So according to this, a “severe” tornado has wind speeds of 158-206 MPH. According to this, Hurricane Rita presently has winds up to 165 MPH. So this massive storm in the gulf is apparently on par with a gargantuan tornado of “severe” strength.
My mind boggles. I’ve never even been near a storm like that, much less a tornado, and have little sense for scale. When one looks at a picture of a hurricane from space, it’s hundreds of miles across. The eye being considerably smaller, maybe only a few or teens of miles across. Obviously, maximum winds are supposed to be found in the vicinity of the eye and wind speed will diminish as radial distance from the eye increases.
So let’s just focus on the “tornado-force” region of the hurricane. How big is that compared to your average tornado, and how is it configured? Are we talking a giant, broad funnel tens of miles across centered on the eye? Is it more like swaths of high wind that rotate around the eye, like blades on a pinwheel? Do you see these winds more in a lobe on one side? I remember reading that winds on the eastward or westard side of hurricanes tend to differ in strength. I guess I just can’t fathom something so monstrous and powerful and big, and I’m having a really hard time finding anything to compare it too. The only weather phenomenon that seems to come close is a tornado, but that sort of vortex may so differ from a hurricane as to strain comparison. Can someone help me out with some relative metrics, here?
Thanks, and here’s keeping my fingers crossed for the folks in the Gulf, who’ve been through too much already.
I couldn’t find anthing definitive about exactly where in a hurricane the fastest winds occur, but, this article implies it isn’t fixed. Its influenced by topography.
Not much, but a start.
My understanding is that a hurricane has warm air rising from the eye in the center. Surface air is drawn towards the eye to fill the void, and as it does so it picks up heat from the water surface. Coriolis force causes it to rotate couterclockwise. All of this tends to work together so that a hurricane becomes a pattern of winds that accelerate as they spiral inwards towards the eye.
The eye is measured in tens of miles across and tends to get smaller as the storm increases in power and defines itself. The first winds that one tends to notice are sustained gusts of twenty MPH or higher with clouds scudding across the sky. Things gradually pick up as the eye approaches and wind direction shifts from blowing at an angle somewhere between towards the eye and around the eye to rotating around the eye. The highest winds form a wall around the eye, but there may be sustained storm force winds 50-100 miles from the eye (I was in Northwest Houston for Alicia, 1983. At landfall, the winds fifty miles west of the eye of this minor hurricane were at 50+ mph and blowing to the southeast.)
Oh, one more thing; hurricanes spawn tornados, and some of the worst damage in hurricanes is caused by the tornados. Of course, the storm tide and sustained high winds do plenty of damage by themselves.
I used to do hurricane damage modelling for a living. One thing to remember is that the wind speeds used for classifying hurricanes are what are called the “sustained” speeds (average over a one minute period). These are lower than the “gust” speeds (measured over ten seconds) - I don’t recall the factor off the top of my head but I think it’s around a 10-20% difference.
The Fujita rating of a tornado (F scale) is measured by looking at damage after the tornado has passed and estimating what winds it would have taken to produce that damage. I’m not sure whether those are gust speeds or sustained speeds so direct comparisons to hurricane winds are a little harder. Estimating winds from damage is not an exact science either.
IIRC very few actual measurements of wind speeds in a tornado have ever been made (they show up and vanish pretty quickly) - unlike a hurricane which lasts for days and gives plenty of time for NOAA to fly their planes into it loaded up with instruments.
Most of the damage from hurricanes is due to water (not that the winds aren’t ferocious, it’s just that the rain and flooding is worse), tornados do their damage via wind-borne debris (houses don’t “explode from pressure differences”, they get destroyed when stuff blows through at 200mph).
They are both rotating winds, it’s just that a tornado is much tighter (hundreds of yards across, whereas hurricanes are much bigger - the eye may be a few tens of miles and the whole storm hundreds of miles across). If you were unlucky enough to get caught in both I don’t think that you’d really notice the difference between a 120mph wind a 150mph wind.
