How weather changed its dynamics to flood in Hyderabad

Hyderabad: Between 14th and 18th October 2020, Telangana's capital Hyderabad received unprecedented rainfall which led to more than 50 deaths and property loss of Rs 670 crore in the city limit. The incessant rains that pounded the city occurred in a non-monsoon month. According to the meteorological calendar beginning, June to September ending are considered to be peak months of the southwest monsoons.

Independent weather analyst Rajanikanth Poolla, analysed the origin, cause of the rainfall.

He explains it will be surprising to note that the foundations of the great deluge in Hyderabad on October 13 was laid as far as in the Pacific Ocean.

Low pressure from the South China Sea entered into East Bay of Bengal near Andaman islands in the 2nd week of October. There are two primary global circulation patterns leading to the current hyperactivity of weather in West Pacific Ocean – La Nina and MJO (Madden Julian Oscillation).

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La Nina is the warming of the ocean and atmosphere over West Pacific and MJO is the periodic phase of significant convection (upward movement of air). Both of them are conducive for tropical cyclone activity over West Pacific and the resultant low pressures often spill over into East BoB.

Low pressures require spending some time over warm waters of the sea to devour on the resources required for their strengthening. This low pressure traveled quickly towards the coast so could not intensify much. Once near the coast it slowed down and intensified into Depression on October 10 and a deep depression by October 12.

Though weather models were increasingly getting ominous about heavy rains in Telangana, it was getting very clear for forecasters by October 11 that Hyderabad city should brace for heavy rainfall from 12 to 14th Oct. As expected, even though the system crossed the coast near Kakinada on October 12 pouring around 200+ mm of rains, it did not weaken much and maintained a highly symmetric circulation pattern up to upper tropospheric levels.

As it moved very near to Hyderabad on October 13, it was still maintaining ‘Depression’ intensity packing highly convective heavy rain-bearing clouds. High convection was evident from significant lightning and thunders too accompanying a steady & the persistent downpour from the afternoon of October 13.