After raining down continuously for more than a day, the villainous cloud mass over Chennai has broken up this morning, leading to reduction in rainfall.

But satellite pictures show another mass of fresh cloud waiting out into the sea not too far from the Chennai-Puducherry coast.

Cloud bank

Earlier in the morning, satellite pictures had shown a semi-permanent and hyperactive cloud system over Nellore-Chennai-Puducherry pouring down its contents over the area.

This heavy bank of cloud was unmoved from the previous day as it lay extended from south coastal Andhra Pradesh, and North and Central Tamil Nadu coast. This is what has now broken up.

But the Regional Met Centre, Chennai, has given out a warning for heavy to very heavy to extreme heavy rain, particularly over North Tamil Nadu, for next four days.

The 'soaker trough' spraying rain into Tamil Nadu, Puducherry and Coastal Andhra Pradesh will continue to say anchored to South-West Bay of Bengal until Saturday, according to global forecasts.

Extreme rain

The extreme heavy rain alert is valid for Chennai, Kanchipuram and Tiruvallur districts. Heavy rain has been forecast for the rest of the state, especially in the delta regions in the South.

The rain-driving trough is a the primitive form of a low-pressure and represents an elongated (unlike circular in a 'low') area of lower pressure.

But it can do much more harm given the right ambient conditions, as has now been revealed.

The trough features a cyclonic circulation moving around Sri Lanka and which is responsible for anchoring the strong easterly North-East monsoon flows, and by extension, across entire Tamil Nadu.

The flows are strongest over the North Tamil Nadu coast which triggered the targeted heavy to very rain over an area from South Coastal Andhra Pradesh to Chennai to Puducherry.

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