Rains for South Peninsula as Bay braces for stormy weather

The India Meteorological Department (IMD) confirmed on Wednesday that a fresh low-pressure area may form over the north Andaman Sea in the larger Bay of Bengal basin on Saturday, the day when, coincidentally, the prevailing south-west monsoon may start to exit from parts of West Rajasthan.

The ‘low’ may intensify and move towards the south Odisha–north Andhra Pradesh coast over the first 3-4 days of next week. Initial indications suggest it may not go set up a tropical cyclone., but the coincidence is meteorologically significant.

As the monsoon begins to withdraw, the atmosphere over the Bay starts preparing for North-East Monsoon, or the monsoon in reverse, over the South Peninsula. The transition usually opens the door to vigorous weather systems over the Bay, bringing rain, thunderstorms and gusty winds to parts of South Peninsula that has witnessed big rain deficit this season.

businessline had flagged the possibility on Wednesday morning, pointing to a storm ‘pulse’ travelling in from the South China Sea. The IMD has now provided the synoptic sequence: a cyclonic circulation over north Thailand is expected to emerge over the north Andaman Sea on Friday, one day ahead of the projected ‘low.’ It could later ‘catch fire’ as the latest, and possibly the last, significant system of the southwest-monsoon season.

The IMD expects isolated heavy rain is forecast over Tamil Nadu, Puducherry and Karaikal and Kerala and Mahe for four days from Thursday. South Interior Karnataka could receive isolated heavy rain for four days from Saturday, while coastal Andhra Pradesh and Yanam and Rayalaseema are expected to see such rain for three days from Saturday.

Telangana could also receive isolated heavy rain for four days from Saturday. Strong surface winds are expected over coastal Andhra Pradesh and Yanam, north interior Karnataka, Rayalaseema and south interior Karnataka for four days.

Thunderstorms, lightning and gusty winds are likely to spread across several parts of the South Peninsula, a familiar signature of the atmospheric handover from the south-west to the north-east monsoon, which normally gets under way by mid-October.

The US Climate Prediction Centre had earlier pointed to a helpful pulse of theMadden-Julian Oscillation (MJO)moving into the Indian Ocean. Such a pulse can provide a favourable atmospheric background for organised convection and storm development over the Bay.

The European Centre for Medium-Range Weather Forecasts (ECMWF) had likewise indicated the possibility of an evolving storm system over the Bay. On Wednesday, a pre-existing ‘low’ watched from over Saurashtra and adjoining north-east Arabian Sea, but its influence may wane as north-westerly winds begin advancing from the arid Pakistan, Afghanistan and Iran and across the Arabian Gulf.

These dry continental winds are a classic ingredient of the withdrawal process. The monsoon trough continued to hold together a semblance of rainy order. Its final plunge into the Bay is suggestive of the next act: a ready-made pathway for the fresh ‘low’ to develop.

A secondary trough extends from north West Bengal towards North Odisha, retaining a vestige of the weakening monsoon circulation. A circulation over the north-west Bay and adjoining north coastal Odisha has merged with this trough.

Elsewhere, cyclonic circulations persist over central Assam and south coastal Andhra Pradesh and adjoining Rayalaseema, adding further support to the evolving weather pattern. Another trough stretches from north interior Karnataka to the Gulf of Mannar through south interior Karnataka and Tamil Nadu, helping sustain the current spell of rain over the southern region.

The 24 hours ending Wednesday morning already produced extremely heavy rain over the hills of West Bengal and Sikkim, with heavy to very heavy rain elsewhere across the region and over Saurashtra and Kutch. Heavy rain was also recorded over parts of North-East India, the plains of West Bengal, Odisha, Bihar, Uttarakhand, West Madhya Pradesh, East Madhya Pradesh, Rayalaseema, Tamil Nadu, Puducherry and Karaikal.