Major Hurricane Florence: STORM MODE THREAD

[hlcater]

The EPS is a good bit to the left of the OFCL track. EPS consensus still brings it into the NC/SC border area 

[jpeters3]

I suspect there might have been a slight uptick in southerly or southeasterly shear over the past 12 hours.  There was a bit of an increase (to roughly 15 kt) in shear in the CIRA area averaged product:
 

Also not the cloud tops to the southeast of the system that are being blown toward the core, rather than parallel to or away from the core, and outflow is a bit restricted on the southern and southeaster quadrant.

[winterymix]

History and progged probability of hurricane force winds.

https://www.nhc.noaa.gov/archive/2018/FLORENCE_graphics.php?product=wind_probs_64_F120

[yoda]

BULLETIN
Hurricane Florence Advisory Number  49
NWS National Hurricane Center Miami FL       AL062018
1100 AM AST Tue Sep 11 2018

...FLORENCE EXPECTED TO RESTRENGTHEN LATER TODAY...
...LIFE-THREATENING STORM SURGE POSSIBLE ALONG THE COASTS OF NORTH
AND SOUTH CAROLINA...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...26.7N 65.3W
ABOUT 390 MI...625 KM S OF BERMUDA
ABOUT 905 MI...1455 KM ESE OF CAPE FEAR NORTH CAROLINA
MAXIMUM SUSTAINED WINDS...130 MPH...215 KM/H
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...950 MB...28.06 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

None.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Storm Surge Watch is in effect for...
* Edisto Beach South Carolina to the North Carolina-Virginia border
* Albemarle and Pamlico Sounds, including the Neuse and Pamlico
Rivers

A Hurricane Watch is in effect for...
* Edisto Beach South Carolina to the North Carolina-Virginia border
* Albemarle and Pamlico Sounds

Interests elsewhere in the southeastern and mid-Atlantic states
should monitor the progress of Florence.  Additional watches may be
required later today.

A Storm Surge Watch means there is a possibility of life-
threatening inundation, from rising water moving inland from the
coastline, in the indicated locations during the next 48 hours.
For a depiction of areas at risk, please see the National Weather
Service Storm Surge Watch/Warning Graphic, available at
hurricanes.gov.

A Hurricane Watch means that hurricane conditions are possible
within the watch area.  A watch is typically issued 48 hours
before the anticipated first occurrence of tropical-storm-force
winds, conditions that make outside preparations difficult or
dangerous.

For storm information specific to your area, including possible
inland watches and warnings, please monitor products issued by your
local National Weather Service forecast office.


DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the center of Hurricane Florence was
located near latitude 26.7 North, longitude 65.3 West. Florence
is moving toward the west-northwest near 16 mph (26 km/h). A west-
northwestward to northwestward motion with a slight increase in
forward speed are expected during the next couple of days.  On
the forecast track, the center of Florence will move over the
southwestern Atlantic Ocean between Bermuda and the Bahamas through
Wednesday, and approach the coast of North Carolina or South
Carolina in the hurricane watch area Thursday and Friday.

Maximum sustained winds are near 130 mph (215 km/h) with higher
gusts.  Florence is a category 4 hurricane on the Saffir-Simpson
Hurricane Wind Scale.  Florence is expected to begin re-
strengthening later today and continue a slow strengthening trend
for the next day or so.  While some weakening is expected on
Thursday, Florence is expected to be an extremely dangerous major
hurricane through landfall.

Hurricane-force winds extend outward up to 40 miles (65 km) from the
center and tropical-storm-force winds extend outward up to 150 miles
(240 km).

The estimated minimum central pressure is 950 mb (28.06 inches).


HAZARDS AFFECTING LAND
----------------------
STORM SURGE:  The combination of a dangerous storm surge and the
tide will cause normally dry areas near the coast to be flooded by
rising waters moving inland from the shoreline.  The water has the
potential to reach the following heights above ground if peak surge
occurs at the time of high tide...

