THIRUVANANTHAPURAM: The Indian Meteorological Department (IMD) on Saturday said that the Northeast monsoon, which is also known as Thulavarsham, has strengthened over coastal areas of Tamil Nadu, Puducherry and Karaikal and southern parts of Andhra Pradesh. Kerala is likely to receive isolated rain till Friday due to northeasterly winds formed over the Bay of Bengal. Southern districts may experience rain accompanied by thunder and lightning. A yellow alert has been sounded in Kollam, Pathanamthitta, Alappuzha, Kottayam, Idukki and Palakkad districts today.