ATL: FLORENCE - Post-Tropical - Discussion

[TheDreamTraveler]

Hurricane Florence Discussion Number 30
NWS National Hurricane Center Miami FL AL062018
500 PM AST Thu Sep 06 2018

Vertical shear has taken its toll on Florence today as evidenced by
a continued degradation of the overall cloud pattern. The
circulation appears tilted, with the low-level center partially
exposed to the southwest of the deep convection. Subjective and
objective Dvorak Current Intensity (CI) numbers have fallen, and a
blend of the various estimates supports an initial intensity of 70
kt.

The intensity forecast is relatively straightforward in the
short-term as shear is expected to remain strong, which should
continue Florence's weakening trend, potentially taking the system
below hurricane strength. By 24 hours, vertical shear is forecast
to decrease, and the SSTs gradually warm along the forecast track.
Assuming the overall circulation remains intact, Florence shouldn't
have any problems restrengthening beginning in a day or so. In
fact, guidance suggests that Florence could once again become a
major hurricane in 4 or 5 days. The new NHC intensity forecast is
essentially an update of the previous one, and is only adjusted to
account for recent trends. Largely, the official forecast is close
to the various consensus aids.

Owing to the degraded structure and tilted nature of the system,
Florence has wobbled a bit to the west, but the longer-term motion
estimate is 305/09. Low- to mid-level ridging should cause
Florence to turn toward the west-northwest and west between 12-48
hours while the cyclone recovers from the strong shear. Thereafter,
Florence is anticipated to become a deep cyclone again, but an even
stronger ridge should maintain the west-northwestward motion, at a
faster speed, through day 5. The ridge is forecast to be
sufficiently strong such that some track models show a motion just
south of due west during the next 12-36 hours. Beyond day 3, the
track forecast becomes increasingly uncertain due to differing
evolutions of the steering pattern over the western Atlantic. While
all of the global models show a progressive trough eroding the
ridge, they differ in the strength of the trough and the ridge to
the north of Florida. These differences result in a great deal of
bifurcation in the track guidance, especially among global model
ensemble members, at the end of the forecast period. In such
situations, prudence suggests a reliance on continuity, and the the
new official NHC track forecast is shifted only slightly south
towards the TVCN multi-model consensus and HCCA. It is important to
note that deterministic track models in these types of situations
often display considerable run-to-run changes, and the uncertainty
in this forecast remains larger than normal.

Key Messages:

1. Regardless of Florence's eventual track, large swells will begin
to affect Bermuda on Friday and portions of the U.S. East Coast this
weekend, resulting in life-threatening surf and rip currents.

2. There is still very large uncertainty in Florence's track
beyond day 5, and it is too soon to determine what, if any, other
impacts Florence could have on the U.S. East Coast next week.

3. Since we are near the peak of hurricane season, this is a good
time for everyone who lives in a hurricane-prone area to ensure they
have their hurricane plan in place.

FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 25.0N 49.6W 70 KT 80 MPH
12H 07/0600Z 25.4N 50.7W 60 KT 70 MPH
24H 07/1800Z 25.5N 52.1W 65 KT 75 MPH
36H 08/0600Z 25.5N 53.4W 70 KT 80 MPH
48H 08/1800Z 25.6N 54.6W 75 KT 85 MPH
72H 09/1800Z 26.4N 57.1W 90 KT 105 MPH
96H 10/1800Z 28.0N 61.0W 100 KT 115 MPH
120H 11/1800Z 30.0N 67.0W 105 KT 120 MPH

$$
Forecaster Berg/Rhome

[Hurricane Andrew]

Note how they pin their intensity forecast on the core structure surviving relatively intact...if the shear were to completely TKO this thing, it would change things quite a bit. Just food for thought.

[hipshot]

Note how they pin their intensity forecast on the core structure surviving relatively intact...if the shear were to completely TKO this thing, it would change things quite a bit. Just food for thought.

Yeah, but what I have read so far, I wouldn't want to bet on it petering out. There seems to be enough convection building to ride out the 24 hours of shear until it reaches a much more favorable environment.

[Ptarmigan]

Wow, Florence was a powerful hurricane, now it is a barely a hurricane. Things changed so quickly.

