RAIN HAVOC IN CHENNAI. Expected scale-up in rainfall next week may wash clean TN deficit

Despite the strong North-East monsoon, the Met subdivision of Tamil Nadu and Puducherry has returned a deficit of 12 per cent in recorded rainfall during October 1 to November 1.

As per India Met Department (IMD) categorisation, this makes for normal rainfall since percentage departure between +19 per cent to -19 per cent of normal is considered as such.

But Tamil Nadu has improved its position from last week’s low of -21 per cent. The respective figures are -21 per cent for Kerala and +19 per cent for south interior Karnataka.

Rayalaseema has posted excess rainfall of +69 per cent, while coastal Andhra Pradesh languishes with a deficit of -36 per cent. Telangana is at +23 per cent and North Interior Karnataka +31 per cent.

These figures are set to go up during the weekend and into the next, as more rain from strong north-easterly flows lashes the South Peninsula.

On Friday, tropical storm Damrey intensified into a typhoon (cyclone) over the South China Sea, and is expected to hit the Vietnam coast by Saturday.

Importantly, it is travelling in a remarkably straight path to the west, which would take a potent remnant into the Gulf of Thailand and further into the Andaman Sea/Bay of Bengal.

The IMD has already alluded to the formation of the low by November 7-8, which could further add to the North-East monsoon currently lashing the Tamil Nadu coast.

The Damrey remnant would have followed the track of a predecessor ‘low’ that moved into the Andaman Sea this afternoon, and is awaiting traction into the larger monsoon scheme of things.

It would achieve this by establishing a link with an existing and rain-spewing low over South-West Bay of Bengal off Sri Lanka and Tamil Nadu coast.

The rain-generating capacity of a slow moving, even stagnant low such as this is of a much higher order than that of a cyclone as it makes a fleeting run over land.

This is the threat which Chennai and the rest of Coastal Tamil Nadu have to contend with, as was proved in the widespread rain from overnight that has flooded many areas of the metropolis.

This offers a throwback to the conditions witnessed a couple of years ago, although the situation may not have deteriorated to those levels.

What is of concern here is that the existing low would continue to prowl the waters of the Tamil Nadu coast and draw more strength from a low that has moved in from the Gulf of Thailand. The incoming low had weakened into a trough in the Andaman Sea to the extreme South-East of Bay, but enjoys the twin advantages of a leisurely movement and extended onward travel over water.

The stay over water extending into time and space in this manner allows it to grow by ingesting the moisture that associated winds mop up from the sea.

Model predictions also indicate that the current trough could intensify back into a low and merge into the host waiting off Sri Lanka and Tamil Nadu.

This would make for a string of three lows and lead to even more rains for the coast. This is apparently what a weather tracker of the US Climate Prediction Centre points to.

Heavy rain has been forecast for the Tamil Nadu, Puducherry, and South Coastal Andhra Pradesh coasts during the next three to four days.