Latest analysis show that the Low pressure system is marching towards Chennai , N-coast Tamilnadu.

The Low will start to push into land thru Chennai, N-coast Tamilnadu and S-coast Andhra during next 24hours

During next 24hours HEAVY widespread rain expected for Chennai , N,central Tamilnadu coast

During next 36hours Heavy rain also for S,central Andhra coast

11:40pm, more sharp showers approaching Chennai city.
Going to be a wet night and into morning as well.

RT @fabwrite: 8pm, Heavy downpour in #Mandaveli #Chennai @chennaiweather @weatherofindia

Chennai - 9:32pm, heavy steady drizzle continue for the past 1hr in Polichalur zone

RT @rajugana: @weatherofindia Bangalore 7.35pm, Today was cloudy with slight drizzles at times. It is raining now.

Ayyampet, Tamilnadu, Tanjore district - 10:50pm, steady drizzle continues

It is raining at Chennai now [201013/2030 hrs IST]

[1] It is raining at most of places in Chennai.

[2] The circulation becomes WML.

[3] It moves in North -NW direction.

The amounts of rainfall realised at 20.10.2013 / 1930 hrs IST is given below:[RF in mm]

(1) Thirukoilur ARG     ..59.0
(2) Cheyyur    ARG     .. 35.0
(3) Vaniyambadi          .. 33.0
(4) Kalavai                     24.0
(5) Ennore                 ..   11.0
In and around Chennai:
{1} HVF AVADI            5.0
{2} ANNA UTY            1.0
{3}KOLAPAKKAM      3.0
{4} CHENNAI [N]         4.0

#Chennai - 6pm, After a long day with Heavy high cloud cover... now sharp showers have pushed into North suburbs of city.

A mini update on present circulation ... http://ow.ly/pZoHs 
Latest analysis about S,S-W Bay circulation and forecast coming up at 9:30pm

5:30pm, Heavy rain over N,N-central, S, central-coast Tamilnadu .. and some along S coast Andhra ... http://ow.ly/i/3txxh 

Bay circulation

As expected the SWM has come down to 14 Deg latitude in Arabian Sea and thence blow as NWly.  The Westerly, SWly winds in Comorin Sea makes circulation in Bay roughly about 440-550 km East /Se of Nagapattinam / Karaikal.  The UAC over Srilanka moved NNW and gave rainfall in southern parts of TN.  The circulation in south central Bay may bring rainfall to Choramandal coast i.e from Vedaranyam to Nellore in south coastal AP.  As pointed out by mentor this can also be considered as 'MONSOON LOW"[Trough].  SST and upper winds are favorable for strengthening of this circulation.  This may bring NEM to TN

Chennai - 1:30am, monsoon is here.. sharp showers now lashing city. Rain moving in from sea, E-N-E.
More showers before morning!