May I have this dance?
For a period in time it looked like that is exactly what we were about to witness between Matthew as it weakened to a Tropical Depression and Tropical Storm Nicole. For a time, the two storms were in close proximity to each other between Bermuda and the Bahamas. If you were to look at some forecast guidance, you may have seen the two storms moving indecently toward each other and then briefly appearing to rotate around each other uniformly. This is known as a binary interaction but most meteorologists may prefer to call it the Fujiwhara effect.
Named after Sakuhei Fujiwhara, a Japanese meteorologist, who noticed the interaction through studying vorticies in water. Yes like any studied meteorologist will tell you, the atmosphere is just one giant fluid with spinning eddies and vorticies. In 1921 on a much smaller scale Fujiwhara noticed that these spinning vorticies in the water would interact with each other when they were certain distances apart. What appears to happen is that the vortices will spin around a center point if they get close enough together. The closer they get then the faster they rotate around that point with a certain distance leading to the two vortices combining into one.
This same interaction is noted when two hurricanes pass within close proximity to one another. It appeared, for a while at least that this would occur with the two recent Atlantic storms but that was noted in a model forecast. Past examples in the Atlantic include Hurricane Iris and Humberto in 1995. In the Pacific in 2005 Tropical Storm Lidia interacted with Hurricane Max and was actually absorbed by the larger storm in the end. In 2009 Typhoon Parma and Melor interacted enough so that the track of Parma was affected as it moved through the South China Sea.
By studying and understanding this interaction computer forecasts can account for this and adjust the track depending on how intense the storms area and how close they will pass to each other. At just under 900 miles apart the effect will become noticeable. If the storm centers continue to get closer then the rotation of the pair increases in speed. If and when the storms get to within 200 miles of each other, then it becomes likely that they will merge into one storm, often the larger of the two absorbs the smaller.
So next time your tracking two cyclones (they don’t necessarily have to be tropical) and you notice they will be close enough then start the music because you are about to witness a dance. Hope they keep it at middle school arms length apart though, if not, then only one cyclone will be leaving that dance later.
