Posted on Sunday Evening:

A Low has formed just W/SW off Sri Lanka in the Gulf of Mannar. The Low, 1006 mb at sea level, extends up to 700 mb levels. This Low, is embedded in the "extended " LWD in the Central Peninsula regions. 
Heavy rains, 30/40 mms,  are expected on Monday and Tuesday in Southern TN regions of Kanyakumari, Tirunelveli, Ramnathpuram and Tuthukodi. Southern Kerala , including Thiruvananthpuram Kollam and Kochi ( 20-30 mms, and 50 mms in Western Ghats of Kerala) will get heavy thunder showers.

Now, seeing the synotic situation and possibilities, we can first safely forecast the Low becoming Well Marked, and moving into the Arabian Sea by Tuesday. 
Currently, dry air, associated with the High Pressure in the Arabian Sea, is blocking the passage onto the Western Arabian Sea region. 
The current flow of 700 mb level, that is the height of the Low, is driving it Westwards, but, on deepening, we may see the NE 200 hp stream dominating. But, the 100 mb stream, now at North blowing dirction, may influence the system to track Northwards.
After Tuesday 6th May, we may see the system moving N/NW, slightly off the coast, till Karnataka coast. Due to strong SW flow at 850 hp levels, it is possible that heavy rains , > 70 mms, will pour along the North Kerala nad Karnataka coasts later in the week. 

Goa may see rains by the weekend, maybe up to 50 mms in a day. We shall review this again.

The next stage will be followed, and the up date after 24 hours , Monday evening.
From Vagaries

#chennai - 3:15pm, #good easterlies and #now feels like N-E #Monsoon. T cells visible over Bay, S-E from city… http://instagram.com/p/nki1gKuqpq/

4:30pm, T showers again over S Tamilnadu and many more over S-central, central Tamilnadu ... http://ow.ly/i/5rZwN
4:30pm, T showers seen over Odisha, N Madhyapradesh, W,central Karnataka, S-W Maharastra, Jharkhand ... http://ow.ly/i/5rZwN

RT @BalaSN: and And it is raining :) #madurai @weatherofindia (3:42pm)
RT @carundev: #SummerRains in #Madurai @keaweather @weatherofindia http://t.co/X4ZE4xybVW (3:58pm)

2:30pm, T showers again over Kanyakumari district (S tip Tamilnadu).
Bay near Tamilnadu coast is active due to circulation and easterlies..
#Chennai - Rain expected towards midnight, early hrs, morning (5-May)

Pre-monsson RF 2014 for TN is still in SCANTY

[1] The Sun is moving in the Northern Hemisphere the land area is quickly heated .  Due to heating at Comorin area and /or near by Mannar bay formation of  WML is evident.

[2] This may give some respite from HOT (mainly heating will be reduced due to cloud coverage and some times rain).

[3] Still the pre- monsoon rainfall for TN is in scanty category.

Gulf Mannar circulation and more rain ahead for S Tamilnadu, S Kerala

RT @shivkswamy:  Yesterday evening there was a tornado like effect with sheets of rain and reduced visibility near Vellore.. driving 10:23am

RT @naveenkumars84: Summer Rains at first day of Kathri Great start.!!! #Chennai #Nolumbur cc @weatherofindia http://t.co/hwhWl5XmPM 10:34am

Low-level circulation over Gulf Mannar persists and will persist during next 2 days ... http://ow.ly/i/5rVZ5 
Due to Mannar circulation, easterlies is pushing moisture into most of Tamilnadu coast and into interior zones !

Scattered T showers expected over most zones of Tamilnadu, #chennai today and tomorrow ! ... http://ow.ly/i/5rW1F 
Especially HEAVY T showers expected for S,S-central,S-W,W Tamilnadu, S,central,N,W-ghats Kerala on today, tomorrow ! http://ow.ly/i/5rW46 
More HEAVY rain ahead for S tip Tamilnadu, S Kerala during next 3 days as the circulation is expected to drift into S-E corner Arabian sea.

#Chennai - RADAR shows showers over W-S-W,W,N-W at around 20 to 60km from city... http://ow.ly/i/5rW8g 

8am, Chennai - showers seen over S-S-E near Mahabalipuram zone. At present wind is from E-S-E, S-E

#chennai - 8:15am, warm #Morning with medium level clouds and a #Thunder cell over E, S, S-E. http://t.co/bCCrdVFJrb