“Amphan” (pronounced UM-PN) had turned into an extremely severe cyclonic storm and gathered more strength over the Bay of Bengal while moving slowly towards the coast. It has now intensified further into a super cyclonic storm, the India Meteorological Department (IMD) said.

For active cases per lakh population, the critical threshold would be when more than 15, while for doubling rate calculated over a seven-day period, the critical level would be less than 14 days and desirable when more than 28 days.

As for case fatality rate, more than six per cent would be considered critical and less than one per cent desirable. The critical threshold for testing ratio (number of tests per lakh population) would be less than 65 while the desirable level would be more than 200, according to the letter.