On rare occasions, regular viewers of weather forecasts notice two tropical cyclones near each other on a weather map. The interaction between the two systems is better known as the Fujiwhara Effect.

If you ever wondered what might happen if these two massive storm systems came too close to each other, you are not alone. This very question has been on the minds of many observers and has been studied extensively by the meteorological community.

It also turned out to be a very valid question since tropical storms that come close enough to each other do start interacting and influencing each other. This phenomenon is called the Fujiwhara Effect (also known as the Fujiwara Effect).

In this article, we will examine what the Fujiwhara Effect is, how it develops, as well as the different potential outcomes that can occur when two storm systems approach each other.

Before we look at how this meteorological phenomenon occurs and the different possible outcomes associated with it, we first need to have a concise idea of what exactly the Fujiwhara Effect is:

Fujiwhara Effect Definition

The Fujiwhara Effect is the phenomenon that occurs when two tropical cyclones rotating in the same direction approach each other. Their centers begin to interact, causing the distance between them to decrease. When the two systems are close enough, they may merge or be deflected away from each other.

For this occurrence to take place, the distance between the two tropical cyclones must be within approximately 1 400 kilometers (870 miles). Within this range, the centers of both storms start to rotate around each other while simultaneously being drawn closer together.

The processes involved in the development and the different outcomes of the Fujiwhara Effect will be discussed later in this post. Before we get to that, however, we need to address and clarify some potentially confusing storm names.

People often get confused or think that hurricanes, cyclones, and typhoons are entirely different storm systems. It can be problematic when describing a phenomenon like the Fujiwhara Effect, and these names get used interchangeably while discussing the event.

They are, in fact, one and the same type of storm. Meteorologists use the umbrella term tropical cyclone to describe all three occurrences.

The only reason these storms have different names is because of their location. Hurricanes, cyclones, and typhoons are named according to the region in which they occur:

• • The storm is called a hurricane when it occurs in the central and eastern North Pacific or the North Atlantic Ocean.
  • The storm is called a typhoon when it occurs in the Northwest Pacific region.
  • The storm is called a cyclone when it occurs in the Indian or South Pacific Ocean.

These locations and naming can vary, depending on each region’s unique classification and naming system.

It is important, though, to remember that all three names refer to the same type of storm system. It means that the Fujiwhara Effect refers to the interaction between the same two storms, whether they are called hurricanes, cyclones, or typhoons.

To learn more about the difference between a hurricane, typhoon, and cyclone, you can read the full in-depth article here.​

The Fujiwhara Effect is named after Japanese meteorologist Dr. Sakuhei Fujiwhara, who first studied and identified the phenomenon in 1921. He was the first meteorologist to determine the tendency of two cyclonic storms to rotate around a common point.

Many factors influence the impact of the Fujiwhara Effect in different situations. We will focus on the most important and common outcomes involving this phenomenon. Typically, three possible scenarios play out:

1. 1. Tropical cyclones of equal size and strength collide and merge.
   2. Tropical cyclones of equal size and strength collide and get diverted.
   3. Tropical cyclones with substantial differences in size collide, and one gets absorbed.

It will become much clearer how these three different outcomes can occur when we look at each one in more detail:

When two tropical cyclones of similar size and strength move close enough to be influenced by the Fujiwhara Effect, they begin to rotate around a common center. As the interaction continues, the distance between the storms gradually decreases until the two circulation centers eventually merge.

Once this happens, a single, larger tropical cyclone forms. The newly formed storm often inherits characteristics from both original systems and can become more powerful than either storm was on its own. The exact outcome depends on a number of factors, including the size, strength, and structure of the original tropical cyclones.

An example of this phenomenon occurred in 1995 when Hurricanes Iris and Humberto interacted in the Atlantic Ocean. As the two storms moved close enough to influence each other, they began rotating around a common center and altered each other’s paths through the Fujiwhara Effect.

Although tropical cyclones of the same size that are subjected to the Fujiwhara Effect often result in the merging and formation of a single cyclonic storm, this is not always the case.

Sometimes, these storms rotate and attract each other for a certain period before being deflected and shooting off in different directions. The significance of this result is that another storm system can dramatically change the projected path of a tropical cyclone.

An example of this outcome occurred when Typhoon Parma and Typhoon Melor interacted in the western Pacific Ocean during 2009. As the two storm systems approached each other, they began rotating around a common center, causing significant changes to their projected tracks before eventually moving apart.

Quite often, though, two cyclonic storms with significant differences in size are subjected to the Fujiwhara Effect. During such an occurrence, the smaller storm is drawn toward and starts to rotate around the much bigger tropical cyclone.

Once the distance between the two storm systems has closed, the smaller tropical cyclone is overwhelmed and entirely absorbed by the strong vortex of the larger storm.

An example of this occurrence took place in 1995 when Tropical Storm Karen was absorbed by the much larger Hurricane Iris in the Atlantic Ocean. As the two storm systems moved closer together, the smaller storm began rotating around the larger cyclone before eventually being completely absorbed into its circulation. This is one of the best-known examples of a weaker tropical cyclone being overwhelmed by a stronger storm during a Fujiwhara interaction.

Although the Fujiwhara Effect does not occur that often and is not well-known, this post clearly illustrated the significant impact it can have when two cyclonic vortices spinning in the same direction start to interact with each other.

This article explained what the Fujiwhara Effect is, how it develops, and the different potential outcomes that can occur as a result of this phenomenon.

Until next time, keep your eye on the weather!