CHENNAI: The memories of the destruction caused by cyclone Vardah and the 2015 floods began to haunt Chennai residents when IMD forecast Cyclone Nivar to make landfall as a very severe cyclonic storm at an estimated speed of 120-130kmph gusting to 145kmph. But unlike Vardah or Gaja that left a trail of destruction, Nivar, though a very severe cyclonic storm, spared Chennai and the rest of the northern districts it crossed on Wednesday night. According to experts, the damage was comparatively minimal because the cyclone’s structure was disorganised and not compact enough to pack stronger winds that can cause major destruction.
Professor Sridhar Balasubramanian, climate expert from IIT Bombay, said the eye of Nivar was not distinctly visible, which means the storm was disorganised with drastic reduction in the wind speed on the outer edge compared to the speeds in the eyewall, the ring around the eye in the centre. Hence, the damage caused by winds was less.
But storms like Vardah and Gaja were organised and compact with less difference in the wind speeds at the eyewall and the edge of the storm, hence packing stronger winds to cause more destruction when crossing the land. The eyewall usually has the maximum wind speed.
“A storm with a visible eye is dynamically more dangerous as it will be more organised and compact. Nivar was a disorganised storm spread over a larger area from Nagapattinam to Nellore, which means less wind velocity,” he said.
“Land friction caused by topography of Sri Lanka and later the Delta region did not let it Nivar organise in a compact manner,” he said.
He said convective bands of the storm spread over a large area were moving slowly bringing more rain, unlike Gaja or Vardah which moved faster bringing more winds and less rainfall over the land. Further the winds of Nivar were not strong enough to push and cause stronger storm surge.
On Thursday, officials from Regional Meteorological Centre, Chennai, visited ground zero where the storm made landfall to conduct a post-storm survey. N Puviarasan, director, Area Cyclone Warning Centre, RMC Chennai, said interaction with fishermen revealed that the wind speeds were relatively less during landfall than what was anticipated. Though the winds were at a maximum speed of 140kmph over the sea, it reduced during landfall. “Our nearest automatic weather station in Puducherry recorded 50kmph wind speed during landfall. The storm itself had good wind speeds on the eastern side and while it was less on the western part,” he said.
However, experts said the automatic weather station in Puduchery, which is 30km south of the landfall location, is on the ground level where trees and buildings may be obstructing it from capturing the actual wind speeds.
Former deputy director general, IMD, Y E A Raj said the track of Nivar was similar to that of cyclone Nisha in 2008 which formed around the same region and moved northwestwards like Nivar to make landfall near Nagapattinam. The wind speed of Nisha was 83kmph and it brought good rainfall of 55cm over four days. “Nivar has moved over Rayalaseema and has brought a lot of rain on Thursday which is unusual for that region in November-end. On Friday too, there will be more rain as the system is stationed near Rayalaseema,” he said. “But extent of damage caused by Nivar may be known after some time, as even in Gaja, it was initially thought there was not much damage but it later emerged over a period that it caused much more damage than what was expected,” he said.