with lightning has been warned of over Konkan, Goa, Assam, Meghalaya, the North-Eastern States, Tamil Nadu, Puducherry, Kerala, Lakshadweep, Karnataka, Coastal Andhra Pradesh, Rayalaseema and Telangana.

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