What Happens When Two Hurricanes Collide?
Because 2020 is, you know, 2020, there is the possibility of two hurricanes hitting the same spot after riding through the Gulf of Mexico mere hours apart. This begs the question, what happens when two hurricanes collide?
If this sounds nightmarish, it is not as bad as you think and it has happened before, though the occurrence is extremely rare.
Tropical Storm Laura and Tropical Storm Marco have the possibility of interacting with each other in a phenomena known as the Fujiwara Effect.
The Fujiwara Effect
Sakuhei Fujiwhara was a Japanese meteorologist who lived at the turn of the 20th century. He was one of the first people to put forth the idea that two cyclones could potentially collide and interact with one another and came up with a credible scientific model as to what that event might look like.
It is important to note that Fujiwhara lived and worked in a time long before satellites. He first put forward the idea of two cyclones interacting and merging in a paper he wrote in 1921. He had no access to the suite of advanced technology and tools that we use today to accurately predict cyclonic behavior. He worked on physics, barometers and observation alone with no help from space.
The Fujiwara Effect calls for two cyclones interacting when they come too close to one another. They can begin interacting within 1,400km of one another and as they draw closer the interaction gains steam and becomes more powerful.
Due to the rotation of the Earth and the rotation of the cyclonic centers, the two systems will slowly begin to try and rotate around one another. The more powerful cyclonic center, usually the one with the stronger low pressure and not necessarily the larger system, will begin to dominate the other.
Usually, this leads to the weaker low pressure system being sheared by the more powerful air flows from the stronger system and the shear will usually destroy the system’s center.
In rare cases, the two systems can merge together and reform into a broader cyclonic system but shearing is the most common outcome.
Laura and Marco
Will Laura and Marco interact in this way? Probably not. There are too many inhibiting factors that is going to prevent this effect from taking place in the Gulf of Mexico.
The distances look correct. Technically, tropical cyclones can begin interacting within 1400km which is roughly 860mi. Right now, the rough estimates, have the storms about 600 miles apart on Tuesday, August 25th, 2020. This is more than close enough to cause the effect to come into question.
So what’s holding it back?
First, Tropical Storm Marco is going to be too close to land. While these two storms will be very close to one another at some point, by the time they approach one another, Marco will be prepared to make landfall. This does not give the cyclones time to begin interacting in any meaningful way.
Second, at this point we do not know how organized these storms will be when they are at their closest point to one another over open water. The forecasts for both Marco and Laura are unclear and there is a chance that one or both of these storms do not have defined centers or strong rotation in their cores at this time. In fact, both might be Tropical Storms or Tropical Depressions and not hurricanes at all at this point.
Most of the models and examples of successful Fujiwaras occur out in the open ocean where the storms have a lot of time and room to maneuver around each other. As both of these storms are being pushed into the coast of the Southeastern United States, there is not enough room or time for them to interact in any meaningful way.
Either way, there is a chance that a part of the US coast between Houston and New Orleans gets hit by back to back tropical systems which is unfortunate.
Seeing two large cyclonic systems occupy the same space like this is exceedingly rare and it will be interesting to see how it all plays out but it probably will not result in a Fujiwara.
Next time two tropical systems approach one another, remember Sakuhei Fujiwhara and his notion of hurricanes merging out over the open ocean.