The southwest monsoon has set in over parts of southeast Bay of Bengal, the Nicobar Islands and the Andaman Sea on Thursday, at least eight days ahead of schedule. The India Meteorological Department (IMD) said in its update that conditions were favourable for its further advancement over some more parts of Andaman Sea and southeast Bay of Bengal during the next 48 hours.

The Bay of Bengal arm of monsoon normally breaks around May 18-20, followed 10-12 days later by the counterpart Arabian Sea arm along the southwest coast of the mainland. The onset over intervening Sri Lanka takes place roughly midway between.

According to the European Centre for Medium-Range weather Forecasts (ECMWF), the `low' will later move in a north-northeast direction and make a landfall along the West Bengal coast by May 17. Weathermen say there is no guarantee that the Arabian Sea branch of monsoon will retain the eight-day lead of its counterpart, but there are indications that the southwest Indian Ocean may be bracing to guide a barrage of cross-equatorial monsoon flows off the east African coast into the Arabian Sea.

The ECMWF said in its six-day outlook that the cross-equatorial monsoon flows may pick in strength around May 18, culminating in a blow-up near the Horn of Africa (Somali coast) two days later. This could well be the trigger the system needs to heave itself forward to the Kerala coast.