The Fujiwhara Effect and “will Marco and Laura combine to create a megastorm?”

Two hurricanes. Same time. Same place.
European forecast for Marco and Laura by Monday, August 24th
European forecast for Marco and Laura by Monday, August 24th(
Published: Aug. 22, 2020 at 2:00 PM CDT
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BRYAN, Texas (KBTX) - It has become a common question as two tropical storms, Marco and Laura, tumble toward the United States: will they merge to form one megastorm in the Gulf of Mexico? At this point, it may not seem so unbelievable considering what 2020 has doled out.

Short answer: No.

As Marco and Laura cram into the Gulf of Mexico early in the week, there is a chance they could influence each other. However, as of Saturday afternoon, the odds seem to be low.

The Brazos Valley falls inside both Marco and Laura's forecast cone
The Brazos Valley falls inside both Marco and Laura's forecast cone(KBTX)

Marco is expected to strengthen into a hurricane as it moves into the Gulf of Mexico late Saturday. Laura is anticipated to reach hurricane status Monday, after clearing past Puerto Rico, Hispaniola. Marco is anticipated to be a relatively small hurricane while Laura is expected to create a large flow around it.

As of the 10am Saturday forecast from the National Hurricane Center, the paths of these two hurricanes are expected to cross each other. That in itself is extremely rare - particularly in the Gulf of Mexico. Still, Marco is expected to be a Category 1 Hurricane south of Louisiana Monday evening before turning to the west-northwest. Laura is expected to arrive in that same portion of the Gulf, but not until Wednesday - 48 hours later.

If Marco slowed down or Laura was able to speed up, Laura would likely weaken Marco and consume the moisture associated with it.

The Fujiwhara Effect

Have you heard or seen the term Fujiwhara recently?

Named after the scientist who first described the effect. It is defined by the American Meteorological Society as:

Here’s how it would work:

  • Two tropical systems would have to come within 870 miles of each other
  • Each tropical system would need to be of relatively similar strength
  • They start to do a “dance” around a common center
  • If one hurricane is stronger than the other: the smaller would orbit the larger, eventually collide into it and have the associated moisture absorbed.
  • If both hurricanes are of the same size, they could gravitate toward each other before spinning away in different directions
  • In the most unlikely outcome: the two storms would combine to create a larger system

Again, Marco and Laura are not expected to come close enough to each other for this to occur. As far as it is known, mainly in the satellite era, a Fujiwhara has never occurred in the Gulf of Mexico before. Compared to other tropical bodies of water, the Gulf of Mexico is fairly small. It is a feat to have two named storms, much less two hurricanes, at once but unlikely there is enough room for two systems to pull off the effect.

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