Cyclone Amphan was the costliest tropical cyclone ever recorded in India and the North Indian Ocean, and the strongest cyclone ever since the 1999 Odisha Cyclone. It was the first storm, and strongest of the historic 2020 North Indian Ocean cyclone season, the costliest recorded cyclone season. It made landfall in West Bengal with 100 mph winds. Within India, the storm killed 98 people, and caused $13.8 billion (2020 USD). Amphan produced extremely high winds that ripped roofs off houses and uprooted trees, and storm surges of in areas like Digha, West Bengal.
Background
During 13 May 2020, an area of low pressure developed over the Southeastern Bay of Bengal about to the southeast of Visakhapatnam in the Indian state of Andhra Pradesh.
Over the next couple of days, the system became more marked as it gradually consolidated further, with bands of deep atmospheric convection wrapping into the system's low-level center. During 16 May, the India Meteorological Department (IMD) reported that the area of low pressure had developed into a depression and designated it as BOB 01 while it was located about to the south of Paradip in the Indian state of Odisha. Moving northwards, the depression continually organized and became a cyclonic storm a few hours later, receiving the name Amphan. Due to conductive environments., Amphan underwent rapid intensification into a severe cyclonic storm, with the JTWC assessing an increase in winds from at 12:00 UTC to , the equivalent to a Category 4 hurricane on the Saffir–Simpson scale (SSHWS), just six hours later. Furthermore, the IMD upgraded Amphan to an extremely severe cyclonic storm on their cyclone intensity scale. The broad storm was characterized by a cloud shield extending more than and a sharply-outlined 10 nautical mile-wide eye.
On May 18, the IMD classified Amphan as a Super Cyclonic Storm, with 3-minute sustained winds of 240 kph, reaching its peak intensity later that day.
Early on May 20, Amphan went through an eyewall replacement cycle. Amphan was on a weakening trend. Around 5:30 p.m. IST (12:00 UTC), Amphan made landfall as a Very Severe Cyclonic storm near Bakkhali, West Bengal with winds of . As it moved further inland, Amphan rapidly weakened. Just six hours after landfall, the JTWC downgraded the storm to a Category 1-equivalent cyclone and issued its final warning on the system, as it became disorganized. On 21 May, Amphan dissipated into a well-marked low pressure area.
Preparations
Odisha
The government of Odisha directed the magistrates of four districts on 15 May to establish shelter homes for possible evacuees. Odisha Chief Secretary Asit Kumar Tripathy initially identified 403 possible cyclone shelters in areas potentially impacted by Amphan, though 105 served as temporary medical centres for quarantines associated with the concurrent COVID-19 pandemic. Shelters could only be filled to one-third capacity to maintain social distancing guidelines due to the pandemic.
West Bengal
Social distancing restrictions in West Bengal reduced evacuation capacity in shelters from 500,000 people to 200,000 people. The Kolkata Municipal Corporation located schools and community centres for possible use as temporary shelters to augment evacuation capacity. At least 1,704 shelters were ultimately established in Odisha and more than 2,000 were used in West Bengal, including schools and public buildings. The government of West Bengal planned to evacuate 200,000 people from their homes by 18 May; nearly 300,000 people evacuated in total from the state, including 200,000 from North 24 Parganas district and more than 40,000 from Sagar Island.
Impact
West Bengal
The coastal districts recorded an estimated gusts of .
In Kolkata, reports of car being overturned, trees uprooted and downed power lines caused into havoc. Some parts of the city remained without power. The streets were waterlogged and trees blocking the roads. Some districts got power in the middle of the night after the storm had passed. The airport was remained shut and became waterlogged, many structural damages were reported. Chief Minister Mamata Banerjee even stated that "a bigger disaster than Covid-19". Netaji Subhash Chandra Bose Airport, Kolkata, recorded highest wind speed of 133 km/h on 20 May 2020. Other parts of Kolkata experienced wind speed of 110–130 km/h.