Edisto Beach to Murrells Inlet...2-4 ft
Murrells Inlet to Cape Fear...4-6 ft
Cape Fear to Cape Lookout including The Neuse and Pamlico
River...6-12 ft
Cape Lookout to Ocracoke Inlet...5-8 ft
Ocracoke Inlet to North Carolina/Virginia Border...3-5 ft

The deepest water will occur along the immediate coast in areas of
onshore winds, where the surge will be accompanied by large and
destructive waves.  Surge-related flooding depends on the relative
timing of the surge and the tidal cycle, and can vary greatly over
short distances.  For information specific to your area, please see
products issued by your local National Weather Service forecast
office.

RAINFALL: Florence is expected to produce total rainfall
accumulations of 15 to 20 inches with isolated maximum amounts to 30
inches near the storm's track over portions of the Carolinas and
Mid-Atlantic States from late this week into early next week. This
rainfall could produce catastrophic flash flooding and significant
river flooding.

WIND:  Hurricane conditions are possible within the watch area by
late Thursday or Thursday night, with tropical storm conditions
possible by Thursday morning.

SURF:  Swells generated by Florence are affecting Bermuda and
portions of the U.S. East Coast.  These swells are likely to cause
life-threatening surf and rip current conditions.  Please consult
products from your local weather office.


NEXT ADVISORY
-------------
Next intermediate advisory at 200 PM AST.
Next complete advisory at 500 PM AST.

$$
Forecaster Stewart

[NJwx85]

Recon appears to have turned around and his headed back towards the storm. Perhaps it was sampling the air ahead of the track.

[olafminesaw]

The visible loop shows the eye just about cleared out apart from some Cirrus.

[csnavywx]

We're dangerously close to this thing not quite making it onshore on the last few runs. This weakening trend of the WAR is bad news. This also has implications for the track forecast since a stronger/offshore vortex will not be pushed by just the weak lower level southeasterlies and will have a propensity to stay offshore due to weak southerlies or southwesterlies aloft. The individual EPS members show just that and a decent minority now don't have landfall for several days, hovering offshore instead.

Also a minor note since I brought up the EPS -- it's still displaying a small left of track bias. This morning's position is again on the right edge of the envelope. It's a relatively small track error and may not end up mattering, but given the situation later on, it might make a difference to landfall times, since the right side of the envelope is favoring closer to Morehead City, NC and a longer stall/loop.

[yoda]

Hurricane Florence Discussion Number  49
NWS National Hurricane Center Miami FL       AL062018
1100 AM AST Tue Sep 11 2018

Data from satellites and an Air Force Reserve reconnaissance
aircraft mission indicate that Florence has completed an overnight
eyewall replacement cycle (ERC). The recon data indicate that the
eye has now expanded to a diameter of 30-32 n mi, and this was
confirmed by an 1103Z SSMI/S microwave satellite image. The aircraft
provided various intensity estimates with a peak SFMR surface wind
of 113 kt noted in the northwest quadrant, a peak 700-mb
flight-level wind of 143 kt in the northeast quadrant, and a central
pressure of 950 mb. The 143-kt flight-level wind would normally
correlate to an equivalent surface wind of about 129 kt. However,
coincident SFMR surface winds were only 108 kt, indicating that the
weak convection that region of the hurricane was not vigorous enough
to bring down the strongest winds to the surface. The 950-mb central
pressures corespondents to about 113 kt. Based on a blend of all
these data, the initial intensity has been set to 115 kt.

