Could someone explain High and Low Pressures...

[GulfHills]

and how it effects the path of a hurricane?

[miamiwxgal]

Basically you can think of a hurricane as a cork in a stream with high and low pressure areas steering the hurricane in the atmosphere. Around high pressure the flow is clockwise; currently an area of high pressure is north of Ivan which is causing him to move towards the west (high pressure also acts as a lid of sorts, keeping tropical cyclones from moving poleward which is what they want to do). The question with Ivan is how long will this area of high pressure hang around. If/when it moves away or weakens, it will allow Ivan to move more to the north. Different models have different ideas on when and where this will happen. Hope that helped!

[Dean4Storms]

A very lengthy topic, try going to this link and see if it helps.

http://www.centennialofflight.gov/2003FF/pressure/

[GulfHills]

Thank you! Helped a bunch.

[MWatkins]

The best way I could comprehend this long ago...was to think of a topographical map. You have ridges (mountians of air) and troughs (valleys of air).

If you have a large 3D topographical map...and you roll a marble onto it...the marble is going to roll away from the hills and end up rolling to the valleys.

Now...instead of our map with hills and valleys...think of the hurricane on the same type of grid.

MW

[JayPSU]

Basically you can think of a hurricane as a cork in a stream with high and low pressure areas steering the hurricane in the atmosphere. Around high pressure the flow is clockwise; currently an area of high pressure is north of Ivan which is causing him to move towards the west (high pressure also acts as a lid of sorts, keeping tropical cyclones from moving poleward which is what they want to do). The question with Ivan is how long will this area of high pressure hang around. If/when it moves away or weakens, it will allow Ivan to move more to the north. Different models have different ideas on when and where this will happen. Hope that helped!

I do not mean to disagree with a professional, and I hesitate doing so, but here I know for sure that my old professors at PSU would disagree with one thing you said here. You should not look at a hurricane as a cork in a stream as a hurricane is not a solid entity like a cork is. Perhaps a water balloon or maybe a wad of jello, but not a cork. That's why it's so hard forecasting these things. We're dealing with fluids in rivers of airflow, no real solid entities.

[opera ghost]

Wow- thank you miamiwxgal & MWatkins... really helped.

[miamiwxgal]

JayPSU...

I did not mean to suggest that a hurricane is a solid mass. It's just an illustration meant to help understand this concept, which can be difficult, especially if you don't have a background in fluid dynamics.

Respectfully, Miamiwxgal

[greeng13]

just out of curiosity why do they tend to go polewards.....is it because of the rotation...magnetic pull?

[miamiwxgal]

It is due to the rotation of the earth.

[greeng13]

It is due to the rotation of the earth.

like a centrifugal force that pulls them?

[Wthrman13]

The tendency for TC's to drift poleward even in the absence of any clear steering flow in that direction is due to the beta effect. The beta effect is due to the increase in the Coriolis force as one moves from the equator towards the poles. While the Coriolis force itself is weakest near the equator, the gradient of the Coriolis force (the rate of increase with increasing latitude) is greatest near the equator. Without getting into too much detail, it turns out that a nonlinear interaction between the TC vortex and the environmental N-S gradient of the Coriolis force causes a preferential drift towards the north and west, which is superimposed on whatever other processes are at work that happen to be affecting the TC motion (i.e. steering flow around troughs and ridges, other nonlinear interactions, etc.). A nonlinear interaction in this context is one in which the TC actually changes the environmental flow, and vice versa, rather than considering the TC and environment to be separate (which of course they aren't).

[greeng13]

ok...alot more complex than i thought...thanks

[GABE]

From what I have picked up on this forum, it would appear that low pressure is bad, and higher pressure is good. Being clueless about all of this, the above explanations were quite satisfying....thanks all..........

[cvalkan4]

This is a great thread -- thanks to all of you for the education!

I am hearing that there are (at least) two aspects to this:

1. The hurricane tends to be steered by the winds that rotate clockwise around a high, and counterclockwise around a low.
2. The hurricane tends to go towards a low pressure (trough) and away from a high pressure (ridge).

Thus, a ULL to the west of the storm will (1) push the storm northerly due to the winds rotating around the low, but also (2) tend to draw the storm toward the low, adding a west component to the motion.

And a ridge north of the storm will (1) push it to the west due to the wind rotation around the high, and also (2) repel the storm (pushing it south or at least preventing Beta effect northerly motion of the storm).

Is this a decent way to look at it, or am I confusing or oversimplifying the forces that are involved? Is it possible to know which of these aspects will be dominant in steering a storm in a particular situation? What if there is a ULL to the southwest of a storm -- will the rotating wind push the storm toward the northwest, or will the low draw the storm toward the southwest instead?

[GABE]

O.K. now that one really got me confused.........actually, I can miter the corners of bedsheets pretty darned well........................

[MBryant]

The tendency for TC's to drift poleward even in the absence of any clear steering flow in that direction is due to the beta effect. The beta effect is due to the increase in the Coriolis force as one moves from the equator towards the poles. While the Coriolis force itself is weakest near the equator, the gradient of the Coriolis force (the rate of increase with increasing latitude) is greatest near the equator. Without getting into too much detail, it turns out that a nonlinear interaction between the TC vortex and the environmental N-S gradient of the Coriolis force causes a preferential drift towards the north and west, which is superimposed on whatever other processes are at work that happen to be affecting the TC motion (i.e. steering flow around troughs and ridges, other nonlinear interactions, etc.). A nonlinear interaction in this context is one in which the TC actually changes the environmental flow, and vice versa, rather than considering the TC and environment to be separate (which of course they aren't).

Is this based on theory or is there a measurable test that supports this pull? I suspect that the effect diminishes somewhat at the equator and would like to know if someone has tested the hypothesis closely near the equator.

[GABE]

.............tried to draw pictures of cvalcan's post above. I'm done...............................I'll just have to content myself with the guidance of all of you pro's......
all the best...........gabe

[MWatkins]

It is due to the rotation of the earth.

like a centrifugal force that pulls them?

Kind of...snice the earth is always spinning that has to be accounted for in surface motion. Think facing someone on a merry-go-round and throwing them a ball...even though it appears straight to you the motion actually bends if you observe it from above.

Not sure if this helps or makes things more confusing.

MW

[greeng13]

no...that helped...thanks MWatkins