Time to start paying attention to Florence?

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8 hours ago, rst3 said:

I'm sure quite a few saw this image today, but it's worth posting again. The inner core of Florence during a period of rapid intensification




Flo leveled off tonight, for several reasons. First of which is an eyewall replacement cycle. After the initial ramp up of a powerful cyclone.. an outer ring of thunderstorms often forms outside the main eyewall.




This chokes off the inflow to the core, and the max windspeed drops somewhat.. typically for say 12 to 18hrs. During this time the inner core dies off completely and the new outer, larger ring takes over as the eyewall. This enlarges both the eye, and the overall windfield. Once the eyewall replacement cycle is complete with a new eyewall, strengthening can begin once again. Most experts are on board with another round of intensification ramping things up again on Tuesday.



> I did want to stress that Florence will likely be the most intense hurricane to hit the 'mid' eastern seaboard in our lifetimes.


Look folks: I've been doing this a long time. It's very, very difficult to bring a Category 4 on shore in the Carolinas. Yes-- they happen out at sea *near* the Carolinas every now and then, but to actually bring that caliber of hurricane on shore? at that latitude?? Well that's exceptionally rare. 


As for my opinion on impact: the immediate coast gets flattened within 50 miles of the eye. Winds in the right front eyewall will gust into the 140s on the coast. As landfall approaches, surge will completely overtake and cover barrier islands to the right of the eye. They will be totally 100% underwater. Reclaimed by the sea.



As bad as this looks for the coast-- and it will be horrendous-- the big wildcard for the storm may actually be inland flooding. Yeah.. the coast and eastern NC will be hit terribly by surge, and extreme winds... but the fact is-- much of the impact area is open rural farmland. Outside the immediate strip of coastal communities? eastern NC is largely barren. It's a wide coastal plain of industrial pig farms and tobacco plantations. 



So after the coast.. Florence is just picking on hogs for a hundred miles. NBD.

But after that? Then comes the risk for catastrophic flooding. *This is definitely not set in stone by any means though*. The models are all over the place with respect to rain totals: Some say 10ish; others up to 30.


10 inches sure is lousy to get.. but 'doable' for those impacted.

25? That is not.


If 15-25 inches falls in the Appalachians of NC and Virginia, it will be biblical. Here's what happened when hurricane camille dumped 8-27" on the region 50 years ago:






Nice work on the hurricane, however there are plenty of small towns in eastern NC.  And tobacco "plantations" went out with the civil war.

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2 hours ago, R.R. Bridge Fisher said:

Thursday looks fishy

I've been wondering about this myself. So, your regular stormy big surf setup has the wind blowing onshore as well.. which sort of helps drive bait schools against the beach imo. But does 4-6ft rollers coming in on a glassy surface with no wind do the same? Anyone think fishing "clean" wavesets from far off storms (vs your typical local storm surf with onshore wind) is different? Or all the same for fishing?

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5 mins ago, Bullred44 said:

Nice work on the hurricane, however there are plenty of small towns in eastern NC.  And tobacco "plantations" went out with the civil war.

Yeah probably could have worded that better. Last time I was down there was for Isabel in 03. Nice people those Carolinians, just not a lot of em in the eastern agricultural counties and small towns I visited during that storm. 

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Just the surf will kick a bite in gear if there is bait and fish in place, but sometimes that wind is needed to get the bait pinned against the shore.  Better results have often come from the wind and surf, vs just the surf

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@Bullred44 geezus, I see you're topsail. Yikes. Stay safe man. Just a terrible thing what's on deck for homes and businesses down there. This ones a killer.


As for what to expect for winds-- here's a post-storm windfield analysis for Hurricane Hugo, just down the coast in SC. Florence will likely hit with a similar profile. So wherever the eye comes ashore, these types of conditions should be expected at roughly the same distances geographically. 


Edited by rst3

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Really good stuff on the weather predictions. This thread is one of the best recently for it.


Only thing I'd quibble over; flooding those low lying nastyazz NC pig farms is definitely a BFD.



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- some good, some bad

- few corrections to prev posts


Quick mea culpa off the top!

Realized prev comments about eastern NC being some "barren, hog-filled wasteland" were, uh, juuuust a little tone deaf \_(ツ)_/ . Apologies to any friends down there whose lives are about to get turned upside down. Can only imagine if I'm 3 days from sitting on my roof with my family, surrounded by floodwaters, and some jackhole from Massachusetts is writing off my entire county as one giant hog pen....


Whoops.:) Hey, we don't get our Masshole reputation for nothing...


2) Corrections

In a prev post I used the windfield of Hugo as a guide on what to expect. Ehhh, bad guide now that I think about it.