The initial motion estimate is now 295/14 kt based on the recent
recon fix data. The broken record continues -- there is no
significant to the previous track forecast or reasoning. Although
the global and regional models continue to make minor shifts
northward and southward, the consensus models have changed little.
GOES-16 high-resolution water vapor imagery indicates that the
amplifying large-scale flow pattern across CONUS is inducing a
downstream ridge over the western Atlantic, with a high pressure
cell centered northwest of Bermuda. This blocking ridge pattern is
expected to keep Florence moving west-northwestward to northwest at
around 15 kt for the next 48 hours or so. However, embedded within
the large-scale flow is a weak shortwave trough over the central and
southern Plains that is expected to eject out northeastward and
weaken the ridging across the mid-Atlantic and southeastern U.S.,
causing Florence to slow down significantly in 72 hours as the
powerful hurricane approaches the Carolinas. On days 4 and 5, an
even slower motion or drift to the west and northwest is forecast,
which will exacerbate the heavy rainfall threat. The new NHC
forecast track is just an update of the previous one, and basically
lies the middle of the guidance envelope between the consensus
models TVCA to the north and HCCA and FSSE to the south.

Water vapor imagery indicates that Florence has finally developed
the much anticipated dual outflow pattern, with outflow jets noted
in the northwestern and eastern quadrants. The latter outflow jet is
flowing into an upper-level low, which is acting as an impressive
mass sink near 25N/49W. These two outflow channels are producing
significant deformation stretching across Florence's inner-core,
which should aid in the re-strengthening process. Now that the eye
has become stable with a diameter of about 30 n mi and since
Florence is expected to remain in a low-shear environment of around
5 kt and over above-average SSTs of 29.0-29.5 deg C, slow but steady
strengthening is expected for the next 24-36 hours. By 48 h and
beyond, Florence's slow forward speed, coupled with the large eye
and relatively shallow depth of the warm water should induce some
upwelling beneath the cyclone that will initiate a slow weakening
trend. By 72 hours the vertical wind shear is expected to increase
to near 20 kt from the southwest, which will cause more significant
weakening to occur. However, given the large overall wind field of
Florence along with the large eye, only gradual weakening is
expected. Once Florence moves inland, the slow forward speed of 3-5
kt will result in rapid spin down and weakening of the wind field.
The new official intensity forecast is above of all of the intensity
guidance based on the aforementioned very favorable synoptic outflow
pattern, and to maintain continuity with the previous forecast.

Key Messages:

1. A life-threatening storm surge is likely along portions of the
coastlines of South Carolina, North Carolina, and Virginia, and a
Storm Surge Watch is in effect for a portion of this area. All
interests from South Carolina into the mid-Atlantic region should
ensure they have their hurricane plan in place and follow any advice
given by local officials.

2. Life-threatening, catastrophic flash flooding and significant
river flooding is possible over portions of the Carolinas and
Mid-Atlantic states from 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 Watch
is in effect for a part of this area.  Damaging winds could also
spread well inland into portions of the Carolinas and Virginia.

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

FORECAST POSITIONS AND MAX WINDS

INIT  11/1500Z 26.7N  65.3W  115 KT 130 MPH
 12H  12/0000Z 27.7N  67.6W  120 KT 140 MPH
 24H  12/1200Z 29.4N  70.6W  130 KT 150 MPH
 36H  13/0000Z 31.1N  73.1W  130 KT 150 MPH
 48H  13/1200Z 32.6N  75.2W  120 KT 140 MPH
 72H  14/1200Z 34.2N  77.1W  105 KT 120 MPH
 96H  15/1200Z 35.0N  78.1W   40 KT  45 MPH...INLAND
120H  16/1200Z 35.5N  79.5W   25 KT  30 MPH...INLAND

$$
Forecaster Stewart

[OUGrad05]

I'm a bit concerned that as the storm widens and possibly re-intensifies that these storm surge projections may prove too conservative.  While I don't think over-forecasting is a good idea either, I would think mentioning the possibility of intensification and moving those storm surge amounts higher would be good practice in this situation.  

