ATL: FLORENCE - Post-Tropical - Discussion

[LarryWx]

My take based on the 12Z model consensus:

- IF Florence gets to north of 30N before 60 W late this weekend, it stays OTS.
- IF Florence gets to 60W and is then not north of 30N, all bets are off for the SE US and Bermuda.

[Hurricaneman]

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.

The GFS did come closer to the correct strength than the Euro so maybe it wasn’t completely off it’s rocker but the mid range intensity is probably complete garbage

[Ntxw]

Based on the NHC forecast, Florence could add another 6-7 units the next 5 days on top of the 4 units processed.

[cycloneye]

Up to cat 2 on 00z Best Track.

AL, 06, 2018090500, , BEST, 0, 204N, 434W, 85, 976, HU

[TheDreamTraveler]

Here's Levi Cowan's take on Florence and the models for tonight

https://www.youtube.com/watch?v=L2BdB7_G1-E&t=2m38s

[Hammy]

Up to cat 2 on 00z Best Track.

AL, 06, 2018090500, , BEST, 0, 204N, 434W, 85, 976, HU

Can't say this was expected at all.

[StruThiO]

Raw t number of 5.3. maybe pushing major hurricane strength??

[gatorcane]

I am also surprised how strong Florence is getting. Thought it would be weaker given the relatively cooler SSTs and more stable environment where it is at now.

[pgoss11]

I am also surprised how strong Florence is getting. Thought it would be weaker given the relatively cooler SSTs and more stable environment where it is at now.

Hopefully Florence will gain more latitude with it continuing to strengthen. The thought was that with some stronger shear and cooler SSTs the storm would weaken or at least maintain it's strength but Florence has other ideas.

[toad strangler]

This should mean more poleward movement especially with weak 500 mb steering ATM

[EquusStorm]

Eye might be trying to clear on IR. Unreal. Forecast to be a <70mph TS in marginal conditions and now not too far off from making a run for major. I really don't envy the difficulty encountered by those responsible for officially forecasting these storms that seem to defy sense.

[StruThiO]

Eye might be trying to clear on IR. Unreal. Forecast to be a <70mph TS in marginal conditions. . .

Yep. Supposedly hostile environment in a supposedly hostile year and the first Cape verde storm of peak season is already showing off.

[Ntxw]

It's not too surprising we are seeing an uptick. Florence is moving into warmer water now that it is starting to move out of the MDR (above 20N). In a few days it will be in sufficiently warm SSTs to sustain a major pretty easily if not already.

[cycloneye]

Hurricane Florence Discussion Number 23
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Tue Sep 04 2018

GOES-16 imagery shows that the eye of Florence has become better
defined during the last several hours, with even some mesovortices
in the eye present on the shortwave infrared channel. Satellite
intensity estimates continue to rise, and the initial wind speed is
set to 85 kt, just below the latest TAFB estimate of 90 kt.

Florence remains on a west-northwestward course at 300/10 kt. This
general course is expected to continue through 36 or 48 hours while
the hurricane remains near the southwestern edge of the subtropical
ridge. After that time, the forecast becomes more uncertain,
depending on the presence of a narrow mid-level ridge over the
north-central Atlantic Ocean. A look at the ensemble guidance
shows a bifurcation developing by day 5, with the ECMWF favoring
a more northward turn, and the UKMET ensembles showing a stronger
ridge and a continuation of a west-northwest track. The new NHC
forecast is adjusted westward at long range, in line with the
corrected-consensus aids, but don't be surprised if this forecast
undergoes some large changes in the next few cycles, given the
split in the guidance.

