San Francisco Frontiers - Tamil Nadu and Puducherry Face Return of Very Heavy Rain

Tamil Nadu, Puducherry and Karaikal may receive isolated rainfall of 11 to 20 centimetres on Tuesday and Wednesday, according to the latest weather outlook.

Isolated very heavy rainfall of 11-20 cm is likely over Tamil Nadu, Puducherry and Karaikal on Tuesday and Wednesday as the north-east monsoon approaches the end of its first week over the South Peninsula, with an easterly wave seen feeding dense rain clouds into the region.

Satellite imagery on Tuesday morning indicated heavy cloud bands clustered over the Palk Strait, spilling from the Jaffna peninsula in northern Sri Lanka across the sea towards Kumbakonam and Mannargudi in Tamil Nadu.

The cloud mass forms the leading edge of an easterly wave extending from Sumatra and the Gulf of Thailand, with moisture-laden clouds building in masses over the central parts of the south-west Bay of Bengal off Sri Lanka.

Outlook for Chennai

Chennai faces a stop-start rain outlook on Tuesday. Some thundershowers are possible in the morning, but skies are projected to clear by noon, with the probability of rain falling to 46 per cent.

Mostly clear conditions may prevail through the afternoon and early evening before thunderstorms return around midnight and persist into Wednesday morning. Bengaluru, at the same time, can expect alternating spells of sunshine and cloud.

India Meteorological Department (IMD ) has forecast a wider spell of wet weather across the region. Isolated heavy rainfall of 6-11 cm is likely over Tamil Nadu, Puducherry and Karaikal for five days from Thursday, and over Kerala and Mahe for seven days from Tuesday.

South Interior Karnataka is in line for four days of heavy rain from Wednesday, while South Coastal Andhra Pradesh and Yanam may receive heavy showers on Tuesday and Wednesday, followed by Rayalaseema on Wednesday.

Kozhikode pelted

Lakshadweep, too, is forecast to receive isolated heavy rainfall over the five days from Thursday. at the same time, the 12 hours ending Tuesday morning offered a measure of the developing wet spell: Kozhikode in Kerala recorded 10 cm of rainfall, while Tondi in Tamil Nadu received 5 cm.

The immediate weather driver is a cyclonic circulation over the south-west Bay of Bengal, off southern Tamil Nadu. By drawing moist air together and encouraging it to rise, the system can sustain cloud bands and trigger thunderstorms over the sea and adjoining land. Its proximity to the Tamil Nadu coast makes the state, among them its southern districts, particularly vulnerable to repeated spells of rain.

Troughs, circulations

A trough extending from this circulation towards the north-west Bay of Bengal broadens the zone of moisture convergence and cloud development. Tamil Nadu and Puducherry are likely to bear the most direct influence, with repeated showers and thunderstorms and the potential for localised heavy to very heavy downpours. The eventual distribution and intensity will depend on how long the circulation persists and how it moves.

Further west, an upper-air cyclonic circulation over North Interior Karnataka could support organise moisture convergence and showers over the state’s interior and neighbouring parts of the Deccan. The alignment of the Bay-side trough will influence how far the rain spreads into adjoining districts.

A separate trough extending from south-west Rajasthan to the north-east Arabian Sea could support localised clouding and convergence over parts of western India, bringing showers and thunderstorms, with isolated heavy spells where conditions favour stronger development.

Outlook for Bay churn

The Bay of Bengal could likely hold the next weather trigger. A cyclonic circulation persists over the Gulf of Thailand, a region from which weather disturbances can move westward towards the Andaman Sea and the Bay of Bengal.

IMD numerical model guidance points to the possibility of intensification of the system over the Bay waters, although the system’s eventual development and track will determine whether it translates into a fresh spell of rain over the South Peninsula.

I.Wright--SFF