ATL: FLORENCE - Post-Tropical - Discussion

[Hurricaneman]

Looks to be going through sw shear right now doesn’t look as good as it has even seem to have weakened a bit

[cycloneye]

Tropical Storm Florence Discussion Number 20
NWS National Hurricane Center Miami FL AL062018
500 AM AST Tue Sep 04 2018

Florence's cloud pattern has changed very little during the past
several hours, with the exception of a possible small Central Dense
Overcast developing just to the east of the center. An earlier
AMSR2 overpass revealed a rather obvious tilt toward the
east-northeast, indicative of the moderate southwesterly shear.
The initial intensity is held a 60 kt, and is supported by the
Dvorak subjective and objective T-numbers.

Florence should exhibit little change in strength during the next
24 hours or so, as the cyclone traverses marginally warm sea surface
temperatures and is influenced by modest west-southwesterly shear.
Slight weakening is expected during the mid- forecast period as the
shear gradually increases with time. Afterward, the upper-level
wind environment should become a little more favorable and, at the
same time, Florence will be moving back over warmer SSTs.
Consequently, the cyclone should gradually strengthen through day 5.
This forecast is unchanged from the previous one, and is in good
agreement with the NOAA-HCCA guidance.

The initial motion estimate is west-northwestward, or 290/11 kt.
The cyclone is expected to be steered west-northwestward for the
next 48 hours by a mid- to upper tropospheric ridge anchored to
the north, followed by a northwestward turn around the 72 hr period
as it enters a growing weakness in the aforementioned ridge. A
rather large spread in the global and hurricane models remains
particularly beyond day 4, however, the consensus models and the
global ensemble means have have been fairly consistent from run to
run. This forecast is just a bit to the north of the previous
advisory and just south of the consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 04/0900Z 19.3N 42.0W 60 KT 70 MPH
12H 04/1800Z 19.9N 43.7W 60 KT 70 MPH
24H 05/0600Z 20.8N 45.8W 60 KT 70 MPH
36H 05/1800Z 21.8N 48.0W 55 KT 65 MPH
48H 06/0600Z 22.9N 50.2W 50 KT 60 MPH
72H 07/0600Z 25.2N 53.4W 50 KT 60 MPH
96H 08/0600Z 27.1N 55.6W 55 KT 65 MPH
120H 09/0600Z 29.1N 57.7W 65 KT 75 MPH

$$
Forecaster Roberts

[tolakram]

Looks to be strengthening again in the visible this morning.

http://rammb-slider.cira.colostate.edu/?sat=goes-16&sec=full_disk&x=16833&y=6805&z=4&im=12&ts=1&st=0&et=0&speed=130&motion=loop&map=1&lat=0&p%5B0%5D=1&opacity%5B0%5D=1&hidden%5B0%5D=0&pause=0&slider=-1&hide_controls=0&mouse_draw=0&s=rammb-slider

[cycloneye]

12z Best Track up to Hurricane:

AL, 06, 2018090412, , BEST, 0, 194N, 418W, 65, 990, HU

[plasticup]

12z Best Track up to Hurricane:

AL, 06, 2018090412, , BEST, 0, 194N, 418W, 65, 990, HU

Anyone else a little surprised by this? I didn't think she looked much different. Couple bursts of convection this morning but...

[chaser1]

12z Best Track up to Hurricane:

AL, 06, 2018090412, , BEST, 0, 194N, 418W, 65, 990, HU

Anyone else a little surprised by this? I didn't think she looked much different. Couple bursts of convection this morning but...

Does look to be tucking it's eye well within the convective COC with an expanding band on it's west quadrant

[cycloneye]

Hurricane Florence Discussion Number 21
NWS National Hurricane Center Miami FL AL062018
1100 AM AST Tue Sep 04 2018

Florence's structure has gradually increased in organization, with
SSMIS passes from a few hours ago revealing the development of a
mid-level microwave eye. Dvorak estimates have responded in
kind--TAFB is up to T4.0, SAB is at T4.5, and the objective ADT is
in between at T4.4. Since there still appears to be moderate
southwesterly shear inducing some tilt to the cyclone and
disrupting the infrared satellite pattern, the initial intensity is
raised conservatively to 65 kt, making Florence a hurricane.

