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Hurricane Florence Discussion Thread

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Saw some folks asking for a single thread for Florence.  Figured I’d go ahead and make it since I had time on my lunch break.  Thanks to all who have been posting in the winter thread, it’s been a great disco the last few days. 

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From MRX, nothing earth shattering but a reminder of how the area could be affected even before the remnants of Florence arrive in the Valley.

Hydrologic Outlook

Hydrologic Outlook
NCC039-043-TNC001-007-009-011-013-019-025-029-057-059-063-065-067-
073-089-091-093-105-107-115-121-123-129-139-143-145-151-153-155-
163-171-173-179-VAC105-167-169-191-195-520-720-130330-

Hydrologic Outlook
National Weather Service Morristown TN
1122 AM EDT Wed Sep 12 2018 /1022 AM CDT Wed Sep 12 2018/

...Threat of Flooding Due to Hurricane Florence Is Increasing...

The latest forecast track for Hurricane Florence from the
National Hurricane Center shows the storm stalling near the
Carolina coasts on Friday before moving westward through South
Carolina during Sunday. This track has the potential to produce
very heavy rainfall over the mountains of western North Carolina.
Heavy rains in these areas would result in sharp rises along
rivers draining out of western North Carolina into east Tennessee,
such as the French Broad, Pigeon, Hiwassee, Little Tennessee, and
Nolichucky Rivers.

Of course, if the remnants of Florence come to impact east
Tennessee more directly during early next week, then the risk of
locally heavy rainfall will spread into east Tennessee and
southwest Virginia.

Keep informed of the latest information on the track of Hurricane
Florence as this flood threat develops.
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Major changes on the 18z GFS with Florence.  No jog down the coast.  Landfall in southern NC and then it just rams its way to the spine of the Apps.  Good thing for the coast.  Not a great development for the mountains.  It does not lose as much moisture and brings heavy rains all of the way to Boone.  

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In less than a week I've recorded 3.5 inches of rain.  With the Clinch already up to it's banks rain is not something that would be appreciated at the moment. At least for folks around here we have high ground. I can't imagine being surrounded by water on all sides with the nearest land many football fields away like during storm surge and flooding in the tidewater. Of course with that said with elevation comes the risk of landslides. Still, I think we get the better of the deal by far. Anyway regarding Florence I and a bunch of others have been wondering as to why it has appeared so ragged on IR satellite.  Paying attention to the discussions on multiple threads it would seem shear is the most likely cause because the SST's would certainly support at least some marginal re-strengthening from my understanding. I've heard the idea of dry air intrusion passed around too but the source never really seems apparent. Right now the southern half of the storm pales in comparison to the northern side. Of course on the less positive side of things it would seem Florence has traded intensity for an increased wind field.

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It is pretty amazing to see how many of the models struggled w this system, even at one point taking it agains the Gulf Stream current.  Steering mechanisms were were/are weak and this has caused many problems w forecasting the storm.  Overall, still amazing that we can model a hurricane these days.  The storm has spread out according to the main Florence thread.  This has made it next to impossible for the system to restrengthen.  We want it as weak as possible for the folks on the coast.  Still, extended times w winds and multiple high tides is not a good recipe.  Bout "go time" for the coast....

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2 hours ago, Carvers Gap said:

It is pretty amazing to see how many of the models struggled w this system, even at one point taking it agains the Gulf Stream current.  Steering mechanisms were were/are weak and this has caused many problems w forecasting the storm.  Overall, still amazing that we can model a hurricane these days.  The storm has spread out according to the main Florence thread.  This has made it next to impossible for the system to restrengthen.  We want it as weak as possible for the folks on the coast.  Still, extended times w winds and multiple high tides is not a good recipe.  Bout "go time" for the coast....

I with you on your coast comment, it’s not even worth risking it.  Get out while you can and just play it safe.  The power outages are gonna cause serious issues as well, especially with the amount of rain being forecastEd.  Down power lines and standing water do not mix well.  The winds pinning the water inland is not going to help at all either.  Overall, just cause the storm has weakened that does not mean the effects will get better because of that weakening.  That’s a scary thought.

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Jeff Piotrowski, Jeff Gammons and others are already documenting surge coming up on the barrier islands, midday Thursday. Florence still has as much energy as it did before, but the wind field is spread out. Unfortunately the storm surge will be major hurricane material. 

When a figure skater spreads out, spin slows down; but, they have the same momentum and energy as before. I'm afraid what we trade in for less wind damage will net out worse with storm surge damage. Inland flooding has not changed, devastating.