[storm_in_a_teacup]

Note how they pin their intensity forecast on the core structure surviving relatively intact...if the shear were to completely TKO this thing, it would change things quite a bit. Just food for thought.

Yeah, but what I have read so far, I wouldn't want to bet on it petering out. There seems to be enough convection building to ride out the 24 hours of shear until it reaches a much more favorable environment.

"Ride out..." You make it sound like the storm is weathering its own storm.

[hipshot]

Note how they pin their intensity forecast on the core structure surviving relatively intact...if the shear were to completely TKO this thing, it would change things quite a bit. Just food for thought.

Yeah, but what I have read so far, I wouldn't want to bet on it petering out. There seems to be enough convection building to ride out the 24 hours of shear until it reaches a much more favorable environment.

"Ride out..." You make it sound like the storm is weathering its own storm.

Well "ride out" may have been the wrong words, maybe overcome would have been a better choice.

[AnnularCane]

Note how they pin their intensity forecast on the core structure surviving relatively intact...if the shear were to completely TKO this thing, it would change things quite a bit. Just food for thought.

Yeah, but what I have read so far, I wouldn't want to bet on it petering out. There seems to be enough convection building to ride out the 24 hours of shear until it reaches a much more favorable environment.

"Ride out..." You make it sound like the storm is weathering its own storm.

With all that shear, she kind of is.

[EquusStorm]

Am actually pretty surprised at just how battered Florence has been against all the shear. It took the storm down from a cat 4 to a 1 almost overnight and it's feasible it will drop even below cat 1 before shear abates. It's hanging on, but the satellite appearance is pretty pitiful. I just get the feeling it might take a little longer to reorganize after this shear blast than it took to get to cat 4 the first time; it has a lot of structural rebuilding to do

[otowntiger]

Note how they pin their intensity forecast on the core structure surviving relatively intact...if the shear were to completely TKO this thing, it would change things quite a bit. Just food for thought.

Sure that could change things. If Flo is Tko’d she’s gone, so then what is left to discuss?

[1900hurricane]

 https://twitter.com/philklotzbach/status/1037817412815486976

[BobHarlem]

Am actually pretty surprised at just how battered Florence has been against all the shear. It took the storm down from a cat 4 to a 1 almost overnight and it's feasible it will drop even below cat 1 before shear abates. It's hanging on, but the satellite appearance is pretty pitiful. I just get the feeling it might take a little longer to reorganize after this shear blast than it took to get to cat 4 the first time; it has a lot of structural rebuilding to do

How weak will it get, TS, TD, Open wave? Will that fact imply it will get further west/south. The way it's elongating west to east right now makes me wonder.

[cycloneye]

Hurricane Florence Discussion Number 30
NWS National Hurricane Center Miami FL AL062018
500 PM AST Thu Sep 06 2018

Vertical shear has taken its toll on Florence today as evidenced by
a continued degradation of the overall cloud pattern. The
circulation appears tilted, with the low-level center partially
exposed to the southwest of the deep convection. Subjective and
objective Dvorak Current Intensity (CI) numbers have fallen, and a
blend of the various estimates supports an initial intensity of 70
kt.

The intensity forecast is relatively straightforward in the
short-term as shear is expected to remain strong, which should
continue Florence's weakening trend, potentially taking the system
below hurricane strength. By 24 hours, vertical shear is forecast
to decrease, and the SSTs gradually warm along the forecast track.
Assuming the overall circulation remains intact, Florence shouldn't
have any problems restrengthening beginning in a day or so. In
fact, guidance suggests that Florence could once again become a
major hurricane in 4 or 5 days. The new NHC intensity forecast is
essentially an update of the previous one, and is only adjusted to
account for recent trends. Largely, the official forecast is close
to the various consensus aids.

