ATL: FLORENCE - Post-Tropical - Discussion

[ScottNAtlanta]

Still moving at 16mph

[LarryWx]

If Flo weakens faster than projected, what are the implications, if any, regarding future track? Does anyone have a feel for whether or not the steering would change much over the next few days vs model projections? Is projected steering similar at various levels?

By the way, to me she still is quite a strong storm!

[ronyan]

I think there must be shear affecting Florence, upwelling is not happening right now with a forward speed of 16 mph.

There certainly was yesterday! The anti-cyclone causing southwesterly shear and weakening the southwestern quad of the cyclone as it forced dry air into the eyewall. Shear appears to be less today based on the shape of the outflow, but dry air is still messing with the southwestern quad. This will continue to effect the system as it moves towards the coast so the chances of cat4 landfall is very low to very unlikely. If this moves southwestward offshore as some models have shown don't be surprised if it isn't even a major landfall. Some of the models show this as some of them weaken it quite a bit as it moves southwestward down the coast as the system would be sucking up dry air from inland. If it heads more westward = much better chance at a cat3 landfall.

Sure, but there was never a realistic chance of a cat 4 landfall under the "stall near the coast" scenario.

[Vdogg]

Seems to be missing the next forecast point to the east..

This storm has been north and east of the forecast track all day. When will models start taking this into account? The NHC discussion will be interesting...

[funster]

Water reportedly rising already in Oriental NC (near New Bern)
https://twitter.com/hurricanetrack/stat ... 8002906112

Outermost bands getting closer to the coast
https://weather.cod.edu/satrad/exper/?p ... =undefined

[ScottNAtlanta]

Anyone know how many ACE points Florence has generated thus far?

[hurricaneCW]

Models show her getting a boost from the gulf stream tomorrow before finally weakening gradually near LF.

She isn't just going to collapse and there's no upwelling going on. Shear isn't very strong, dry air is minimal due to zero incoming troughs, OHC is going to increase.

Hurricanes above 30N operate differently than those further south.

[cycloneye]

BULLETIN
Hurricane Florence Advisory Number 54
NWS National Hurricane Center Miami FL AL062018
500 PM EDT Wed Sep 12 2018

...FLORENCE MOVING STEADILY TOWARD THE CAROLINA COASTAL AREAS...
...LIFE-THREATENING STORM SURGE AND RAINFALL EXPECTED...


SUMMARY OF 500 PM EDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...30.9N 72.5W
ABOUT 385 MI...615 KM SE OF WILMINGTON NORTH CAROLINA
ABOUT 420 MI...675 KM ESE OF MYRTLE BEACH SOUTH CAROLINA
MAXIMUM SUSTAINED WINDS...120 MPH...195 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...949 MB...28.03 INCHES


Hurricane Florence Discussion Number 54
NWS National Hurricane Center Miami FL AL062018
500 PM EDT Wed Sep 12 2018

Data from an Air Force Reserve hurricane hunter aircraft along with
satellite imagery and various intensity estimates indicate that
Florence has weakened instead of strengthening. However, while the
hurricane hasn't strengthened in terms of peak winds, the inner-core
and outer wind fields have continued to expand, resulting in an
increase the cyclone's total energy, which will create a significant
storm surge event. The upper-level outflow remains impressive and is
still expanding except toward the south.

Florence is moving toward the northwest or 315/14 kt. The new 12Z
global and regional model runs have come into much better agreement
on Florence moving steadily northwestward around a strong ridge
located between Bermuda and the U.S. mid-Atlantic region for the
next 48 hours or so. By late on day 2, Florence is forecast to
approach the southern portion of the North Carolina coast, then slow
down considerably and turn westward within collapsing steering flow,
with a very slow westward motion near the coasts of North and South
Carolina continuing into Friday and Saturday. Corrected-consensus
models HCCA and FSSE remain very close to each other and are quite
similar to the simple consensus model TVCA. Therefore, only a slight
eastward shift was needed to the previous forecast track through 36
hours or so, mainly due to the more eastward initial position based
on the reconnaissance fixes. At 48 hours and beyond, no significant
changes were required to the previous advisory track, which still
shows Florence moving slowly westward across South Carolina and
western North Carolina on day 4, followed by a slow northward motion
up the Appalachian mountain chain on day 5.

A narrow window of opportunity remains during the next 24 hours or
so for Florence to strengthen a little when the hurricane passes
over the warmer SSTs and deeper warm water/higher upper-ocean heat
content associated with the Gulf Stream, and low vertical shear
conditions of 5-10 kt will aid in any strengthening process.
However, significant strengthening is not anticipated due to
Florence's large and expanding inner-core wind field. By 36 h
and beyond, decreasing ocean heat content along with the slowing
forward speed of Florence will likely produce cold upwelling beneath
the hurricane, inducing a gradual weakening trend. When Florence
moves over the shallow coastal shelf waters in 48-72 h, land
interaction and more significant upwelling are anticipated, which
should further enhance the weakening process. The NHC intensity
forecast remains near the higher statistical guidance through 48
hours, then follows the trend of the decay SHIPS model after that
time.

