CHENNAI: The well-marked low-pressure area over Gulf of Mannar and neighbourhood brought substantial rains to north, south, and central districts of Tamil Nadu, with Manalmedu in Mayiladuthurai district topping the list with a whopping 249 mm (24.9 cm) in a 21 hour-period starting 8.30 am on December 12 (Thursday).

According to data from Chennai's Regional Meteorological Centre, Tirunelveli, too, received extremely heavy rainfall (more than 204.mm). The weather station in the southern district recorded 203.5 mm (20.3 cm) from 8.30 am on December 12 to 5.30 am on December 13.

The automated weather station (AWS) in Mayiladuthurai town also recorded very heavy rainfall of 190.5 mm (19.5 cm), while Aduthurai-AMFU in Thanjavur, Karaikal, and Ariyalur districts recorded very heavy rainfall (more than 150 mm), recording 183.5 mm (18.3 cm), 181 mm (18.1 cm), and 173 mm (17.3 cm), respectively.

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Several other southern districts, too, received very heavy rainfall, including Kovilpatti AMFU (138.5 mm), Virudhachalam KVK (124 mm), Kamudhi in Ramanathapuram (119 mm), and Poonamallee in Tiruvallur (116.5 mm).

How much rain did Chennai receive on Thursday

The weather station in Anna University recorded the highest rainfall in the State capital with 87.5 mm (8.7 cm) of rainfall, followed by Meenambakkam with 85.8 mm.

Taramani received 71 mm (7.1 cm), followed by Nandanam and VIT Chennai, which received the least amount of heavy rainfall at 66.5 mm (6.6 cm) and 61.5 mm (6.1 cm), respectively.

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The India Meteorological Department (IMD) defines rainfall categories as:

-- Heavy rain: 64.5–115.5 mm

-- Very heavy rain: 115.6–204.4 mm

-- Extremely heavy rain: 204.5 mm or more