With southwest monsoon withdrawing faster than expected, atmospheric conditions are slowly becoming favourable for the onset of northeast monsoon. However, it will take at least one more week to meet the criteria required for the declaration of the onset of northeast monsoon, also known as Thulavarsham, which is marked by evening thunderstorms and lightning.
According to the onset criteria of northeast monsoon, southwest monsoon should have withdrawn up to coastal Andhra Pradesh. Further, peep easterlies (up to 850 hPa) should have set in over Tamil Nadu or seasonal low should have been established in the South Bay of Bengal adjacent to Tamil Nadu coast. Now the line of withdrawal has almost crossed Maharashtra and parts of Karnataka, and conditions are favourable for the further withdrawal of southwest monsoon from the remaining parts of the country.
Though the eastern parts of Kerala, especially the Ghat region, started to receive isolated thundershowers, these rains are triggered by the remnants of the southwest monsoon and systems over the Bay of Bengal which are likely to continue till the easterlies begin trending towards the southern peninsula. Similarly, the scattered rain witnessed in parts of north India in the past few days was triggered by a western disturbance, said India Meteorological Department (IMD) sources.
