Many parts of southern peninsular India are already experiencing pre-monsoon showers accompanied by thunder and lightning. File Photo The Southwest Monsoon is most likely to make a timely onset over the Andaman Sea around May 20, the India Meteorological Department (IMD) said Thursday. “The Southwest Monsoon onset is likely over parts of the South Bay of Bengal, the Andaman Sea and the Andaman and Nicobar islands towards the end of the week, May 14-20,” IMD said. The weather bureau said southwesterly winds will prevail during the third week of May and strengthen at lower and mid-level tropospheric latitudes along the Bay of Bengal-Northeast India boundary.…