Hurricane Irma 2017

Dan Robinson

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Jan 14, 2011
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Yeah - the Keys would be almost suicidal (as would most barrier islands) but man, being in a well-reinforced structure in a cat 4 or 5 would probably be incredible. Keeping yourself out of harm's way is *somewhat* easy if you have a multi-story fortified structure, keeping your vehicle safe and/or being able to get home within a week on your own is another thing. Several chasers lost their vehicles in Katrina's storm surge. Chris Collura barely saved his car by driving it up a pedestrian walkway.

Most standard multi-story hotels aren't up to spec for even a cat 3, but many of the ones right on the coasts are built to much higher specs.
 
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Mar 15, 2004
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Hey all. I got a bit caught up in the hype about the 180+ MPH sustained winds reported by the NOAA aircraft, and half expected most of Anguilla, St. Martin, etc. to suffer EF-4 levels of catastrophic damage. This clearly hasn't happened. What's the typical de-rating for winds over land vs. open ocean? There must be a fairly significant drop-off in ground-level velocities...
Thanks.
 

MClarkson

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Sep 2, 2004
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In addition to open ocean verse land, the storms max strength is for it's right side eyewall, which stayed north of those islands. I doubt those population centers experienced 180mph sustained winds, but some of the damage pics support 180mph gusts in places. Flipped cars, 100% defoliation. There were also damage pics that clearly do not indicate winds of that strength which could have been just a bit south of the eyewall, or shielded by terrain.

Where the eyewall hit directly it looked pretty ferocious.
 
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Jun 28, 2009
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Keep in mind the motion of the storm also affects ground wind speeds. With a westward moving hurricane, you can add the forward speed of the hurricane to the rotational speed of the circulating winds for the northern eyewall. For the southern eyewall, the forward motion of the storm can be subtracted from the circulatory winds in the eyewall, as they are in opposite directions. Combine this with land friction and other factors, this can partly explain why less than category 5 winds (and/or damage) were observed in some areas.
 
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Aug 22, 2015
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I am agreeing with Jeff on this one, a computer and tv is my plans for this one. Also like Dan said I would have a choice between the plains and canes and the plains will take the cake any day.
 
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Jul 5, 2009
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Yeah - the Keys would be almost suicidal (as would most barrier islands) but man, being in a well-reinforced structure in a cat 4 or 5 would probably be incredible. Keeping yourself out of harm's way is *somewhat* easy if you have a multi-story fortified structure, keeping your vehicle safe and/or being able to get home within a week on your own is another thing. Several chasers lost their vehicles in Katrina's storm surge. Chris Collura barely saved his car by driving it up a pedestrian walkway.

Most standard multi-story hotels aren't up to spec for even a cat 3, but many of the ones right on the coasts are built to much higher specs.


Yeah the logistics of hurricane chasing are hard for me to wrap my head around. I'm still confused as to whether a hotel would actually *allow* you to stay if there is a mandatory evacuation.

On top of that, I could imagine getting down to FL and being unable to find gas, groceries, being unable to get around because of traffic, etc. Despite earlier posts here, I can still see law enforcement making you turn around. And then like Dan says above, even IF all went well with the chase, it could take days to fly out of FL to get back home.

Not that I was ever serious about chasing Irma, I am just trying to figure out in my own mind how the logistics work. I understand them in theory, but as a practical matter it seems overwhelming.

It is something on my bucket list. I really want to do it one day. Maybe when I retire and can spare 5-7 days on short notice. But there are just so few opportunities, I mean until this year it had been 12 years since a major hurricane made a US landfall! And it looks like this landfall could occur at night. Miss an opportunity and you could wait years for the next one... As frustrating as severe weather chasing can be, at least you can often try again the next day, or at worst the next year...