This intensity forecast is also difficult. Florence certainly has
exceeded expectations during the last day or so, with the hurricane
on the verge of rapidly intensifying during the last 24 hours
despite a marginal environment. Some more strengthening is
called for in the short term to reflect the current trend.
However, the global models continue to insist that southwesterly
shear will increase over the next couple of days which, in
combination with considerable dry air aloft, should cause some
weakening. Later tomorrow, a slow weakening trend should begin and
continue through 48 hours, although not weakening as much as shown
in the past advisory. This can't be considered a high-confidence
prediction in light of what Florence has done so far. On Friday, an
upper-level low could cut off to the south of the cyclone, which
would lessen the shear near Florence, and the hurricane should be
moving over steadily increasing SSTs. Restrengthening is forecast at
long range, and it wouldn't be surprising if the new NHC prediction
turns out to be too low. It is best to be conservative, however,
since the track uncertainty is increasing by the end of the
forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 05/0300Z 20.7N 43.9W 85 KT 100 MPH
12H 05/1200Z 21.5N 45.5W 90 KT 105 MPH
24H 06/0000Z 22.6N 47.6W 80 KT 90 MPH
36H 06/1200Z 23.7N 49.4W 70 KT 80 MPH
48H 07/0000Z 24.7N 50.9W 65 KT 75 MPH
72H 08/0000Z 26.0N 53.5W 65 KT 75 MPH
96H 09/0000Z 27.3N 55.8W 70 KT 80 MPH
120H 10/0000Z 29.0N 57.5W 80 KT 90 MPH

$$
Forecaster Blake

[cycloneye]

New forecast is to remain as hurricane when it weakens a little.Will add much more ACE than anticipated.

INIT 05/0300Z 20.7N 43.9W 85 KT 100 MPH
12H 05/1200Z 21.5N 45.5W 90 KT 105 MPH
24H 06/0000Z 22.6N 47.6W 80 KT 90 MPH
36H 06/1200Z 23.7N 49.4W 70 KT 80 MPH
48H 07/0000Z 24.7N 50.9W 65 KT 75 MPH
72H 08/0000Z 26.0N 53.5W 65 KT 75 MPH
96H 09/0000Z 27.3N 55.8W 70 KT 80 MPH
120H 10/0000Z 29.0N 57.5W 80 KT 90 MPH

[Kazmit]

They also mention that their forecast for reintensification could be conservative. I think it's quite likely that we could see a major out of this.

[galaxy401]

This part of the discussion is interesting. They mention the split in the models.

A look at the ensemble guidance
shows a bifurcation developing by day 5, with the ECMWF favoring
a more northward turn, and the UKMET ensembles showing a stronger
ridge and a continuation of a west-northwest track. The new NHC
forecast is adjusted westward at long range, in line with the
corrected-consensus aids, but don't be surprised if this forecast
undergoes some large changes in the next few cycles, given the
split in the guidance.

[Ntxw]

New forecast is to remain as hurricane when it weakens a little.Will add much more ACE than anticipated.

INIT 05/0300Z 20.7N 43.9W 85 KT 100 MPH
12H 05/1200Z 21.5N 45.5W 90 KT 105 MPH
24H 06/0000Z 22.6N 47.6W 80 KT 90 MPH
36H 06/1200Z 23.7N 49.4W 70 KT 80 MPH
48H 07/0000Z 24.7N 50.9W 65 KT 75 MPH
72H 08/0000Z 26.0N 53.5W 65 KT 75 MPH
96H 09/0000Z 27.3N 55.8W 70 KT 80 MPH
120H 10/0000Z 29.0N 57.5W 80 KT 90 MPH

That 5 day forecast, my math has roughly ~8 units

[TheStormExpert]

This part of the discussion is interesting. They mention the split in the models.

A look at the ensemble guidance
shows a bifurcation developing by day 5, with the ECMWF favoring
a more northward turn, and the UKMET ensembles showing a stronger
ridge and a continuation of a west-northwest track. The new NHC
forecast is adjusted westward at long range, in line with the
corrected-consensus aids, but don't be surprised if this forecast
undergoes some large changes in the next few cycles, given the
split in the guidance.

Large changes is some strong wording!

[JaxGator]

I think also that the models are also taking Florence's forward speed into account as well as the upper air pattern and how fast she'll be at the certain latitude (near or at 30N and 60W ?) caught by the trough or the ridge. Also, the pace Florence is intensifying is impressive.