Since we’re currently in hurricane season, it seems a good time to talk about hurricanes and cyclones. These types of weather systems don’t often find themselves in a traffic jam in Earth’s vast oceans, but when they do, there are consequences.
When two storms move too close together, they start to
influence one another’s strength and track. This tropical tango is known as the
Fujiwhara effect. That scenario played out this week when Hurricanes Imelda and
Humberto danced together off the southeastern US coast.
After devastating the coast of North Carolina, Humberto
moved out to sea, but as it did so, it tugged Imelda to go with it.
On Tuesday (9/30), they were both Category 1 hurricanes and
they were within 467 miles of each other, which is the closest that two
Atlantic hurricanes have come to each other in at least the past 60 years. Two
hurricanes churning side-by-side is more common in the Pacific Ocean but rarely
happens in the Atlantic.
The interactions during these events can vary greatly,
which can make forecasting the tracks and intensity a challenge. Imelda’s track
forecast changed dramatically after she was pulled away from the US and toward
Bermuda.
Both hurricanes struggled in the face of the other’s wind
shear, with Humberto weakening and finally dissipating Wednesday morning. After
that, forecasters expect Imelda to hit Bermuda on Thursday as a Category 2.
In 1921, Japanese meteorologist Sakuhei Fujiwhara published
a paper that said two storms spinning near each other could start rotating
together around a common center point. He was right.
How close the storms need to be to trigger the Fujiwhara
effect is dependent on the size of each storm. If two large storms—those that
span hundreds of miles—get within about 850 miles of each other, they start to
dance. The distance shrinks to 350 miles for smaller storms.
Closely matched storms will orbit around a common point but
then go their separate ways. The circling tugs each storm off the path they
would have taken. In 2017, Hilary and Irwin had this experience in the east
Pacific. They were well matched. Both systems interacted for so long, they
eventually dissipated around the same time.
But if one storm is much stronger than the other, the
stronger one could consume the weaker one. In the west Pacific in 2022, the
powerful typhoon Hinnamnor was headed for Taiwan before it met a tropical
depression that was trying to grow. Hinnamnor and the depression rotated until
the typhoon devoured the depression. Hinnamnor slowed and weakened for a bit,
but when it restrengthened, it took a nearly 90-degree turn from its original
track.
In a rare Fujiwhara scenario, two weak storms spinning
together could merge and create a larger storm,
All of these potential interactions and outcomes pose an
incredible forecasting challenge, even for computers. Any small changes in the
strength or size of each storm, or slight deviation from the anticipated track
throws a model’s complex calculations into chaos.
https://www.nola.com/news/hurricane/hurricanes-humberto-imelda-fujiwhara/article_14cec9cf-1c86-422c-983d-71b320682d2b.html
https://www.msn.com/en-us/weather/topstories/here-s-what-can-happen-when-two-hurricanes-get-too-close-together/ar-AA1NiXg4?ocid=hpmsn&cvid=68d5abc4f3d04d0b915ca4e4134e1350&ei=63
