The Fujiwhara effect: When cyclones ‘dance’

Source: The post is based on the article “The Fujiwhara effect: When cyclones ‘dance’”  published in Indian Express on 24th August 2023.

What is the News?

The western coast of the United States recently experienced Hurricane Hilary, which transformed into a sub-tropical storm upon reaching the US.

This event led to the National Hurricane Centre (NHC) issuing its inaugural tropical storm watch for certain areas of Southern California.

California had an exceptionally wet winter with multiple ‘atmospheric river’ storms, and the area also witnessed the intriguing phenomenon of the ‘Fujiwhara effect’ during one of these storms, where two low-pressure areas interacted in an unexpected manner.

What is the Fujiwhara effect?

As per the National Weather Service (NWS), when two hurricanes or cyclones spinning in the same direction are brought close together, they begin ‘an intense dance around their common center’ – this interaction between two cyclones is called the Fujiwhara effect.

Fujiwhara effect was identified by Sakuhei Fujiwhara, a Japanese meteorologist whose first paper recognising the Fujiwhara cases was published in 1921. 

The first known instance of the effect was in 1964 in the western Pacific Ocean when typhoons Marie and Kathy merged.

What happens in the Fujiwhara effect?

According to the National Weather Service, one of three things happen when the storms come near each other:

– If one hurricane is a lot stronger than the other, the smaller one will orbit it and eventually come crashing into its vortex to be absorbed (or)

– If the two storms are close to the same size, they can gravitate toward each other until they reach a common point where they either merge or they spin each other around for a while before they spin off in different directions (or) 

– If the two hurricanes are intense enough, they may merge with one another, leading to the formation of a mega cyclone capable of wreaking havoc along coastlines.