What is Fujiwara Effect?

In the Philippines, many of us have heard the term Fujiwara Effect since Super Typhoon Peping came back when it was supposed to be out of the country. This behaviour is called Fujiwara Effect.

But what is exactly the Fujiwara Effect means? The effect is named after Sakuhei Fujiwhara, the Japanese meteorologist who initially described it in a 1921 paper about the motion of vertices in water.

Fujiwhara effect or Fujiwara interaction is a type of interaction between two nearby cyclonic vortices, causing them to appear to "orbit" each other. When the cyclones approach each other, their centers will begin orbiting cyclonically about a point between the two systems. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it.

The effect is often mentioned in relation to the motion of tropical cyclones, although the final merging of the two storms is uncommon. The effect becomes pronounced in these storms when they approach within about 1,450 km (900 mi) of each other and are at tropical storm strength or stronger.

Source: http://en.wikipedia.org/wiki/Fujiwhara_effect