The main reason is that Hugo came onshore and accelerated to 35mph: it raced inland quickly before the storm winds had a chance to spin down. In fact, it was into Charlotte only 5 hours after landfall, some 175 miles inland, and still had enough punch left in the tank to gust 100 in that city.


That will not be happening with Florence.


All indications now point to Florence coming on shore very slowly, perhaps moving only 3-5kts-- then effectively stalling.



This means more wind damage for coast, but much much less inland. 


The other thing this means is that by being unable to punch very far inland, the mountainous areas of NC/VA may escape most of the brutal torrent of rain. Which is good for them. But really, really bad for central areas and coast.. because a stalled out system near/on the coast can still tap Atlantic moisture. The resultant freshwater flooding may be catastrophic.



Important to note that while windspeed is the 'sexy' stat that gets all the coverage in the run up to hurricanes, it's really not the big risk with these storms. Water is. 

Surge and flooding do most of the property damage, and kill most of the people


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Forecast Changes pt 2


So it's looking more likely Florence comes crawling into the coast. The reason for this is the developing ridge over the upper midwest now looks to be stronger than initially thought.



It basically prevents Flo from coming north, poleward, like she wants.



This has some implications for the storm itself, and major implications for the flooding impact, like mentioned before. In fact, newest models in show after hitting the coast, the damn thing drifts south into Georgia



Because of the stronger ridge. Florence's approach will be slower. This gives more time for a belt of 20kt windshear to arrive on scene near the coast. 20kts of windshear is not good for storms and is likely to disrupt the core, at least a little, which favors a slight reduction in windspeed at landfall.


And by crawling in at 5kts, Florence will spend a lot longer over the cooler shelf waters, which are set up from the coast.. 50 miles out to the Gulf Stream.


Hurricanes are nothing more than a heat engine. As they get stronger, the giant seas kicked up induce upwelling of colder waters towards the surface. This cools the water and lowers the amount of heat available to power the engine.


Key point though is not all ocean real estate is the same when it comes to temperature: much of the ocean has a fairly shallow surface layer of warm tropical water. Beneath this are colder waters that are easily churned up. So normal areas get cooled off by raging hurricanes; this takes the foot off the gas pedal.


But other areas like warm eddies and the Gulf Stream have warm water that extends down hundreds of feet. Over warm eddies or the Gulf Stream, the gas stays on.



Back in 05 Katrina exploded into a Cat 5 over a warm eddy. Once she came off, immediately dropped back to a 4. And eventually hit the coast as a 3.



Here off NC, the coastal shelf waters extend about 50 miles.




If Florence is crawling through the thin-layer shelf waters at 5kts over like 10hours, that's gotta knock at least a little off her wind speed. Between that mechanism, and the impending 20kts of windshear, I suspect Florence hits the coast as a 3. Even if she was a beast of a 4 ...a half day or 24hours before, only 75 miles off the coast...when the shear was lower and she was over the Gulf Stream 


Little practical difference between Flo hitting at 120 vs 140 though. And a crawling 120 is probably worse than a 140 that races by. Plus, the surge will stack up against the coast through multiple tide cycles for a lot longer. Again, the surge and the rain is the big story here-- not the loud and scary wind


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Welp! More changes by the hour!


EURO ensemble showing tight track til coast [you bet house on this track], then an absolutely huge spread thereafter[you dont bet a sack of stolen nickels on this track]



Major uncertainty as to what happens after the damn thing gets to the NC coast. Might not even cross the coast at all! Could just stall on or just off the NC coast, dump 15-30" of rain, then slowly drift south along the coast all the way to Georgia. 



> Nobody knows what's going on rn


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Despite change in model runs, latest official forecast by the National Hurricane Center still has the post-impact "inland track" up, although they shifted it a little in response to this afternoon's shenanigans.



Generally, they resist large swings in the track if one model run starts to show a seriously different solution. They dont like to get screwed by following whats called the "windshield wiper effect" as things change run to run. But if solutions hold over the next few runs, say 12, 18 hours? Then I expect major shifts south in the official post-impact track to occur.


> again, right now nobody has a firm handle on this thing after initial impact. They've also knocked down the expected strength at landfall from a 4 to a minimal Cat 3/115mph. Same reasons discussed earlier. Just goes to show how incredibly difficult it isto put a cat 4 on shore in NC. Everything can be perfect up until the last 75 miles, then 1 wrench into the storm and it's down to a low 3.

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Oh come on! What an ******* storm



Forecasters are, right now, chugging maalox and popping nitroglycerin pills like candy. Total nightmare of a forecast.


Good news is: this is the American GFS model, which means at least a little grain of salt. Bad news is.. the GFS has been pumped up with extra weather balloon and aircraft data, so in theory it shouldn't be too bad rn. 

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