As expected, a cyclonic circulation has formed over the North Bay of Bengal (BoB). The feature is marked in the lower and middle levels, tilting southward with height. It does not appear to be a strong system and, therefore, may not develop into a low-pressure area on the sea surface. Nonetheless, this weather system is likely to trigger a change in the weather pattern and mark the transition from the southwest monsoon to the northeast monsoon season.
The cyclonic circulation is expected to remain largely over the sea for the next three days. However, it has a tendency to shift southward along the coast of Odisha and Andhra Pradesh during this period. The weather activity may not penetrate deeply inland, yet scattered rain and thundershowers are likely over the extreme southern parts of Gangetic West Bengal and the coastal parts of Odisha and Andhra Pradesh during this time. The activity may later extend to the coastal and interior parts of Tamil Nadu.
It is a little early to say, but this system may become instrumental in ushering the northeast monsoon over the South Peninsula. Typically, the northeast monsoon declaration is not made before 10th October, even if conditions are favourable. The foremost criterion remains the arrival of easterly winds along the Tamil Nadu coast. The visible manifestation of the monsoon comes with an increase in rainfall activity over coastal Tamil Nadu, south coastal Andhra Pradesh, and adjoining areas. Of course, before the announcement, the southwest monsoon must retreat up to 15°N over the South Peninsula.
With the circulation developing over the BoB, the low-level winds have shown a tendency to become easterly over the sea surface and the lower atmosphere as well. Still, the pattern needs to be monitored for a couple of days for continuity. The normal date for the onset of easterly or southeasterly winds is 14th October. Subject to the fulfillment of other conditions, the normal date for the arrival of the northeast monsoon is 20th October. As it appears, the onset may occur earlier than normal this season.
