A low-pressure area had formed last night over South-East Bay of Bengal, quite some distance away from the Sri Lanka/Tamil Nadu coasts, an India Met Department bulletin said.
The Met has put it under watch for intensification as a 'well-marked low'. This is the first and basic form of an intensified 'low'.
'Depression' is the intensified form of a well-marked 'low.' A 'deep depression' is the level that will follow and then a cyclone.
It was a deep depression that had entered the coast of Puducherry earlier this week, putting N-E monsoon on a spiral. It had left a larger 'trough' of low-pressure area 'live' in the Bay within which the current 'low' is born.
Over the last five days or so, an amplified trough combined with a prevailing 'low' in Arabian Sea (remnant of earlier deep depression) has been driving rain, setting up flood conditions at many places.
May worsen
These are expected to worsen in view of the creation of the new 'low,' its prospects of intensification over sea, and further intensification as it approaches Sri Lanka/Tamil Nadu coasts.
The excess rainfall trend may last until November 22, forecasts said. The rains may relent somewhat later but may sustain in varying intensities until December 2.
Meanwhile, India Met Department has warned of rainfall ranging from heavy to very heavy and even extremely heavy over Tamil Nadu, Puducherry, Coastal Andhra Pradesh, South Interior Karnataka and Kerala during the next four to five days.
This pertains to the period of intensification of the 'low' out into the sea, its approach towards coast, cross-over into land, and the journey over inland over Kerala and South Interior and Coastal Karnataka).
Rain relents
An India Met update said that scattered to moderate rain lashed parts of Tamil Nadu, Puducherry and Kerala until evening yesterday (Friday).
The proceedings were considerably muted compared to the previous day's heavy to very heavy rains reported from a number of centres in Tamil Nadu, including Chennai and its neighbourhood.
Recorded rainfall (in cm) until 5.30 pm on Friday included Palayamkottai-4; Chennai-3; Kodaikanal, Puducherry, Pampan, Thiruvananthapuram, and Tuticorin-1 each.