AccuWeather's Melissa Constanzer explains the complexities of the Fujiwhara Effect and how it can significantly complicate the task of forecasting a storm's path.

The Fujiwhara effect, named after a Japanese meteorologist, describes the phenomenon where two cyclonic storms close to each other begin to rotate around a common center. This interaction can lead to unpredictable storm tracks, posing challenges for meteorologists. The effect is most commonly observed when storms are within approximately 850 miles of each other, and can result in the storms either merging, separating, or one being absorbed by the other, especially if there is a significant size difference between them. 

This effect is not limited to large cyclones; even smaller-scale phenomena like tornadoes can display similar interactions, as captured on camera by meteorologist Tony Labeck. Understanding the Fujiwhara effect is crucial for improving the accuracy of weather forecasts, especially during periods of heightened storm activity.

The Fujiwhara Effect

Check out this. It's two tornadoes doing the tango. In this case, the two vortices in the same storm start to morph into one another as they weaken. It's a rare occurrence that our own meteorologist Tony Labeck caught on camera two springs ago. And while tornadoes are very small scale when we think about the weather as a whole, this kind of gives you an idea of how large storms can interact with one another. In fact, when we talk about larger storms called cyclones, a tango between the two is a studied effect. It's called the Fujiwara effect or can otherwise be referred to as binary interaction. The Fujiwara effect got its name from the Japanese meteorologists that studied the interaction in water with a published paper in 1921. The effect can make forecasting tracks of the storm very challenging. So let's help me break this all down because when we talk with start with these storms here, you have to think about a couple different things. This could be a tropical storm, a subtropical storm, or even an extra tropical storm. In this case, we're using tropical storms here and they have to be less than 850 miles apart or so, generally speaking, when we're talking about tropical systems. What happens is the interaction between the two can actually make them start to rotate around one another. So you can see that circulation. Sometimes they end up branching off on their own tracks after that or they can continue to rotate in space for a while. So that's something that leads to that erratic motion and can make a lot of forecasting very challenging. But that's assuming the storms are the same size. Let's make one a really large storm and a powerful one, another one smaller. When we see this kind of interaction, you can see how the smaller storm gets pulled more by the larger storm and therefore gets absorbed.

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