Winds will be strongest on the side of the system that is rotating in the same direction as the storm is moving - for example if the storm rotates clockwise and it’s moving due north, the strongest winds would be on the west side. That’s in the ideal “all other things being equal” world. The winds will be different depending on terrain and other local conditions.
Hope everyone in the way of Rita stays safe. Good luck Texas.
Winds are strongest in one quadrant (usually the northeast) of a hurricane because of the effect of the motion of the storm. Here’s a quote from thisarticle:
When winds of that magnitude hit your neighborhood, the surreal becomes real. Roofs fly off of building like so many Frisbees whirling through the air. Cars and trucks are pushed along, without their wheels turning. The deafening sounds of debris crashing into your house, glass breaking, lumber being ripped from its place, buildings howling as they are transformed into giant musical instruments. Playing in the background you will hear the moaning roar of a nearby freight train locomotive, otherwise known as winds exceeding 150 mph.
Hurricanes and tornados in the norther hem. are anti-cyclones and rotate counter clockwise.
If the trop storm is barrelling north at 15 MPH and the max sust. winds are 150, then the east side of the storm is bringing 165mph winds plus the storm surge.
Also, all this fuss over Cat 5 and Cat 4 is almost criminal by the media. A 10 mph swing can result in storms being ‘downgraded’…but no one’s roof cares if the winds are 160 or 150 mph. Further, if a storm lives as a 5 with 175 mph winds and fluctuates to max sustained winds of 160…IT STILL is bringing the massice surge that it carried as a 5.
Additionally, hurricanes don’t maintain winds of over 165 - 170 mph very long historically. Usually a couple of days at that wind speed is really stretching the duration for a hurricane. It is always safe to predict a distant cat 5 storm will ‘weaken’…or be ‘downgraded’. In 3 days, Rita won’t be a Cat 5…if she was, she’d be one for the books.
Both these terms should be abandoned by the media, because they imply the wrong thing. It is still a weather monster.
As to the eyewall (NOT the eye…the EYEWALL)…that is the wall of death…where all hell breaks loose.
Is it possible for a hurricane to drop a couple of levels just by spreading out, rather than by breaking up on land.
I just wonder if its possible that something like a category 5 hurricane would be smaller but more intense than say a category 3 hurricane, but the category 3 could perhaps cause more widespread damage.
Is there any rating method as regards the amount of energy dissipated in a hurricane ?
I’m by no means an expert, casdave, but I suspect that a hurricane’s intensity is ultimately a function of the surface temperature of the water it travels across. The storm is one big convective current. An increase in water temperature will increase the storm’s intensity, but I don’t know is a storm can be poorly defined (i.e., spread out over a large area, with a big eye) and have a broad, high storm tide and storm winds over a larger area than a higher intensity storm.
The storms seem to lose intensity once they reach the edge of the continental shelf (at least for the Gulf of Mexico), but they don’t really spread out.
In other words, I don’t know either and I’m also waiting for a more informed answer…
The circulation that causes hurricanes is completely different from that which causes tornadoes. Hurricane circulation is caused by the Coriolis effect (which circulates the winds that would otherwise flow straight from high-pressure to low-pressure zones). Tornadoes… well, I don’t know that much about how they’re formed (yet), but I know it’s not the Coriolis force.
BTW, in the N Hemisphere, the term anti-cyclonic actually refers to air that flows out of a high-pressure zone (in a clockwise direction). Hurricanes are cyclones. Clockwise circulation = anti-cyclonic. Counter-clockwise (our hurricanes) = cyclonic.
Also, regarding tornadoes (and I could be wrong here), my impression is that regular old tornadoes are caused by circulation above which causes downbursts. Most tornadoes spawned by hurricanes are caused by friction/wind shear (since winds are slowed by land & structures, while winds aloft are still blowing stongly). So, according to a book I’ve been reading (Hurricane Watch), if you’re in a hurricane “and the winds near the surface are weak, and you look up and clouds are going by fast, you’re in the environment that’s favorable for tornadoes.”
We should to that, the winds of a hurricane reverse direction as the eye passes overhead. This phenomenon isn’t generally noticable in a tornado since it is much smaller.
