Excess rainfall recorded during the week ending on Wednesday, and a day after on Thursday, has helped Tamil Nadu get into the ‘normal rainfall’ category so far during the ongoing North-East monsoon season. 

But only just, since the normal rainfall category, per India Met Department (IMD) parlance, refers to anything between -19 per cent and +19 per cent of the long-period average.

A single day’s heavy rain on Thursday has knocked three percentage points off the deficit to -16 per cent by the same evening. It was at -19 per cent till Wednesday. 

Deficit districts

The highest deficit (percentage) posted by a district so far is -60 (Krishnagiri), followed closely by -58 (Dharmapuri); -53 (Perambalur); -50 (Vellore); -45 (Chennai); and -39 (Tiruvallur). 

Puducherry has returned a more respectable figure of -6 per cent, with the district of Puducherry at -16 per cent and the district of Karaikal recording +10 per cent. 

These figures were much worse to begin with, since the North-East monsoon had an onset delayed at least by 15 days due to an unseasonal, very severe cyclone ‘Titli’ straying away from Tamil Nadu. 

It took very severe cyclone ‘Gaja,’ and a well-marked low-pressure area that followed, to lend some respectability to the rainfall figures, delivering 49 per cent excess rainfall during the last week. This has continued into Thursday, with good effect. 

Meanwhile, the well-marked low’ has weakened into a conventional ‘low’ and the IMD located it to being over Interior Tamil Nadu and its neighbourhood. The system should continue to deliver more rain during the next couple of days. 

More rain forecast

Fairly widespread to widespread rain with isolated heavy to very heavy falls is likely over Tamil Nadu and South Rayalaseema into Friday. 

It will be isolated heavy over South Coastal Andhra Pradesh and South Interior Karnataka into Friday and isolated heavy over Tamil Nadu and Kerala on Saturday. 

With another week to go, forecasters are watching with interest a couple of tropical depressions in the North-West Pacific for signs of a downstream impact on the Bay of Bengal. 

Only one of these can be of any significance given its track to the west and a landfall over Vietnam, while the other is forecast to move north-north-east and further away into the open Pacific. 

While the IMD is watching the behaviour of a persisting cyclonic circulation over the Malay Peninsula, other models swear by a tropical storm entering the South China Sea. 

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