While I appreciate their documenting it, this Jeff ain't chasin' any 'canes! My tornado drought would have to go on a couple more years to impact my judgement that way, lol!

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I've been wondering too, if the center can track just right, if the downsloping might be offset by a perfect trajectory out of the NE, down the valley.  It would still be an overall downslope flow, but the plateau and Smokies funneling that flow could force it to narrow and change speed and maybe create some lift that way. Not saying anything even approaching what places east of Blue Ridge will see, but might offset the overall downslope if the flow gets just right. 

I've noticed that sometimes as snowstorms are heading up the coast, that precip. can hang around in the central, great eastern valley and areas NE, longer than it seems like it should and have wondered why this might be. A Met. in the bigger Flo thread mentioned frictional convergence this AM and while this is not the same process at all, it got me thinking about how the valley/ mountains might impact flow/ speed/ trajectory and shape meso/ microscale convergence or divergence. An example: South of where the Crab Orchard Mountains/ Frozen Head bulge out from the Cumberland Plateau, the angle of the plateau's edge in respect to the valley then plunges slightly more S than the edge of the Smokies, and maybe this forces some of the air a little eastward, pushing it into the rest of the flow still heading more SW down the valley.   (Image 1)

None of this may apply at all here, since the overall motion of the storm looks to be WNW changing to N with time, as opposed to the usual SW to NE, but will definitely be trying to watch radar to look for any of the above.  

On the satellite today I did notice something along these lines, at least with clouds: (Image 2) Although it looks like it invalidates my reading of the southern valley in aiding convergence.  Maybe the flow is more across the mountains in the southern, eastern valley (thus more downsloping) with a NE flow and the more subtle processes can only aid lift further north where the downsloping is less, since the flow isn't directly across the Smokies, but roughly down I-81? 

2018-09-14_16-50-01.jpg

2018-09-14_16-46-46.jpg

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From the MRX disco this morning......

SHORT TERM...(Today and Tonight)... Tropical storm Florence will move slowly toward the southern Appalachians through tonight. Bands of showers and possibly a thunderstorm will affect the area this afternoon with greater coverage for tonight. Periods of moderate to possibly heavy rains is expected, but downslope easterly winds will limit rainfall amounts from this system. Besides the rain, tightening pressure gradients from the remnants of Florence will also produce windy conditions, especially over the higher terrain. The strongest 850mb winds will be from the Smoky Mountains northward into southwest Virginia. Have issued a wind advisory for these areas. Breezy conditions are likely across the valley as well.

LONG TERM (Sunday through Friday)...By Sunday...the remnants of Florence will be moving through the Southern Appalachian Region. This system will bring widespread rain and increased winds. Precipitation totals should be diminish somewhat by downsloping effects which will limit the rainfall. On average...less than an inch is expected over southern areas and 1 to 3 inches are possible across the rest of the MRX CWA. Locally higher amounts are expected but overall...believe the potential for widespread flooding or flashing flooding will be minimal. Main concern continues to be the potential for high river levels...especially for those rivers with headwaters located in the Carolinas where heavier rainfall is forecast. Also of concern will be increased winds...especially over higher elevations. A wind advisory will remain in effect over portions of the East TN mountains and southwestern VA. Gusts near 40 MPH will be possible in these locations.

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MRX and WPC raised QPF a bit on the Upper Plateau. Looks like with Florence tracking nearby/east, vs west of the Plateau, the south side of Florence can indeed get a chance to flip winds around from the northwest on Monday. The said QPF is a little delayed compared to the Smoky Mtns, not just waiting on the low press. but also the wind shift.

Saturday skies were so beautiful deep blue like we rarely see. We actually had some nice blue days the last week, but Saturday was a true gem.

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Wind didn't seem high enough to rip the leaves. Also lucky it did not happen a couple weeks later. Anybody reports from elevation?

Valley was a snoozer, but some nice sunrises and sunsets!

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Somehow, even with a tropical depression, NE TN was dry slotted.  Winds were just breezy here, and barely that.  The best side effect is that it is cool when the sun is not out.  Really feel for the folks along the coast who will be dealing with this for quite some time.  The rainfall amounts along the coast and just inland were incredible. 

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It has to come from the southwest rule appears to be true no matter what kind of low press. Winter storm, spring severe, mid-latitude, cold core, warm core, tropical... from Mars, well just kidding about that one!

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