[NJwx85]

Nevermind, after a quick loop they turned around again

[NJwx85]

2 minutes ago, yoda said:

Hurricane Florence Discussion Number  49
NWS National Hurricane Center Miami FL       AL062018
1100 AM AST Tue Sep 11 2018

Data from satellites and an Air Force Reserve reconnaissance
aircraft mission indicate that Florence has completed an overnight
eyewall replacement cycle (ERC). The recon data indicate that the
eye has now expanded to a diameter of 30-32 n mi, and this was
confirmed by an 1103Z SSMI/S microwave satellite image. The aircraft
provided various intensity estimates with a peak SFMR surface wind
of 113 kt noted in the northwest quadrant, a peak 700-mb
flight-level wind of 143 kt in the northeast quadrant, and a central
pressure of 950 mb. The 143-kt flight-level wind would normally
correlate to an equivalent surface wind of about 129 kt. However,
coincident SFMR surface winds were only 108 kt, indicating that the
weak convection that region of the hurricane was not vigorous enough
to bring down the strongest winds to the surface. The 950-mb central
pressures corespondents to about 113 kt. Based on a blend of all
these data, the initial intensity has been set to 115 kt.

The initial motion estimate is now 295/14 kt based on the recent
recon fix data. The broken record continues -- there is no
significant to the previous track forecast or reasoning. Although
the global and regional models continue to make minor shifts
northward and southward, the consensus models have changed little.
GOES-16 high-resolution water vapor imagery indicates that the
amplifying large-scale flow pattern across CONUS is inducing a
downstream ridge over the western Atlantic, with a high pressure
cell centered northwest of Bermuda. This blocking ridge pattern is
expected to keep Florence moving west-northwestward to northwest at
around 15 kt for the next 48 hours or so. However, embedded within
the large-scale flow is a weak shortwave trough over the central and
southern Plains that is expected to eject out northeastward and
weaken the ridging across the mid-Atlantic and southeastern U.S.,
causing Florence to slow down significantly in 72 hours as the
powerful hurricane approaches the Carolinas. On days 4 and 5, an
even slower motion or drift to the west and northwest is forecast,
which will exacerbate the heavy rainfall threat. The new NHC
forecast track is just an update of the previous one, and basically
lies the middle of the guidance envelope between the consensus
models TVCA to the north and HCCA and FSSE to the south.

Water vapor imagery indicates that Florence has finally developed
the much anticipated dual outflow pattern, with outflow jets noted
in the northwestern and eastern quadrants. The latter outflow jet is
flowing into an upper-level low, which is acting as an impressive
mass sink near 25N/49W. These two outflow channels are producing
significant deformation stretching across Florence's inner-core,
which should aid in the re-strengthening process. Now that the eye
has become stable with a diameter of about 30 n mi and since
Florence is expected to remain in a low-shear environment of around
5 kt and over above-average SSTs of 29.0-29.5 deg C, slow but steady
strengthening is expected for the next 24-36 hours. By 48 h and
beyond, Florence's slow forward speed, coupled with the large eye
and relatively shallow depth of the warm water should induce some
upwelling beneath the cyclone that will initiate a slow weakening
trend. By 72 hours the vertical wind shear is expected to increase
to near 20 kt from the southwest, which will cause more significant
weakening to occur. However, given the large overall wind field of
Florence along with the large eye, only gradual weakening is
expected. Once Florence moves inland, the slow forward speed of 3-5
kt will result in rapid spin down and weakening of the wind field.
The new official intensity forecast is above of all of the intensity
guidance based on the aforementioned very favorable synoptic outflow
pattern, and to maintain continuity with the previous forecast.

Key Messages:

1. A life-threatening storm surge is likely along portions of the
coastlines of South Carolina, North Carolina, and Virginia, and a
Storm Surge Watch is in effect for a portion of this area. All
interests from South Carolina into the mid-Atlantic region should
ensure they have their hurricane plan in place and follow any advice
given by local officials.

2. Life-threatening, catastrophic flash flooding and significant
river flooding is possible over portions of the Carolinas and
Mid-Atlantic states from 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 Watch
is in effect for a part of this area.  Damaging winds could also
spread well inland into portions of the Carolinas and Virginia.