Although the maximum winds are expected to weaken a little more,
Florence is still expected to remain a dangerous major hurricane as
it approaches the coast. The threat to life from storm surge and
rainfall will not diminish, and these impacts will cover a large
area regardless of exactly where the center of Florence moves.

Key Messages:

1. A life-threatening storm surge is now highly likely along
portions of the coastlines of South Carolina and North Carolina, and
a Storm Surge Warning is in effect for a portion of this area. All
interests in these areas should complete preparations and follow any
advice given by local officials.

2. Life-threatening, catastrophic flash flooding and prolonged
significant river flooding are likely over portions of the Carolinas
and the southern and central Appalachians late this week into early
next week, as Florence is expected to slow down as it approaches the
coast and moves inland.

3. Damaging hurricane-force winds are likely along portions of the
coasts of South Carolina and North Carolina, and a Hurricane Warning
is in effect. Strong winds could also spread inland into portions
of the Carolinas.

4. Large swells affecting Bermuda, portions of the U.S. East
Coast, and the northwestern and central Bahamas will continue this
week, resulting in life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT 12/2100Z 30.9N 72.5W 105 KT 120 MPH
12H 13/0600Z 32.1N 74.1W 110 KT 125 MPH
24H 13/1800Z 33.4N 75.9W 110 KT 125 MPH
36H 14/0600Z 33.9N 77.1W 105 KT 120 MPH
48H 14/1800Z 34.0N 77.9W 100 KT 115 MPH...NEAR THE COAST
72H 15/1800Z 33.6N 79.2W 70 KT 80 MPH...NEAR THE COAST
96H 16/1800Z 34.0N 81.7W 30 KT 35 MPH...INLAND
120H 17/1800Z 35.6N 83.4W 20 KT 25 MPH...POST-TROP/INLAND

$$
Forecaster Stewart

[1900hurricane]

Anyone know how many ACE points Florence has generated thus far?

30.4925 units.

[supercane4867]

Saved images of 4 simultaneous named storms in the Atlantic. Perhaps soon to be 5

[ConvergenceZone]

Remember folks, even though the wind speeds have been slowly dropping, and even if it were to landfall as low as a Cat 1, lots of flooding will still be expected. So evacuations should still be taken seriously. It’s still going to be bad! So take it seriously

[jdjaguar]

Saved images of 4 simultaneous named storms in the Atlantic. Perhaps soon to be

One for the books

[AxaltaRacing24]

Saved images of 4 simultaneous named storms in the Atlantic. Perhaps soon to be

One for the books

This is likely at least 1/3 of this seasons activity right in front of us. Incredible September so far, and it’s only the 12th.

[edu2703]

[Hurricane Andrew]

That is a good size windfield...

[Chris90]

I think it is important to remember, especially for storms like Florence, that when discussing weakening or strengthening, it's very subjective. The Saffir-Simpson scale is great for classifying storms in terms of the surface winds they're producing, but that's it. Hurricane impacts have a far greater range than that. So yes, you can look at it and say "great, her winds are coming down, she's weakening!", but an argument can also be made that she's strengthening based off the fact they mention in the latest discussion her wind field has expanded and she's got greater total energy output now, increasing the surge risk. Ike comes to mind. He didn't need major hurricane winds to make a devastating impact.
I just hope people at risk don't become complacent, a decrease in sustained winds does not mean the impact potential comes down too.

[MGC]

I just hope the folks where Florence makes landfall are not lulled into complacency with the recent weakening trend. I was foolish to think with Katrina dropping a category would lessen the damage....wrong. MGC

[Nimbus]

5 PM NHC update got all the 36 hour and 48 hour watches and warnings out.

Ocracoke island is expecting 4-6 ft surge with waves and 4 ft is about the highest ground on the island except for stilt homes. Hurricane force winds out to 70 miles.

[Ken711]

Saved images of 4 simultaneous named storms in the Atlantic. Perhaps soon to be 5

https://i.imgur.com/WUBzxNV.jpg

https://i.imgur.com/VFpoURs.jpg

https://i.imgur.com/5tuQIcw.png

A difference a few weeks make. The lid came off the before relatively quiet storm season in a hurry.

[Rail Dawg]

Been chasing these things for 30 years.

These engines can quickly ramp up unexpectedly.

Tomorrow morning we could see Florence back up to a Cat 4.

Look at the forecast fluctuations just in the past 24 hours.