More on the Extreme Rainfall in Kayalpattinam...Some Explanations...

On Sunday (December 17), the Kayalpattinam locality within Tamil Nadu’s Thoothukudi district received a whopping 96 cm worth of rainfall in a single day, much higher than what the district receives in an entire year (up to 70 cm)! This intense soaking is down to several factors.

Typically, heavy rainfall of this magnitude is linked to well-defined systems like cyclones. However, in this instance, it was a mere upper-air cyclonic circulation over the Comorin area that triggered such substantial precipitation.

“There was more moisture inside the system which gave widespread rainfall, but usually upper air circulation doesn’t give this much rain. This (system) has given more rain than a cyclone,” S Balachandran, head of the Chennai-based Regional Meteorological Centre (RMC

This rainfall is both unusual and unprecedented especially when we are in the fag end of the northeast monsoon. Nothing like this has happened in more than 100 years,” said YEA Raj, the former deputy director general of the Indian Meteorological Department (IMD).

The torrential showers in Tamil Nadu's plains on Sunday and Monday constituted one of the highest-ever recorded rainfall episodes within a 24-hour period for the region. While such intense rainfall is more common in hilly regions, it is exceedingly rare in plain areas.

In spite of the unusual downpour, however, it is essential to acknowledge that additional factors may have contributed to this event. For instance, the slow movement of the rain-bearing system over the Comorin area—akin to Cyclone Michaung's stalling near Chennai on December 4—likely allowed repeated convergence at the same location.

Meanwhile, owing to the absence of an IMD observatory in Thoothukudi, the state government's observatory has provided this rainfall data to the National Data Centre in Pune. This data will undergo verification against previous years' records to gain further clarity on the significance of this single-day rainfall event and the records it may have broken.

Excerpt From "The Weather Channel,"