Updated: October 17, 2020 7:47:11 am
A man struggles to stay afloat in a torrent of water after heavy rains in Hyderabad, on October 14 (Photo: PTI)
Earlier this week, three days of extremely heavy rains caused massive flooding that killed more than 70 people in Telangana, Andhra Pradesh and Maharashtra. Hyderabad recorded its rainiest day in 117 years, flooding more than 20,000 houses. In Pune, Sangli and Solapur, almost 20,000 people were evacuated.
This was caused by weather that formed in the Bay of Bengal, hit the east coast and moved west, weakening along the way. On Friday, it reappeared in the Arabian Sea and will intensify further as it moves out to sea.
Trip
On October 9, a low pressure system was developed in the North Andaman Sea. During its journey towards land, it intensified several times, first to form a well-marked low-pressure area, then a depression, and then a deep depression while at sea. Low pressure area, depression, and deep depression are part of a classification based on wind speed.
On October 13, the system crossed the land near Kakinada, Andhra Pradesh, as a deep depression. As the system moved west-northwest, it brought extremely heavy rains across Telangana and some parts of Andhra Pradesh on October 13-14. In the last 48 hours, the system weakened and spread across southern Madhya Maharashtra, causing widespread heavy rains in several areas of Maharashtra. Early Friday, the system left the west coast.
From coast to coast, the journey
Record rainfall
Hours after the deep depression hit land, both Andhra Pradesh and Telangana experienced extremely heavy rains. The 24-hour rainfall that ended at 8.30am on October 14 recorded in the city of Hyderabad was 191.8mm. This is the heaviest spell Hyderabad has ever experienced in October. The previous record was 117.1 mm on October 6, 1903. Many districts throughout the central and western regions of Telangana received excess rainfall – 150% to 400% above normal during the first half of this month. . Hyderabad district was 411% above normal.
MET officials noted that the rainfall was not very high compared to the rainfall that is received during the southwest monsoon. However, when these episodes occur in such a short time in October, they are largely associated with low-pressure systems and cause urban flooding.
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Why was it so severe
Typically, cyclones lose strength when they hit land. This particular system, however, marked a long east-west path through Andhra Pradesh, Telangana, the northern interior of Karnataka, and Maharashtra.
“All of these states experienced above-normal rainfall during the recent monsoon season. As a result, the soil in these regions has retained significant moisture content … The high availability of moisture even on land propagated this large embedded system throughout its trajectory so far, ”said Mrutyunjay Mohapatra, Director General of the Meteorological Department of India (IMD).
Additionally, vertical wind shear, resulting from a significant difference in wind speed between the highest and lowest atmospheric levels, helped the system maintain its intensity as a deep depression or well-marked low-pressure area even on land. , He said.
Flood water flows through a street after heavy rains, in Falaknuma, Hyderabad, on Wednesday, October 14, 2020 (PTI photo).
There are two seasons, March-May and October-December, in which cyclones or depressions form in the northern Indian Ocean (the Arabian Sea and the Bay of Bengal). The last season witnessed four of the five cyclones that form in this region each year. Therefore, the formation of the current depression or low-pressure system is common, Mohapatra said.
In fact, the strongest systems – Cyclones Phailin (2013) and Hudhud (2014) – formed in the Bay of Bengal had made landfall in October, when the retreat from the southwest monsoon was still ongoing.
On his last legs
On Friday, the well-marked low-pressure area was over the east-central Arabian Sea, off the coast of Maharashtra. By Sunday, IMD officials said, the system would consolidate into a depression as it continued to head west. Fishermen have been advised to stay away from the sea until October 19.
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