CHENNAI: With the next extreme weather event likely to hit Chennai and its suburbs on November 10-11, looks like Chennai's 'flood' problem is back again. A red alert has already been issued. With a saturated groundwater table, reservoirs, and lakes near to their brim, it's highly probable that the city's vulnerability will get exposed in the coming days.
The Regional Meteorological Centre (RMC) in Chennai said the low-pressure area that is forming over the southeast Bay of Bengal will become more marked and move towards north Tamil Nadu later this week. Deputy Director-General of Meteorology at RMC S Balachandran said the weather system is being closely monitored.
Most of the weather models, including the Global Forecast System, are suggesting major rains in the Chennai region later this week around November 10. Mahesh Palawat from Skymet Weather said the low-pressure area will intensify into a depression and would cause extreme rains in Chennai and neighbouring districts.
The city received over 21 cm of rainfall on Saturday night. This was the second-highest 24-hour rainfall in a decade for November since the 2015 deluge. Weather blogger Pradeep John on his Facebook post said, "Convergence from Chennai to Cuddalore belt is seen. So there is a chance of heavy rains from Sunday night to Monday morning."
Why MeT department failed to forecast Saturday rains?
Director for TN State Disaster Management Authority N Subbaiyan told The New Indian Express, "We received no rainfall alert from the IMD on Saturday for Chennai. Teams were being geared up to tackle rains forecasted on November 10. Saturday rains caught everyone off-guard."
Green colour coded (no warning, no action) alert was given for Chennai till November 9, though 6 cm to 11 cm rainfall was forecasted for Tiruvallur, Chengalpattu, and Kancheepuram.
Sources told The New Indian Express lack of reliable doppler weather radar was the main reason behind missing the extreme rainfall event. The radar network status page on the IMD website still says Chennai’s rader is unserviceable due to trigger problems and remains offline.
The RMC officials will use the radar installed at the National Institute of Ocean Technology (NIOT) but this radar is still under calibration and testing.
During the pre-monsoon meeting, the State government raised concern over the radar problems with the IMD. Its Director General M Mohapatra then said things were being sorted out and NIOT radar was operational. The government was also ready to help in case of need.
Weather blogger K Srikanth said radar is the best bet for nowcasting. Weather models did not exactly pick a heavy intensity system on Saturday night though they indicated the possibility of heavy rains. "The upper air circulation off the coast of north Tamil Nadu/ south Andhra Pradesh was creating a wind convergence, which triggered thunderstorms on Saturday night," he added.
During a press conference on Sunday, Balachandran said it is not easy to forecast such extreme rainfall when it happens in short bursts. "We can only provide nowcasting, can't forecast rainfall events that occur due to localised factors. Nungambakkam station recorded 21 cm, while Meenambakkam station, which is 20 km away, recorded only 11 cm. It's called Mesoscale phenomenon and is difficult to forecast," he explained.
Areas to be affected
Heavy to very heavy rains are likely to occur at isolated places at Chennai, Tiruvallur, Kancheepuram, Chengalpattu, Villupuram, Puducherry, Cuddalore, Mayiladuthurai, Nagapattinam, Tiruvarur, Thanjavur, and Pudukkottai districts of Tamil Nadu and Karaikal area on November 10