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Heavy rain to continue over South India as 'low' bides time

Vinson Kurian Thiruvananthapuram | Updated on October 20, 2019 Published on October 20, 2019

Detailed IMD forecast for Sunday said that heavy to very heavy rainfall lash isolated places in South India. File Photo   -  The Hindu

The India Met Department (IMD) has extended its outlook, for Sunday, to intensification of a low-pressure area in the Arabian Sea, the fulcrum of the currently enhanced North-East monsoon activity.

Read the IMD weather bulletin here

The 'low' lies over East-Central Arabian Sea (to the North of Lakshadweep Islands and a little distance away from the Karnataka-Goa coasts), topped off by an associated cyclonic circulation.

JTWC Outlook

The US Joint Typhoon Warning Centre (JTWC) has looked at the system (denoted as '97A' with a bearing from the Masirah Island (off Oman) at a distance of 1,230 km to the South-East.

 

 

It has assessed it as 'a broad area of dis-organised convection' (the process of cloud-building that is essential to strengthening as a storm) and minimal upper level turning.

Satellite images further depict small pockets of weak, convective bands to the South and East of the system, essentially referring to the flows from the Arabian Sea and feed-ins from the Bay of Bengal. But low vertical wind shear values (the rate at which winds change direction and speed with height) and warm sea surface temperatures (that aid convection) are conducive for further development.

Global models, according to the JTWC, would seem to suggest a continued track to the West (away from Karnataka-Goa coasts) into Monday winds remaining at 46 km/hr.

During this period, the potential for development of a 'significant' weather system (depression or above) is assessed as low, though it does not seem to rule out scope of intensification later.  

It is in this context that the outlook by the IMD, in whose jurisdictional waters the system lies, that the system would get 'more marked' (intensification by a round to a well-marked 'low') has to be seen.  The IMD also has picked out a trough (an elongated area of low pressure) popping up afresh over the Bay of Bengal linking its South-West Bay of Bengal (off Tamil Nadu) to the Sri Lanka coast.

Atmospheric river

The trough acts as an atmospheric reservoir to store moisture mopped up by the easterly winds from the Bay of Bengal that get piped into the South Peninsula as rain.

The 'low' in the Arabian Sea and the trough in the Bay will combine to trigger fairly widespread to widespread rainfall with isolated heavy falls and thunderstorms, accompanied by lightning, over the entire South India during the next four days, the IMD outlook.

But it singled out South Interior Karnataka and Tamil Nadu for severe weather, predicting isolated heavy to very heavy falls are likely during this period. Fairly widespread to widespread rainfall with isolated heavy falls and thunderstorm and lightning is forecast for Madhya Maharashtra, Marathawada, Konkan and Goa on Monday and Tuesday.

Weather evolving over North-West India and adjoining Pakistan are also relevant in how passing western disturbances, periodical low-pressure waves, could have implications for the Arabian Sea 'low.'

A western disturbance lies already over Jammu & Kashmir on Sunday with its offspring cyclonic circulation having moved in advance, precipitating hail and thunderstorms over parts of North-West India.

Follow up disturbance

A western disturbance 'induces' an offspring circulation to form if it is endowed with the required intensity and depth, in which case it can impact concurrent systems in the Arabian Sea.

The offspring circulation has travelled to the East (ahead of its parent western disturbance) into North-West Uttar Pradesh, even as the IMD has predicted a follow-up disturbance to arrive.

Meanwhile, the IMD has pointed to a situation where the current 'low' over the Arabian Sea weakens and being replaced a counterpart 'low' being sent in from the Bay of Bengal. It would cross the peninsula and step in into the Arabian Sea, bringing another wave of heavy to very rainfall over the South Peninsula and especially along the West Coast later during this week.

Click here to read the Numerical Weather Prediction forecast

The emerging situation is best captured by the US National Centres for Environmental Prediction citing a prospective 'low' passing over Sri Lanka, South Peninsula and Lakshadweep in the first week of November.

 

Detailed IMD forecast for Sunday said that heavy to very heavy rainfall lash isolated places over South Interior Karnataka, Tamil Nadu, Puducherry, and Kerala. It would be heavy at isolated places over Chhattisgarh, Madhya Maharashtra, Marathawada, Konkan & Goa, Coastal Andhra Pradesh, Telangana, Rayalaseema and North Interior Karnataka.

Thunderstorms are likely over Madhya Pradesh, Vidarbha, Chhattisgarh, Bihar, Jharkhand, plains of Bengal,  Odisha, Madhya Maharashtra, Marathwada, Konkan & Goa, Coastal Andhra Pradesh, Telangana, Rayalaseema, Karnataka, Tamil Nadu, Puducherry, and Kerala.

Squally weather with winds reaching speeds of 55 km/hr are likely over East-Central Arabian Sea and adjoining Maharashtra-Karnataka-Kerala coasts. Fishermen are advised not to venture into these areas.

An extended outlook from October 25 to 27 said that fairly widespread to widespread rainfall with isolated heavy falls are likely over south India while it wold be scattered to fairly widespread rainfall over the hills of North-West India (thanks to the western disturbances) and isolated to scattered rainfall over East and North-East India due to their track to the East.

Published on October 20, 2019
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