It is that time of the year when most of Tamil Nadu starts to look for its own “Monsoon”, Northeast Monsoon, while the rest of the country enjoys Southwest Monsoon Tamil Nadu being a rain shadow region thanks to the Western Ghats waits for its turn. The seasons change & the wind patterns turn from Westerly to Easterly to herald the advent of Northeast Monsoon what we like to affectionately call “Chennaiyil Oru Mazhaikaalam”. The normal onset dates for Northeast Monsoon is October 20th with an expected variance of +/- 7 days. A COMK take on the onset of upcoming Northeast Monsoon
After stalling for almost 10 days Southwest Monsoon has further withdrawn almost all of Central India along with whole of Maharashtra and parts of Telengana & Andhra Pradesh in South. Further withdrawal could be expected in the days to come as the wind change has set the wheels in motion for Northeast Monsoon. 
While on the one hand Southwest Monsoon has been keeping up with its schedule despite getting stalled for almost 10 days the key question is would Northeast Monsoon keep up its date of Onset. Last year saw Northeast Monsoon set in with a bang on October 18th with Tamil Nadu receiving widespread rains for the 24 hours ending on 18th October 2014. Chennai saw flooded roads with most areas receiving more than 200 mm rains in less than 48 hours. Will this year see Northeast Monsoon start with a bang like last year?
As things stand it appears this year Northeast Monsoon could miss its onset date of October 20th with possibly a delay of few days expected. While Sri Lanka & parts of South Tamil Nadu could start receiving showers from the Easterlies starting from 18th these are expected to be isolated and scattered. Going by model estimates North Tamil Nadu may have to wait for its turn of fairly widespread showers around last week of October.
Northeast Monsoon could have a subdued onset partially due to the influence exerted by the developing Typhoon “Koppu” over Western Pacific, over the next few days as it moves in a W/NW direction towards Philippines it is expected to change the wind directions over Bay of Bengal from Easterlies to Westerlies preventing the moisture laden winds from the Bay to reach Indian Subcontinent. This could result in possibly dry continental air from Central Asia reaching the Southeast coast of India preventing rainfall prospects. Normalcy in wind directions are expected to be restored once Typhoon Koppu weakens over South China Sea. 
With the absence of any tropical wave activity over Indian Ocean basin local support for the onset of Northeast Monsoon appears weak as well. As things stand we could possibly expect the proper onset of Northeast Monsoon with a delay of possibly 4 – 7 days. As things evolve we would update the developments.