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

FORECAST POSITIONS AND MAX WINDS

INIT  11/1500Z 26.7N  65.3W  115 KT 130 MPH
 12H  12/0000Z 27.7N  67.6W  120 KT 140 MPH
 24H  12/1200Z 29.4N  70.6W  130 KT 150 MPH
 36H  13/0000Z 31.1N  73.1W  130 KT 150 MPH
 48H  13/1200Z 32.6N  75.2W  120 KT 140 MPH
 72H  14/1200Z 34.2N  77.1W  105 KT 120 MPH
 96H  15/1200Z 35.0N  78.1W   40 KT  45 MPH...INLAND
120H  16/1200Z 35.5N  79.5W   25 KT  30 MPH...INLAND

$$
Forecaster Stewart

Where are they seeing Southwesterly shear infringing on the circulation as it approaches landfall? The only thing I have seen is the ULL Southwest of Cuba which should be far enough away to have no impact. Maybe I am missing something.

 

[mappy]

4 minutes ago, OUGrad05 said:

I'm a bit concerned that as the storm widens and possibly re-intensifies that these storm surge projections may prove too conservative.  While I don't think over-forecasting is a good idea either, I would think mentioning the possibility of intensification and moving those storm surge amounts higher would be good practice in this situation.  

I'm not sure how the NHC can be more proactive in its warning for surge/flooding than this:

1. A life-threatening storm surge is likely along portions of the
coastlines of South Carolina, North Carolina, and Virginia, and a
Storm Surge Watch is in effect for a portion of this area. All
interests from South Carolina into the mid-Atlantic region should
ensure they have their hurricane plan in place and follow any advice
given by local officials.

2. Life-threatening, catastrophic flash flooding and significant
river flooding is possible over portions of the Carolinas and
Mid-Atlantic states from late this week into early next week, as
Florence is expected to slow down as it approaches the coast and
moves inland.

[olafminesaw]

Great analysis here (It continues in the comments below the tweet):

https://twitter.com/pppapin/status/1039404118052237312

 

[beanskip]

12z GFS at 30 trending slightly southwest vs. 6z run 

[Radtechwxman]

Even though the ewrc is done now, the eye is so asymmetrical. Not sure if that effects future intensification or not

[Mrwolf1972]

Gfs is running and at 36 seems the tract is shifting south a some.

[beanskip]

Through 42 a pretty decent SW trend, esp this early in the run. 

[DopplerWx]

gfs much further south at 48. sc/nc border looks to be in the crosshairs.  similar to the euro/eps.

[Mrwolf1972]

gfs might be trying to line up more with the euro from last night on this run

[beanskip]

Wow — through 48 at least a 50-75 mile trend southwest vs 6z.

[CoastalWx]

GFS looking like euro now.

[beanskip]

At 54 headed straight for Cape Fear.  

[CoastalWx]

No real surprise.

[mattb65]

8 minutes ago, StormChaser4Life said:

Even though the ewrc is done now, the eye is so asymmetrical. Not sure if that effects future intensification or not

The larger eye is just in the process of clearing out that's why it appears a bit asymmetric. Overall the hurricane currently looks to be strengthening right now with increase in deep convection in the eyewall and expanding convection while the eye is gradually clearing out debris from the former eyewall.

[yoda]

Florence meandering around ILM at 72

[OUGrad05]

2 minutes ago, CoastalWx said:

No real surprise.

Agreed.  The folks in SC and NC need to be ready for this.  I have a couple friends there that aren't taking it seriously enough.  OBX is going to be decimated with flooding/storm surge and in some areas significant wind damage as well.  Inland flooding will also be catastrophic.  The mountainous terrain is going to further complicate the situation as the system stalls.  

[Wmsptwx]

GFS caving to the EURO through 54.

[bdgwx]

I have to be honest. I'm relieved that the GFS is falling more inline with the FV3/ECMWF. I mean given the option of the GFS or FV3 being more right I'd much rather it be the later since that's what NOAA is hanging their hat on for the next generation model.

[beanskip]

Looks like a direct hit to Holden Beach then a move more westerly at 72 toward the SC/NC line. 

[Mrwolf1972]

Major difference in timing and location out to 72 on gfs