Super Cyclone: A powerful destructive tropical Cyclone "Amphan"

There are two types of cyclones i.e. 1) Tropical Cyclones and 2) Extra-tropical cyclones. Tropical cyclones, as name suggests, forms in tropical region while the extra-tropical form in mid-latitudes. Tropical cyclones are comparatively smaller, longer-lived and are more intense. On 20 May 2020, a tropical cyclone named Amphan made landfall on eastern part of Indian Sub-continent. 

Amphan Cyclone
Image Courtesy: NASA, satellite image from MODIS onboard Aqua satellite

Development:

For the development of a tropical cyclone, following conditions are to be met:

1. This type of storm typically develops over oceans between 10° and 20° N and S latitudes and no closer than 5° from the Equator.
2. Tropical cyclones form over the sea where a threshold sea surface temperature of ~26.5° Celsius is reached. 
3. An unstable environmental lapse rate is also required
4. Weak winds with little change in speed or direction with height are also needed 
5. The atmosphere must have a high-water content through the bottom 5 km of the atmosphere.

Category:

 To assess the intensity of tropical cyclones ranked on Saffir–Simpson scale which rank storms from category 1 (weak) to category 5 (devastating). Amphan has been ranked category 5. The intensity of a tropical cyclone is based on the central pressure of the storm, mean wind speed, and height of the accompanying sea-level rise. Further, Amphan has been classified as "Super Cyclone"; cyclones in the North Indian Ocean with winds surpassing 220 kilometers per hour are considered “super cyclonic”—the highest classification in the north Indian basin. On May 18, Amphan sustained winds of 265 km per hour. Amphan and, the last super cyclonic storm recorded was Odisha in 1999.

Track of Amphan:

Tropical cyclones move from west to east. Amphan made landfall between Digha in West Bengal and Hatiya Island in Bangladesh. After landfall it traversed as shown below. On the approach of cyclone, there is sudden rise of coastal water which is known as storm surge. Storm surge take sea water far inland and cause damage. 

Track of Amphan
Image Courtesy: The Hindu Newspaper, dated 21-05-2020

Destruction:

Since the category of Amphan is 5, devastation is very high wherever Amphan visited, particularly south West Bengal and 24 Pargana district.