The India Meteorological Department has forecast isolated heavy rainfall over Tamil Nadu, south interior Karnataka and Kerala over the next three to four days, even as the southwest monsoon withdraws from the northwest.

On Monday, the withdrawal line passed through Gurdaspur, Chandigarh, Muzaffarnagar, Aligarh, Dholpur, Udaipur, Deesa and Naliya, marking further retreat across Punjab, Haryana, Delhi, Uttar Pradesh, Rajasthan and Gujarat.

Isolated heavy rain is expected over Tamil Nadu, Puducherry and Karaikal for three days; south interior Karnataka for four days; and Kerala and Mahe for four days from Wednesday. Kerala and Mahe could see widespread showers for three days from Thursday, while coastal Karnataka faces five days of rain from Tuesday. The IMD also warns of thunderstorms, lightning and gusty winds across the southern peninsula.

Why it matters: the wind regime is shifting, with south-westerlies over the Arabian Sea set to give way to easterlies around October 7 — opening the door to a fresh spell of rain even as the monsoon formally winds down.