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Jul 5, 2009
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This morning's storm surge map shows only one foot of inundation in the FL Keys, how can that be? Yes it's on the "weaker" side of Irma, but there are other areas of the west coast of FL (i.e., southeast of Naples) that show a 9+ surge.c75cf40785eb71a48877b22496b93d3d.jpg


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Dan Robinson

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Jan 14, 2011
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Irma may be unchaseable as a major cane the way things are going. If the west-of-Miami track holds, eyewall could be entirely over the Everglades as it comes inland. Kay Largo and points west of course are out of the question, too dangerous. Given a western track, by the time the eyewall reaches a safe/accessible highway, it will be well inland and weakening.

Best-case scenario from a chasing perspective is if the eastern eyewall moves over southern Miami/Homestead. If it's too far east, the right-front quadrant (strongest winds) will remain offshore. That's a pretty narrow target, high risk of a "bust" in terms of getting into the strongest part of the eyewall (IMO the only reason to chase a hurricane).
 
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Jul 5, 2009
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Best-case scenario from a chasing perspective is if the western eyewall moves over southern Miami/Homestead. If it's too far east, the right-front quadrant (strongest winds) will remain offshore. That's a pretty narrow target, high risk of a "bust" in terms of getting into the strongest part of the eyewall (IMO the only reason to chase a hurricane).

Wouldn't you want the eastern (stronger) eyewall to move over Homestead from a chasing perspective?


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Jul 5, 2009
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I posted about this before and don't want to sound like a broken record but I am hoping somebody can help explain this - the NHC inundation graphic still only shows 1-3 feet of above ground water levels in Key West, how can that be right?? I know Key West has a higher elevation (18') than many FL shore points, but that's got to be just on a relatively small portion of the island...

http://www.nhc.noaa.gov/refresh/graphics_at1+shtml/095407.shtml?inundation#contents


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Dec 8, 2003
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I posted about this before and don't want to sound like a broken record but I am hoping somebody can help explain this - the NHC inundation graphic still only shows 1-3 feet of above ground water levels in Key West, how can that be right?? I know Key West has a higher elevation (18') than many FL shore points, but that's got to be just on a relatively small portion of the island..
I'm going to guess. It would seem to me that surge is enhanced when a substantial area of water is welled up into a confined spot, say, like Lake Pontchartrain. Whereas, Key West being an island, the surge will just sort of swirl right around that island.
 
Jul 5, 2009
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I'm going to guess. It would seem to me that surge is enhanced when a substantial area of water is welled up into a confined spot, say, like Lake Pontchartrain. Whereas, Key West being an island, the surge will just sort of swirl right around that island.

Thanks Bob. That makes some sense. Or even just thinking of the surge going straight over the island to the other side, maybe that keeps it from piling up. But still I would think the water level itself would rise up higher than a foot as the "mound" of water under the eye advances...

I just saw this picture from Hurricane Wilma, which shows water exactly where the Irma flood forecast does - but again it's the 1' depth that seems odd on the NHC product. (Scroll halfway down the page)

https://www.wunderground.com/cat6/irma-pounding-cuba-cat-3-likely-be-cat-3-or-4-florida

On a related note, what enables the water to pile up inland as much as 6 or 9 feet, when theoretically it can just keep flowing inland until it stops at a lower depth? Really difficult to conceptualize...


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Jul 5, 2009
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Yeah - the Keys would be almost suicidal (as would most barrier islands) but man, being in a well-reinforced structure in a cat 4 or 5 would probably be incredible. Keeping yourself out of harm's way is *somewhat* easy if you have a multi-story fortified structure, keeping your vehicle safe and/or being able to get home within a week on your own is another thing. Several chasers lost their vehicles in Katrina's storm surge. Chris Collura barely saved his car by driving it up a pedestrian walkway.

Most standard multi-story hotels aren't up to spec for even a cat 3, but many of the ones right on the coasts are built to much higher specs.

Mike Theiss just interviewed on TWC, he is in Key West in a hotel he describes as concrete, built in 1926, and IIRC about 15 stories. I also learned that Key West has an 18' elevation - so maybe it is possible to chase a hurricane there. Of course, getting back out of there anytime soon might be difficult...


