As the heavy rain regime triggered by an erstwhile depression shifted base from North Tami Nadu and interior to South Tamil Nadu and adjoining Kerala, weather watchers are monitoring the behaviour of a fresh low-pressure area that popped up over the South Andaman Sea and adjoining Thailand coast as predicted on Saturday.

The Regional Specialised Meteorological Centre of India Meteorological Department (IMD) says that most weather models indicate that the ‘low’ would move along a typical West-North-West track and concentrate into a depression over the North Andaman Sea by tomorrow (Monday) and reach the Andhra Pradesh coast by Thursday.

Varied outlook by models

However, there is large variation among various models with respect to intensification of the system. The IMD-Global Forecast System and the NCMRWF-Unified Model of the New Delhi-based National Centre for Medium Range Weather Forecasting (NCMRWF) see intensification of system into a tropical cyclone (beyond depression and deep depression status).

The European Centre for Medium-Range Weather Forecasts and the US National Centre for Environmental Prediction-Global Forecast System, however, do not expect intensification beyond a depression (of the same status as the storm that hit the Chennai coast last week). The depression has since weakened into a low and a cyclonic circulation on Sunday.

Given this, the New Delhi-based Centre has arrived at a consensus position that puts the ‘low’ on a track to West-North-West into the East-Central Bay and progressively into the West-Central Bay where it would concentrate into a depression and likely undergo another round of intensification (deep depression and possibly a cyclone) and reach near Andhra Pradesh coast.

Environmental factors

This forecast is due for an update later this (Sunday) morning. Sea-surface temperatures (SSTs) have slightly cooled along the coastline in the aftermath of the heavy rain triggered by the predecessor depression. Wind shear values are favorable as of Sunday and outlook too is favourable along at least the South Andhra Pradesh coast, though these could change.

The Chennai Meteorological Centre of the IMD said that the North-East monsoon has been vigorous over Kerala on Saturday with heavy to very heavy rain being reported from South Kerala. This is expected to continue on Sunday with the IMD declaring an orange alert in Thiruvananthapuram, Kollam, Pathanamthitta, Alappuzha, Kottayam, Idukki, and Kasaragod districts.

Kerala government authorities are closely watching inflows into the Mullaperiyar reservoir in Idukki district and checking whether they would need to open the downstream Idukki reservoir for a second time during this season. Saturday saw rainfall occur at most places over Kerala, South Interior Karnataka, Coastal Andhra Pradesh, Rayalaseema and Yanam.

Many places over the Lakshadweep area; a few places over Tamil Nadu; and isolated places over Coastal and North Interior Karnataka and Telangana also received rainfall during this period. Very light rainfall occurred over Karaikal area.

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