The Sun entered the first degree of Sidereal Libra, thus heralding the North East Monsoon or Thula Varsham, as per Astro Meteorology.
This is the Retreating Monsoon. Coming as a depression from the Bay of Bengal, it takes the moisture laden winds and then sweep down on the Himalayas and Indo Gangetic plains, and then pours over peninsular India ! Mainly caused by the heat generated by the overhead Sun on the Tropic of Capricorn. The places of the Indian Ocean becomes hot and the northern parts of India become cool. Cool winds from the Bay of Bengal cause this and the result is Thula Varsham !
Expected to rain till the end of the sidereal month of Vrischika or Scorpio, NEM is a boon to states like Tamil Nadu. Kerala gets both SWM and NEM !