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» Online Classroom   »   » Public Discussion of Marine Weather   » Hurricane Irene

   
Author Topic: Hurricane Irene
Rich


 - posted August 26, 2011 07:44 AM      Profile for Rich           Edit/Delete Post 
If we have a barometer in the house are we measuring the atmopheric pressure in the house and would it be different if the barometer was outside the house?
Is there any rational to the statement opening the windows a crack will equalize the pressure and possibly prevent windows from breaking?
I'm in New Jersey and we are preparing for the huricane.
Rich

David Burch


 - posted December 20, 2011 11:17 AM      Profile for David Burch           Edit/Delete Post 
sorry to have missed this valuable question. This is one that actually might be best for our public discussion of weather, and i will move it there later. Instructors monitor those daily, but do not monitor the chat rooms very often.

in the meantime, it depends on how tight the house is. generally a home is not pressure tight for slow changes at all... so your barometer indoors is measuring the same as outdoors, especially for a typical barometer that might only shows pressure to the nearest mb.

in our office, for example, we have very poor sealing at the front door, so we just assume in comparisons that indoors = outdoors. But our instruments are very high precision showing pressure to nearest 0.01 mb. with these units we can actually detect gusts going by the front door, or folks opening and closing an office door.

the point about preparing for sudden drops, however, still makes sense it seems. a tornado could create a huge and very sudden drop which normal pressure leakage would not compensate for, so an open window could make a difference i would guess.

a hurricane, though certainly bringing impressive pressure drops, is bringing a relatively slow change compared to pressure equilibrium indoors. I would doubt that an open window would make any difference.

We have typical pressure patterns for hurricanes in the book, along with typical speeds, fast being some 20 kts, though more likely much slower.

From: Starpath, Seattle, WA
David Burch


 - posted December 20, 2011 11:25 AM      Profile for David Burch           Edit/Delete Post 
by the way, in a hurricane condition, i do not think windows get broken so much by a pure pressure change, but rather by the venturi effect of having very strong winds pass by the front of the window, regardless of the actual ambient pressures.

In other words, in a tornado or hurricane, roofs are not blown off of houses, they are sucked off of the houses. In this sense, opening the windows could protect them (in any source of very strong winds), but it would have to be every one that you want to protect. It would also apply to doors, etc. In other words, it is not to minimize the overall pressure differential inside vs outside, but just very locally at that exact surface and it is wind related more than pressure related.

From: Starpath, Seattle, WA
David Burch


 - posted December 20, 2011 11:30 AM      Profile for David Burch           Edit/Delete Post 
This issue is one that we hopefully never have to face at sea, but is nevertheless the same, land or sea.

I believe the transition takes place somewhere around 60+ knots of wind. That is at some 60 or below damage is caused by the force of the wind, with this force being proportional to the wind speed squared.

But once the wind is 80 or more, then there is no protection from it. the damage is caused by pulling objects apart, not pushing them to pieces.

From: Starpath, Seattle, WA


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