The state of Tamil Nadu does not receive much rainfall during the Southwest Monsoon season. The reason for very little rains over the state is as Tamil Nadu is a rain Shadow area and is also the least rainy pocket in Peninsular India.
Whenever there are active Monsoon conditions over for the parts of the country, rainfall activity is less over Tamil Nadu. However, during break Monsoon or weak Monsoon conditions rainfall activity is seen to be on the higher side over Tamil Nadu. In fact, even when rainfall activity is limited to some pockets, Tamil Nadu does receive rainfall activity then.
During this time, easterly systems develop along the coast which give rains over the state of Tamil Nadu.
This Monsoon season, no typical break Monsoon condition have been seen. Monsoon however was weak on some occasions in a few pockets.
Even presently, Monsoon activities is limited to a few pockets due to which rainfall has been observed over Tamil Nadu.
Correlation between country wide rains and state rains do not exist as far as Tamil Nadu is concerned.
During 2009, the country witnessed a deficiency of 22% wherein rains were normal for Tamil Nadu. The year 2016 had normal rains for the country while Tamil Nadu was deficient by 20%.
So far, the state of Tamil Nadu has been deficient by 8% which is not an alarming situation as such. However, even though the state is in the normal range, deficiency prevails in many districts of the state even now.
The city of Coimbatore presently is 368 % surplus while Tirupur is 52% deficient which shows the variation of rainfall which has been observed within a radius of 50 km only.
The state of Tamil Nadu has been seeing rains due to the system over the coast. Also, a cyclonic circulation is persisting off the coast of Tamil Nadu which has been causing rainfall over Tamil Nadu and adjoining areas specially over the northern half. Even now, rainfall activity will continue over the state of Tamil Nadu for some time.
Courtesy: skymetweather.com