The current motion remains west-northwestward, or 295/10 kt, with
Florence positioned near the southwestern edge of the subtropical
ridge. The steering pattern ahead of Florence is rather complicated
and will be evolving over the next few days. A large and complex
mid-/upper-level trough located northeast of the Leeward Islands is
expected to give way to the development of two upper-level highs
centered near the Greater Antilles and southwest of the Azores, with
Florence slowing down and turning northwestward between these new
features. Despite this complex pattern, the spread in the track
models is less than normal, which increases the confidence in the
NHC track forecast for the next 5 days. There is some spread which
begins to develop around day 5, with the ECMWF model moving Florence
a little faster toward the north while the GFS maintains a slower
speed and keeps the system to the south. The updated NHC track
forecast has been nudged slightly to the east of the previous
forecast on days 4 and 5, close to the TVCX consensus but not as far
as the HCCA and ECMWF models. There is still too much model spread
after day 5 to speculate what Florence might do beyond the official
forecast period.

Despite Florence becoming a hurricane, the southwesterly shear
affecting the cyclone is expected to increase over the next day or
two, which should prevent further intensification. In fact, the
increasing shear, as well as mid-level relative humidities below 50
percent, should cause weakening between 24 and 72 hours. After 72
hours, decreasing shear and warmer sea surface temperatures should
foster some re-intensification, with Florence expected to reattain
hurricane intensity by day 5. The intensity guidance is in good
agreement, and the NHC forecast is very close to a blend of HCCA,
the Florida State Superensemble, and the ICON consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 04/1500Z 19.7N 42.5W 65 KT 75 MPH
12H 05/0000Z 20.3N 44.0W 65 KT 75 MPH
24H 05/1200Z 21.3N 46.2W 65 KT 75 MPH
36H 06/0000Z 22.4N 48.2W 60 KT 70 MPH
48H 06/1200Z 23.6N 50.0W 55 KT 65 MPH
72H 07/1200Z 25.6N 52.7W 50 KT 60 MPH
96H 08/1200Z 27.5N 55.0W 55 KT 65 MPH
120H 09/1200Z 29.5N 56.5W 65 KT 75 MPH

$$
Forecaster Berg

[cycloneye]

...FLORENCE BECOMES THE THIRD HURRICANE OF THE ATLANTIC SEASON...
...NO THREAT TO LAND THROUGH THE WEEKEND..

[plasticup]

Do you have a satellite link? The TropicalTidbits one is having some problems.

[plasticup]

There is still too much model spread
after day 5 to speculate what Florence might do beyond the official
forecast period.

Words to live by

[LarryWx]

It appears to me that based on the last few ensemble runs of various models, the more it weakens the next few days, the less confidence for OTS from the US. The smaller, weaker members seem to be the ones at most risk for going back west enough to hit the US. So, for those who don't want it near there, root for less weakening as this week goes forward.
Based on climo, alone, the smart bet is easily an OTS from US bet, regardless. Bermuda is at higher risk.

[plasticup]

Eye-like feature appearing in the last couple of hours.

[JaxGator]

It's been impressive to watch Florence seeming to plow through dry air/SAL and shear, and still strengthen. The few times it's a good thing to root for a strengthening of a now hurricane to help it go out to sea (besides admiring it from afar). I'm still watching closely regardless and will until Florence has turned away from land (including Bermuda).

[wx98]

Hurricane Florence Tropical Cyclone Update
NWS National Hurricane Center Miami FL AL062018
250 PM AST Tue Sep 04 2018

...FLORENCE CONTINUING TO STRENGTHEN...

Recent satellite imagery indicates that Florence has continued to
intensify during the past few hours, and maximum sustained winds
have increased to 85 mph (140 km/h). This increase in intensity
will be reflected in the forecast issued with the 500 PM AST (2100
UTC) advisory package.


SUMMARY OF 250 PM AST...1850 UTC...INFORMATION
---------------------------------------------------
LOCATION...20.0N 42.7W
ABOUT 1265 MI...2035 KM ENE OF THE LESSER ANTILLES
MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...984 MB...29.06 INCHES

$$
Forecaster Brennan/Berg

Moving on up and heading to warmer water

[Kazmit]

I remember the GFS got some heat for showing Florence instensifying while the Euro kept it weak. Looks like the GFS may be right after all.

