I’m trying to figure out what effects low-pressure has on the weather. Why does the Weather Channel keep pointing out the low-pressure of Sandy as being such an important thing? Thanks!
the lower pressure makes its size bigger.
Winds are driven by a pressure difference. Lower pressure means stronger potential winds.
Tightly cover a large bowl with saran wrap - that’s the Earth’s atmosphere. Add a few drops of water to the surface - those are clouds or weather systems. Now press your finger down in the middle of the saran wrap - that’s a low pressure system. Watch as all the water runs down into the depression you’re making.
FWIW, Sandy, with pressure at 942mb, is nowhere near a record low pressure. It is a category 1 hurricane. An early estimate of potential damage is $88 billion USD.
Our little island of Grand Cayman experienced Hurricane Ivan back in 2004 on the day it reached its lowest pressure of 910mb. That was the tenth lowest recorded central pressure of a hurricane up to that time. That was a borderline cat 4/5 storm and caused US$1.85 billion (2004 USD, $2.28 billion 2012 USD) of damage just in our 76 sq miles.
Sandy’s pressure is pretty remarkably low for an October-almost November hurricane, and pretty low for almost any hurricane, save the monsters, really. Hurricane Grace, which spawned the “Perfect Storm” back in '91 had a lowest pressure of 980mb according to Wikipedia.
It’s a record for this area. New York City’s record low is 962. DC is 966.5. Philidelphia and Baltimore are in the 960s, too.
Not necessarily. It’s the pressure gradient that’s important. A lower central pressure could mean a stronger pressure gradient, but if the system overall is larger, then the gradient might not be as great as in a smaller system with a higher central pressure.
Let me tell you a little something I learned in Hurricane Andrew: The lower the air pressure, the worse the skull-splitting headache will be. H. Andrew was superlow pressure, lowest recorded in, I dunno, forevers (922 mbar). As the storm passed, I found myself curled up into a tight ball, whining and whimpering because I thought someone had clamped my goddamn head in a vise. It really didn’t matter how many Advil I took. My head stopped hurting when the pressure went back up to something approaching normal.
After that, I pay attention to two things when on Hurricane Watch: wind speeds (anything over 110 mph and I’m getting the hell outta town) and barometric pressure. Anything under 1000 millibars and I’m stocking up on Vicodin before the storm comes. Katrina’s lowest pressure was 902 mbar – I bet that one was a skullcrusher and I’m glad I wasn’t anywhere near it.
Me too on splitting headache, with same therapy, and same results (so far). (Typing and staring at a computer doesn’t help at all, but I’m also a more than usually bored shut-in.)
Don’t many animals respond in noticeable ways to pressure drop?
Also, something about cold air from Canada, unusual at this time, canceling out something or other that causes most hurricanes to dissipate over the Atlantic. I don’t know what that’s about.
But at least I get to Blame Canada.
I get a headache when a big storm blows it, too. Huh - didn’t know it was so common, though my mom and aunts have mentioned it and we all have low blood pressure so I figured that was a factor.
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FWIW, Sandy, with pressure at 942mb, is nowhere near a record low pressure. It is a category 1 hurricane…
I don’t understand this unit. I dutifully checked, but I clearly missed something.
It’s a unit of pressure - mb = millibar. A “standard atmosphere” is 1013.25 mb. Lower pressure usually means precipitation; higher usually means dry conditions.
Here’s a conversion table if you are more familiar with one of the other units of pressure:
A pressure reading of 942 mb is usually stronger than Cat 1 or 2. Usually any storm lower than 950 mb will be at least a cat 3. The reason why this is “only” a cat 1 is that it is so large that the gradient is not as steep as usual with that low a pressure, as Colophon pointed out. As Sandy crosses the warm waters of the Gulf Stream her pressure drops due to added adiabatic processes. The ocean temps near the shore are only 61-62 degs, which should cause Sandy to lose her tropical characteristics (warm core), but there is added energy from two other sources, baroclinical lows approaching. The approaching cold front in the southern US prevented Sandy from turning in there, as usually is the case; however, there is a large blocking high in the northern Atlantic, causing Sandy to turn west, away from the high.
Another issue related to low pressure is the “storm surge”. Storm-related winds can produce flooding by driving water on shore. When the atmospheric pressure is low, the level of the ocean rises a bit and that leads to increased flooding in coastal areas.
Do you also get a headache when driving up a hill? The standard pressure at just 3000’ MSL is around 908 mb, which is worse than a severe hurricane.
I get terrible headaches (and general joint pain) during low pressure weather too. South east England hasn’t had a serious weather incident like that as long as I’ve been living here, but even when it’s just normal seasonal low pressure, I have a clamping headache and it hurts a little to stand and move.
I don’t get these “low air pressure = headache” statements either. How would anyone cope with flying if this were the case? Aircraft are generally pressurized to the equivalent of around 7000’. I don’t see people writhing in the aisles on a normal flight.
This is true. The lowest pressure in a typical winter storm here in the UK is maybe around 960mb. I have a watch with an barometric altimeter, and in aircraft I notice it goes down to around 760mb. At the top of a 3,800-metre mountain in the Alps it was only around 650mb IIRC.
And yet I too sometimes get a headache when a low-pressure system comes in, even though the pressure drop may be only 50mb or less, compared to 250mb over a much shorter time when I go up in a plane. Maybe the more gradual pressure change means there’s no chance for your ears to “pop” and equalise the pressure?
I’ve gotten headaches from low pressure both when flying and when driving in the mountains. I’m not a usual migraine sufferer, but it happens.