Cyclone Fengal: What is landfall?

Cyclone Fengal (pronounced ‘Fein-jaal’) is a tropical cyclone. Cyclones are large storms that form when water evaporates from the surface of a sea into the air. As it rises, the air cools and becomes saturated with vapour, eventually forming clouds. These clouds and the air circulation around them eventually start to rotate. The warmer the sea, the more powerful the cyclone will be. While these are the basic ingredients, there are many requires for a cyclone to form.

Once it’s fully formed, all tropical cyclones (in the northern hemisphere) have a complex 3D structure. At this point it has two important features, among others: the eye and the eyewall. The eye is the small centre around which the cyclone rotates. It consists of cold air descending from the cyclone’s top with warm air rising in a spiral around it. The eyewall consists of high thunderstorms that bring rain, lightning, and powerful winds.

These storms may also have large cloud tops — called a central dense overcast — that obscure a view of the eye as seen from above. These clouds appear as a bright disc in radar images.

As long as the cyclone moves over water, it can draw more moisture from below to produce new clouds and rain events around it. But when the storm crosses over onto land, its moisture supply declines drastically and the cyclone weakens. Landfall is the moment in a tropical cyclone’s life when its eye moves over land.

The stormy weather brought by the tropical cyclone is stronger around the eye, so landfall events are potentially deadly because they expose human settlements on land to strong winds and heavy rain. Their effects can be compounded by storm surges that flood coastal areas and prevent inland areas from draining normally. Fortunately, because the air over land is drier, among other factors, the cyclone rapidly weakens.

Depending on environmental conditions, it may dissipate completely or it could pass over land and reemerge on the other side. In 2021, Cyclone Tauktae made landfall in Gujarat and almost reached New Delhi. Later the same year, Cyclone Gulab made landfall over the coast of Andhra Pradesh on September 26 and weakened as it moved across peninsular India. The system reemerged on October 1 as Cyclone Shaheen in the Arabian Sea and two days made a second landfall over Oman.

Tropical cyclones that move sufficiently fast may develop a process called an eyewall replacement cycle: a ring of thunderstorms takes shape at the cyclone’s outer edge and slowly moves inwards to choke the ‘inner’ eyewall. This interaction weakens the cyclone. If the outer eyewall manages to completely replace the inner eyewall, the cyclone may reinvigorate itself.