Isolated Rains likely over North TN

Weather Update

The Northeast Monsoon season, starting from 1st October for data convenience, has got off to a very good start over Tamil Nadu with the seasonal rainfall tally for the 1st 6 days standing at nearly 40% of the October average. Except for Dharmapuri at -43% & Salem at -5% every district in the state is showing positive anomaly so far indicating the widespread nature of thunderstorms during the first week of October. Both the Chennai observatories are nearly at 3 times the long term average with the current accumulated tally for October standing at 9 cms for Nungambakkam & 8 cms for Meenambakkam.

With IMD officially announcing the withdrawal of Southwest Monsoon from parts of Rajasthan & Gujarat it has kickstarted the countdown for Northeast Monsoon. While there is no clear trend from past years in terms of Southwest Monsoon giving way to Northeast Monsoon seamlessly the start of the withdrawal process at least sets the ball rolling. With the way things look we could possibly see quick withdrawal of Southwest Monsoon from most parts of North India & a few parts of Central India as well in the next few days. Subsequent withdrawal will depend on the role a possible post monsoon cyclone, as indicated by weather models to develop in Bay, places in either hastening or delaying the withdrawal of monsoon from rest of India.

While the process of withdrawal happens down south thunderstorms are expected to continue over parts of Peninsular India under the influence of wind instabilities induced by East West Shear Zone type of conditions seen around 5.5 kms ASL altitudes. This zone of instability is seen to persist over North Tamil Nadu & adjoining areas of Rayalaseema & South Interior Karnataka making this region ideal to see some late evening / night thunderstorm activity.

Many places are likely to get light to moderate rains through this thunderstorm activity in North TN one or two places under the right conditions can come under heavy spells at times. Coastal areas like Chennai in North TN will possibly benefit once again from Late night / Early morning thunderstorms which will move along the city & suburbs quickly bringing sudden sharp spell of intense showers which will last for 15 to 30 minutes.