Cyclone Burevi that was downgraded to a deep depression on Friday morning and remained stationary over the Gulf of Mannar for several hours further weakened into a depression. Nonetheless, it was one of the unusual weather systems that covered most parts of the State with rain.
It may continue to have an impact over Tamil Nadu, and the spell of rain may last for two more days, even if not of the same intensity. Heavy to very heavy rain may occur in one or two places on Saturday.
As a depression, it will move slowly west-southwestwards across Ramanathapuram towards south Kerala and lose its strength to become a well-marked low pressure area by Saturday.
S. Balachandran, Deputy Director-General of Meteorology, Chennai, said that as the weather disturbance remained stationary for several hours over the Gulf of the Mannar, it pushed moisture into the land and brought heavy rain. The outer feeder bands of the stagnant system brought rain to Chennai, too.
More than 50 weather stations received heavy rain of up to 12 cm during the past 24 hours till Friday morning. A total of 11 stations recorded very heavy rain, and five places received extremely heavy rain of more than 24 cm. Kollidam in Nagapattinam district received 36 cm.
Only the south extreme regions like Kanniyakumari and some Western Ghats areas, including Coimbatore, are yet to get sufficient rain. “In a single day, the weather system helped to bring the State’s rain deficit down to a mere 2% from 12% the previous day. Tamil Nadu’s overall rainfall is now 36.2 cm against its seasonal normal of 37 cm since October 1,” Mr. Balachandran said.
On the heavy rain that extended to the northern parts too, Mr. Balachandran said the vertical wind shear (a sudden change in the direction or the speed over a short distance in the atmosphere) had shifted the rain bands from the main weather system. “This system has extensively covered the central and south parts and also impacted the northern region,” he said.
Chennai and Ennore received 2 cm of rain till 7 p.m. on Friday. The India Meteorological Department has forecast that moderate rain, which may be heavy at times, is likely to occur in Chennai for two days.
Senior meteorologist Y.E.A. Raj noted that this system was unusual in that there were no clouds over the nearest areas like Kanniyakumari or Tirunelveli. There was a disconnect between the centre of the storm and the rain clouds.
Besides the wind shear that pushed clouds towards the north, the weather system too tilted to the north with height owing to a colder temperature prevailing in northern India. “Cyclone Nivar gave rain along its track. This system gave more rain and covered more areas.”
The system was stationary for many hours possibly because it was trapped in the calm region of the upper troposphere, where winds would be weak, he said.