Weather systems that escaped IMD radars
01.01.2022
IMD is at the centre of criticisms for failing to forecast Thursday’s brought 201. 2mm and 148. 9mm of rain in Nungambakkam and Meenambakkam respectively.
On Friday, IMD officials explained that the previous day’s spell was due to sudden and fast movement of an easterly trough (an elongated region of low pressure) from Bay of Bengal to the city which the ground and satellite-based observation instruments failed to pick up.
The trough, which was originally expected to bring heavy rainfall to districts south of Chennai on Friday, carried rain-bearing clouds with it. These clouds stationed over the city bringing continuous heavy spells. The city, which already recorded 9% excess rainfall during the June-September season (500. 2mm), has added 1360. 4mm of rain this northeast monsoon (October-December) season against a normal of 784mm. This is an an excess of 74%, officials said. The state received 59% excess rain this year.
N Puviarasan, director, Area Cyclone Warning Centre, IMD, told TOI the easterly trough extending from south to north Tamil Nadu led to formation of clouds that moved over the city coast and remained stationary. The movement of the easterly trough and the clouds was supported by a westerly trough above it at an altitude of 10km.
“On the eastern side of this trough, there was convergence and on the western side there was divergence. The convergence caused the formation of clouds. The trough and clouds moved fast over the city coast bringing steady heavy spells. None of the ground or satellite observations were able to pick this up,” he said.
The IMD said a dense network of ground-based instruments may improve forecast accuracy but it may still be difficult to forecast the intensity of rainfall over specific locations.
For the next 48 hours, IMD has forecast thunderstorms with heavy to very heavy rainfall at one or two places in the city. Skymet Weather, in its online post, said heavy rainfall may continue over the city till January 1 and may reduce by January 2 and 3.
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