[AxaltaRacing24]

I remember the GFS got some heat for showing Florence instensifying while the Euro kept it weak. Looks like the GFS may be right after all.

It was showing a solid cat 2 by now though.

[cycloneye]

Hurricane Florence Tropical Cyclone Update
NWS National Hurricane Center Miami FL AL062018
250 PM AST Tue Sep 04 2018

...FLORENCE CONTINUING TO STRENGTHEN...

Recent satellite imagery indicates that Florence has continued to
intensify during the past few hours, and maximum sustained winds
have increased to 85 mph (140 km/h). This increase in intensity
will be reflected in the forecast issued with the 500 PM AST (2100
UTC) advisory package.


SUMMARY OF 250 PM AST...1850 UTC...INFORMATION
---------------------------------------------------
LOCATION...20.0N 42.7W
ABOUT 1265 MI...2035 KM ENE OF THE LESSER ANTILLES
MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...984 MB...29.06 INCHES

$$
Forecaster Brennan/Berg

[wx98]

I remember the GFS got some heat for showing Florence instensifying while the Euro kept it weak. Looks like the GFS may be right after all.

It was showing a solid cat 2 by now though.

Well I think it’s understood that global models can’t be expected to be right on, even 24 hours out. The thing to notice is that it did predict strengthening, regardless of how much at whatever point.

[cycloneye]

Florence will pump plenty of ACE to help the Atlantic not stay well below average. So far Florence has obtained 3.5 units and the North Atlantic has 22.2 units.

[cycloneye]

Hurricane Florence Discussion Number 22
NWS National Hurricane Center Miami FL AL062018
500 PM AST Tue Sep 04 2018

Despite being over marginally warm water and in an environment of
moderate west-southwesterly shear, Florence's intensity has
increased during the day. The hurricane has a cloud-filled eye in
visible imagery, and the central dense overcast is becoming more
symmetric. Based on Dvorak estimates of T4.5 from TAFB and SAB,
and a SATCON estimate of 77 kt, the initial intensity is now,
somewhat surprisingly, 75 kt. Since the current intensification
trend may not be over, the official forecast calls for Florence to
strengthen just a little more during the next 6-12 hours. Even
though the hurricane will be moving over progressively warmer
waters, increasing vertical shear and dry air in the middle levels
of the atmosphere should induce some weakening in the 24-72 hour
time frame. Lower shear after 72 hours will likely allow Florence
to regain hurricane strength by the end of the forecast period.
The NHC intensity forecast is primarily adjusted to account for the
recent strengthening trend, and is closest to the Florida State
Superensemble and HCCA guidance.

Florence remains on a west-northwestward course at 300/10 kt. This
trajectory is expected to continue through 36 hours while the
hurricane remains near the southwestern edge of the subtropical
ridge. After 36 hours, Florence is expected to turn northwestward
and slow down as it enters a break in the ridge. The track models
are in good agreement and show little spread through 48 hours. On
days 3-5, the biggest outlier is the UKMET, which lies to the south
of the guidance suite. In fact, the bulk of the models, including
the deterministic GFS and ECMWF, are all now showing a more
definitive poleward motion by day 5. While the official NHC track
forecast reflects this thinking, there is still considerable spread
among the associated global model ensembles, and the longer-term
forecast should be considered low confidence.

FORECAST POSITIONS AND MAX WINDS

INIT 04/2100Z 20.3N 43.2W 75 KT 85 MPH
12H 05/0600Z 21.0N 44.8W 80 KT 90 MPH
24H 05/1800Z 22.1N 46.8W 75 KT 85 MPH
36H 06/0600Z 23.2N 48.7W 65 KT 75 MPH
48H 06/1800Z 24.3N 50.4W 60 KT 70 MPH
72H 07/1800Z 26.0N 53.0W 55 KT 65 MPH
96H 08/1800Z 27.5N 55.0W 60 KT 70 MPH
120H 09/1800Z 29.5N 56.5W 70 KT 80 MPH

$$
Forecaster Berg