Perfect storm: What is the Fujiwhara Effect?

Geography Atmosphere

Context: Recently, the tropical storm Gardo moved towards typhoon Hinnamnor and became super-typhoon exhibiting Fujiwhara effect.

On September 1, 2022, super typhoon Hinnamnor, the strongest tropical cyclone of the year, was hurtling towards Taiwan from the western Pacific Ocean.
As the two approached each other, they started a dance around the central line between them, showcasing a textbook example of what is known as the Fujiwhara Effect.

It is named after Sakuhei Fujiwhara, a Japanese meteorologist who discovered interaction between two cyclonic vortices when they were close to each other.
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.

The Fujiwhara effect can turn two cyclones into one mega cyclone.
It is any interaction between tropical storms formed around the same time in the same ocean region with their centres or eyes at a distance of less than 1,400 km, with intensity varying between a depression and a super typhoon.
The interaction could lead to changes in the track and intensity of either or both storms systems.
In rare cases, the two systems could merge, especially when they are of similar size and intensity, to form a bigger storm.
It is characterised by an intensity that could vary between a depression (wind speed under 63 km per hour) and a super typhoon (wind speed over 209 km per hour).
When two hurricanes spinning in the same direction pass close enough to each other, they begin an intense dance around their common centre.
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.

The first is elastic interaction (EI) in which only the direction of motion of the storms changes and is the most common case.
These are also the cases that are difficult to assess and need closer examination.
The second is partial straining out (PSO) in which a part of the smaller storm is lost to the atmosphere.
The third is complete straining out (CSO) in which the smaller storm is completely lost to the atmosphere.
The straining out does not happen for storms of equal strengths.
The fourth type is partial merger (PM) in which the smaller storm merges into the bigger one and the fifth is complete merger (CM) which takes places between two storms of similar strength.
During a merger interaction between two tropical cyclones the wind circulations come together and form a sort of whirlpool of winds in the atmosphere.