Hurricane Rotations

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CPW

23
12
Here's a question I want to ask a physicist:
Is it possible for a hurricane in Earth's northern hemisphere to have sufficient linear momentum (directed South) to cross Earth's equator and still persist as a CCW-rotating hurricance but in the southern hemisphere? If so, for approximately how much time?
 

jim mcnamara

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You are proposing a what-if type question. That means you have to "suspend" parts of observed weather patterns, air currents, some basic Physics (perhaps), and so on. Can you see what has to change in order to get an answer? Other than it does not happen normally. And would it make sense?

See this insight first, then we can maybe help you go forward. (it is short, please do read it):

Hint: Rossby waves
 

CPW

23
12
Thank you for sharing the link to the post about "What If" questions. I read it. I agree my question is somewhat of that type. Perhaps I have watched too many YouTube videos with questions of that type. :smile:

I'm still curious to know if a hurricane, in particular the eye of the storm, can or has ever crossed over Earth's equator.
 

256bits

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I'm still curious to know if a hurricane, in particular the eye of the storm, can or has ever crossed over Earth's equator.
Hurricanes are funny creatures alright, and I think it does take some understanding to figure out how they will behave. Usually around 5 degrees north or south of the equator, the storm cells do not merge to form a hurricane, but after forming, north hemisphere, would it ever travel southwards rather than northwesterly, as they seem to do, is your question I think.

Well here is why I think it is a good question:
Why they do not follow the Hadley cell air currents, which flow south west at the surface, rather than north west, is beyond my comprehension.
And why do they, when they hit the east coast of N.America not continue to travel across the land but have to follow the coast, changing their direction to northeast.
I added a few more things I find funny about them that the weatherman never explains.
I hope you don't think of that as hi-jacking your thread, or question, but I would like to know too.
 
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And why do they, when they hit the east coast of N.America not continue to travel across the land but have to follow the coast, changing their direction to northeast.
I added a few more things I find funny about them that the weatherman never explains.
I hope you don't think of that as hi-jacking your thread, or question, but I would like to know too.
The main influence on the direction of movement of hurricanes is the direction of the wind. In this time of year, the north east trade wind does not blow up to the equator, but op to the Intertropical convergence zone (ITCZ), with will be about 10N in the middle of the atlantic, but about 20N in the caribean. Because the winds follow these, the average wind direction is more east, than northeast.
https://earth.nullschool.net/#current/wind/surface/level/orthographic=-58.07,16.12,1093
The ITCZ can be clearly seen in the atlantic, and the pacific (blue line without any wind), but it gets more confused above the caribbean.
At the end of winter, it would likely be easy for a cyclone to cross the equator, driven by the northeast trade wind, but that's exactly when you get no cyclones at all.
Another effect on the movement of cyclones, is the Beta effect, this comes from the difference in the coriolis force. It will make northern hemisphere cyclones move to the nortwest, and southern hemisphere cyclones go to the southwest.
https://www.wunderground.com/blog/JeffMasters/the-beta-effect.html
This will tend to keep cyclones off the equator as well.
 

tech99

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My understanding is that it is the upper air movement which controls the motion of the storm, and is the reason why Dorain was very slow moving over Bermuda.
 

CPW

23
12
Thank you tech99, willem2, 256bits, and jim mcnamara for your replies. I learned something new about hurricanes.
 

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