The huge cloud mass out into the sea has split up, with a smaller parcel bound for the Puducherry-Karaikudi stretch hitting Cuddalore, Chidambaram, Karaikal, Nagapattinam, Velankanni, and Vedaranyam.

The other big, prominent cloud parcel, is aiming to hit the Mahabalipuram, Sriperumbudur, Chennai, and Nellore stretch later in the afternoon/evening.

Rain, showers

Rain or thundershowers have been reported from Karaikudi, Nagapattinam and Vedaranyam, while Cuddalore and Chidambaram remain partly cloud with thundershowers expected in the afternoon.

Chennai and Sriperumbudur are overcast with possibility of thundershowers in the afternoon/evening, while Nellore in coastal Andhra Pradesh is partly cloudy.

Earlier in the morning, the unified big cloud bank had lain over an area in the sea of a size that would cover most of the South Peninsula from Thanjavur (Tamil Nadu) to Nellore.

An India Met Department update said this (Thursday) morning that the rain-driving 'trough of low' (not amounting to a low-pressure area) remained stationery over South-West Bay of Bengal and adjoining Sri Lanka off the Tamil Nadu coast.

Anti-cyclone

The embedded cyclonic circulation (which helps lift the moisture to the atmosphere, helping it to cool and pour down as rain) keeps shifting coordinates between Sri Lanka and interior Tami Nadu.

The rains will not dry up completely unless the twosome (the trough and the cyclonic circulation it hosts) breaks down. And this will happen with intrusion of dry and cool air from Northwest India.

The intrusion may have started to materialise, but not to an extent that it makes an immediate and sustained impression on the stronger easterly monsoon flows.

At best, they are able to change the direction of the easterlies to being north-easterlies. This helps push rain into South and South Interior Tamil Nadu and adjoining Kerala, as is now clear from weather maps.

Impact on flows

The dry air emanates from an anti-cyclone (rain-suppressing air circulation as opposed to a cyclonic circulation) pushing in from across the Arabian Sea.

The anti-cyclone is forecast to exert comparatively stronger influence over South Peninsula from Saturday on and help dry up rains faster.

Meanwhile, India Met Department has forecast heavy to very heavy rain over Tamil Nadu, Puducherry and Kerala over the next four to five days.

The rains are expected to leave the North of Tamil Nadu and grow to the South in Tamil Nadu and push themselves into adjoining Kerala with the anti-cyclone exerting pressure southward.

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