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Dan Robinson

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Theiss, Brewer and Timmer are all at Key West, all experienced enough and sounds like there are a couple places there that offer adequate shelter. I won't lie, I'm jealous! But that's gonna be one heck of an expensive intercept. They're going to have to pay to be airlifted out via helicopter, as Route 1 is not going to exist in many places afterward. Whatever vehicles they used to get out there will probably not be driveable afterward (broken windows and rain-soaked interiors at minimum), even if they are, it will be weeks if not months before they can be retrieved.
 
Jul 5, 2009
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I think there were earlier posts here about how observed winds never seem to come close to the NHC maximum sustained winds. It was speculated that this was because of sparse reporting/observation stations. But TWC is showing just *forecasted gusts* of around 100mph up on the northwestern FL coast. Why is that?

Right this moment at around 6:42EDT the eyewall is only about 15 miles southeast of Key West and the winds there are still only about 40mph (with higher gusts of course).

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Jul 5, 2009
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Another question is, why is the area of the southwestern FL coast below Naples expected to have the worst storm surge? Yes it's a concave coast where water can funnel and pile up. But there is also primarily an offshore wind there. The wind won't turn onshore until the eye has already passed so there won't be that combined impact of onshore wind as the storm itself pushes the water ahead of it...


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May 2, 2010
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I'm seeing pictures on Twitter right now of a reverse or "anti" storm surge of water rushing OUT to sea in Tampa and Naples.... it looks very similar to what happens right before a tsunami hits. Of course the water is going to come back with a vengeance at some point. How often does this happen ahead of a hurricane and how bad an omen is it for the strength of the eventual surge?
 
Jul 5, 2009
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I'm seeing pictures on Twitter right now of a reverse or "anti" storm surge of water rushing OUT to sea in Tampa and Naples.... it looks very similar to what happens right before a tsunami hits. Of course the water is going to come back with a vengeance at some point. How often does this happen ahead of a hurricane and how bad an omen is it for the strength of the eventual surge?

Yeah I wonder if the surge will just bring the water back to where it was, as opposed to exceeding the normal tidal zone... Also the surge was supposed to be the worst when the eye moved north and the wind shifted to onshore - but the southern side of the hurricane looks like it is weakening significantly, and judging from live coverage from Naples it doesn't look like there's much in that southern eyewall...




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Ashwin D

Real life and death, battle royal going on between the GFS and ECMWF over where Irma will end-up. From reading NHC discussions, I believe they are thinking strong high pressure will win out and Irma will keep moving west. The ECMWF has it pounding Key West then moving it into the Gulf a week from this Sunday.

On the other hand, the GFS and most tropical models are currently taking it into the Long Island region during the same time frame. There has been some westward adjustments over the last few GFS runs so it will be interesting when the models jell and emergency management can start planning.

No matter what the outcome, it appears that another major hurricane will impact the US coastline in the next 10-12 days. Oh, and another wave just came off the African coast!
Any thoughts on the Atlantic Nino(or Nina) that is spawning these storms ? How does the state of the Atlantic Nino mode correlate with these storms ? The public only knows and hears about ENSO and the Atlantic mode is hardly discussed and yet here we are two of the most destructive cyclones in history thanks to the current state of the Atlantic ocean(Ocean + Atmosphere)
 
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Jack Sillin

Enthusiast
Sep 10, 2017
6
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0
Yarmouth Maine
Hi everyone! First timer here!
Been watching Irma for days and am SO glad this storm wobbled towards Cuba then wobbled to the east when making landfall. This could have been sooooo much worse! This morning, upper level outflow and dynamics associated with the jet streak to Irma's north (PRE) are now dominating the system as the inner core evaporates approaching Jacksonville. It's amazing to watch! Loop: https://weather.us/satellite/800-w-320-n/top-alert-superhd-15min.html#play
 

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