Owing to the degraded structure and tilted nature of the system,
Florence has wobbled a bit to the west, but the longer-term motion
estimate is 305/09. Low- to mid-level ridging should cause
Florence to turn toward the west-northwest and west between 12-48
hours while the cyclone recovers from the strong shear. Thereafter,
Florence is anticipated to become a deep cyclone again, but an even
stronger ridge should maintain the west-northwestward motion, at a
faster speed, through day 5. The ridge is forecast to be
sufficiently strong such that some track models show a motion just
south of due west during the next 12-36 hours. Beyond day 3, the
track forecast becomes increasingly uncertain due to differing
evolutions of the steering pattern over the western Atlantic. While
all of the global models show a progressive trough eroding the
ridge, they differ in the strength of the trough and the ridge to
the north of Florida. These differences result in a great deal of
bifurcation in the track guidance, especially among global model
ensemble members, at the end of the forecast period. In such
situations, prudence suggests a reliance on continuity, and the the
new official NHC track forecast is shifted only slightly south
towards the TVCN multi-model consensus and HCCA. It is important to
note that deterministic track models in these types of situations
often display considerable run-to-run changes, and the uncertainty
in this forecast remains larger than normal.

Key Messages:

1. Regardless of Florence's eventual track, large swells will begin
to affect Bermuda on Friday and portions of the U.S. East Coast this
weekend, resulting in life-threatening surf and rip currents.

2. There is still very large uncertainty in Florence's track
beyond day 5, and it is too soon to determine what, if any, other
impacts Florence could have on the U.S. East Coast next week.

3. Since we are near the peak of hurricane season, this is a good
time for everyone who lives in a hurricane-prone area to ensure they
have their hurricane plan in place.

FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 25.0N 49.6W 70 KT 80 MPH
12H 07/0600Z 25.4N 50.7W 60 KT 70 MPH
24H 07/1800Z 25.5N 52.1W 65 KT 75 MPH
36H 08/0600Z 25.5N 53.4W 70 KT 80 MPH
48H 08/1800Z 25.6N 54.6W 75 KT 85 MPH
72H 09/1800Z 26.4N 57.1W 90 KT 105 MPH
96H 10/1800Z 28.0N 61.0W 100 KT 115 MPH
120H 11/1800Z 30.0N 67.0W 105 KT 120 MPH

$$
Forecaster Berg/Rhome

[EquusStorm]

Its unexpected rapid intensification that yanked it north into the core of the higher shear definitely threw a huge monkey wrench into its future path and intensity. There are so many options on the table right now that it's going to be mostly speculation til we see how much of Flo survives to recover in the aftermath... interesting 1-2 days coming up.

[Ken711]

Am actually pretty surprised at just how battered Florence has been against all the shear. It took the storm down from a cat 4 to a 1 almost overnight and it's feasible it will drop even below cat 1 before shear abates. It's hanging on, but the satellite appearance is pretty pitiful. I just get the feeling it might take a little longer to reorganize after this shear blast than it took to get to cat 4 the first time; it has a lot of structural rebuilding to do

How weak will it get, TS, TD, Open wave? Will that fact imply it will get further west/south. The way it's elongating west to east right now makes me wonder.

But it's forecasted to reintensify back to a category 4 again?

[cycloneye]

Down to Tropical Storm (60 kts) on 00z Best Track:

AL, 06, 2018090700, , BEST, 0, 250N, 498W, 60, 994, TS

[Hurricane Andrew]

Down to Tropical Storm (60 kts) on 00z Best Track:

AL, 06, 2018090700, , BEST, 0, 250N, 498W, 60, 994, TS

Not surprising, she's really struggling.

[bohaiboy]

A friendly reminder to those on the east coast without insurance. Flood insurance doesn't take effect until 30 days after the date of purpose. For FL, GA, SC, NC, if a named storm is above/beyond Longitude 70 and 90 W and Latitude 20 and 38 N, insurance policies cannot be written. For Virginia northward, if a named storm is above/beyond Longitude 65 W and Latitude 30 N insurance policies cannot be written. http://www.sigmaprograms.com/hurricane- ... uidelines/

[LarryWx]

Down to Tropical Storm (60 kts) on 00z Best Track:

AL, 06, 2018090700, , BEST, 0, 250N, 498W, 60, 994, TS

So, due west last 3 hours at 25.0N. Has the north component of motion ended for now?

[toad strangler]

Florence looks hideous. Possible she just packs it in.

[plasticup]

They say this is a hurricane?