A deep depression over the southwest Bay of Bengal intensified into Cyclonic Storm, named Ditwah, as of Thursday 11:30 am, an update issued by the Regional Meteorological Centre here said.
The cyclone is moving steadily towards the north Tamil Nadu–Puducherry coast, setting the stage for a prolonged spell of heavy to extremely heavy rain along the coastline over the next three days. It's set to make landfall on Sunday morning.
In its latest bulletin, the Regional Meteorological Centre (RMC), Chennai, said Cyclone Ditwah is currently centered close east of Pottuvil in Sri Lanka — about 610 km south-southeast of Puducherry and 700 km south-southeast of Chennai.
The system is "very likely to continue to move north-northwestwards across the southwest Bay of Bengal & adjoining Sri Lanka coast and reach over southwest Bay of Bengal off North Tamil Nadu, Puducherry and adjoining south Andhra Pradesh coasts by early morning of 30th November," the RMC said in its message.
Forecast models indicate a consistent movement towards the north Tamil Nadu, Puducherry and adjoining south Andhra Pradesh coasts, with landfall or near-landfall influence expected around Saturday.
The system's large wind field and slow progression along the Sri Lanka coast are likely to enhance moisture convergence over the Delta and north coastal districts, raising the risk of widespread flooding in vulnerable pockets.
Rainfall is expected to pick up across the southern and Delta districts, with heavy rain likely in Ramanathapuram, Pudukkottai, Thanjavur, Tiruvarur and Nagapattinam. The core impact period, however, is expected between November 28 and 30.
On Friday, Nagapattinam, Thanjavur, Tiruvarur and Pudukkottai are set to receive heavy to very heavy rain at a few places and extremely heavy rain at isolated locations. Heavy rainfall is also expected in Ramanathapuram, Sivaganga, Tiruchirappalli, Mayiladuthurai, Ariyalur and Karaikal, while Puducherry and Cuddalore could see isolated intense spells.
As the system moves closer to the coast, rainfall intensity will increase sharply over north Tamil Nadu on Saturday. Extremely heavy rain is likely in Tiruvarur, Nagapattinam, Mayiladuthurai, Cuddalore, Villupuram and Chengalpattu, besides Puducherry and Karaikal. Chennai, Tiruvallur, Kancheepuram, Ranipet, Vellore and several interior districts may receive heavy to very heavy rain.
On Sunday, the impact zone will shift to north coastal Tamil Nadu, with Chennai, Tiruvallur, Chengalpattu, Kancheepuram and Ranipet likely to face heavy to very heavy rain.
Coastal areas are likely to experience strong surface winds ranging from 35–50 kmph through Friday. Thunderstorms with lightning are expected at one or two places across Tamil Nadu and Puducherry until December 1.
The RMC cautioned that the evolving system could bring significant rainfall-driven impacts and urged residents to follow local advisories closely.