As Tamil Nadu braces for Nivar that is expected to cross its coast as a very severe cyclonic storm, records over the past two decades show that many of the storms that moved west-northwestwards had yielded a good amount of rain at the time of their landfall.
Senior meteorologist Y.E.A. Raj said nearly 13 systems crossed the Karaikal-Mamallapuram belt in November and December during the period from 1971 to 2019. A cyclonic storm in 1994 originated in the same location as Cyclone Nivar and yielded a good rainfall. Nivar will be a rain-filled storm, too, and is likely to cross south of Chennai, around Puducherry.
There were exceptions like Cyclone Nilam that made a landfall close to Kalpakkam at the end of October 2012, with a lesser intensity and causing less damage, Mr. Raj said.
Meteorologists and weather bloggers draw a parallel between the current cyclone and Cyclone Nisha that crossed the coast close to Nagapattinam, taking a similar direction. Nisha had formed on November 25, 2008, and brought heavy rain in some districts — Nagapattinam, 57 cm, and Cuddalore, 44 cm — until November 28.
Weather blogger R. Pradeep John, who runs the popular Tamil Nadu Weatherman blog, said slow-moving cyclones had given good rain in the past. Cyclone Nisha had moved northwestwards, like the present system, and gave 40 cm of rain to Chennai. The city has already received close to 20 cm over the past two days from Cyclone Nivar.
Though Cyclone Vardah (December 2016) that made a landfall close to Chennai as a very severe cyclonic storm is remembered for its extensive wind damage, it did bring good rain to some areas on the city outskirts and interior areas like Vellore, he said.
The bloggers pointed to the other very severe cyclonic storms that passed by the Tamil Nadu coast. K. Srikanth of the Chennaiyil Oru Mazhaikalam weather blog said Cyclone Ockhi, which formed on November 29, 2017, damaged rubber plantations and banana crops in Kanniyakumari and left several fishermen missing.
Similarly, very severe cyclonic storm Gaja (November 2018), which had a devastating impact on the delta region, battered such interior areas as Tiruchi, Dindigul and Kodaikanal, he said.
As Nivar drew closer on Tuesday, several areas in and around the city received steady rain. Nungambakkam received a heavy rainfall of nearly 11 cm between 8.30 a.m. and 7 p.m.
The Water Resources Department is closely monitoring the storage in city’s four reservoirs.
The level in the Chembarambakkam reservoir was at 21.38 feet, against the full level of 24 feet, at 10 p.m. It had increased by 0.06 feet from the level recorded at 6 p.m. The lake received 729 cubic feet per second (cusecs) and the storage was at 2,955 million cubic feet (mcft) against its capacity of 3,645 mcft.
The other three major waterbodies still need nearly 1,000 mcft each to fill up.
In Kancheepuram and Chengalpettu districts, of a total of 909 tanks, nearly 134 tanks, including Sembakkam and Nanmangalam, have filled up. A total of 231 tanks touched 75% of their storage.