The anticipated depression sprung up over South-East Bay of Bengal on Wednesday afternoon after erstwhile cyclone Ockhi washed over land to the accompaniment of rains and high winds.
Ockhi delivered moderate to heavy rainfall on the last day of its active life with Dahanu, to the south of Mumbai, receiving the heaviest at 11 cm during the 24 hours ending in the morning. Mumbai-Colaba recorded 8 cm.
Seen weakening
Meanwhile, the Andaman& Nicobar Islands have witnessed heavy rainfall over the past couple of days as a prevailing well-marked low-pressure area over South-East Bay of Bengal intensified into a depression.
An India Met Department (IMD) update located the system to 1,120 km south-east of Machilipatnam (Andhra Pradesh) and 1,200 km south-south-east of Gopalpur (Odisha) on Wednesday afternoon.
It is forecast to move north-west and intensify into a deep depression (near-cyclone) and reach the Andhra Pradesh coast by Friday evening. But the IMD suspected a possibility for slight weakening when it reaches near the coast.
Badly exposed
Evening satellite pictures showed better consolidation of the system compared with the morning, when it lay badly exposed to disruptive winds from a prevailing western disturbance that had earlier accounted for Ockhi.
Flanks to the west, north and north-east were being targeted by the marauding westerly winds from the invader disturbance.
The system presented itself as an elongated mass (rather than circular) of convective clouds. The convection (process of cloud formation) to its East and North were being sheared off, unsettling its structure. But it had managed to mass up better clouding around post-noon. Sea-surface temperatures (28-29 deg Celsius) and some ‘window effect’ to the top are seen helping it to retain some structural discipline.
Squally weather
Overall, prospects of marginal environment and limited development constrained the system, especially the moderate to high vertical wind shear at of 37 km/hr to 55 km/hr (up to 15 km/hr is tolerable).
Vertical wind shear refers to the change in speed and direction of winds with height. High shear values chop the head of the storm tower that rises 10- to 12 km in the case of a full-fledged cyclone.
A warning with respect to squally winds and rough seas are currently valid for the Andaman & Nicobar Islands while fishermen from both the islands and the Tamil Nadu coast on the mainland have been advised caution over the next couple of days.