ATL: FLORENCE - Post-Tropical - Discussion

[HurricaneIrma]

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!

something Monstrous could come out of this thing

[Ptarmigan]

First major hurricane of the Atlantic 2018 season?

[Hurricaneman]

My thing here is if this moves slower than forecast then it may not matter the intensity because the escape hatch will close and this will go west, I can think of 5 possibilities in order from most likely to least

1. A possible Fabian 2003 track. 30%
2. A possible Andrew 1992 Track 25%
3. A track between Bermuda and North Carolina. 20%
4 A possible 1944 hurricane track. 15%
5 Out to sea without impact 10%

So as you can see this could get quite ugly and this will have to be watched

[TheStormExpert]

My thing here is if this moves slower than forecast then it may not matter the intensity because the escape hatch will close and this will go west, I can think of 5 possibilities in order from most likely to least

1. A possible Fabian 2003 track. 30%
2. A possible Andrew 1992 Track 25%
3. A track between Bermuda and North Carolina. 20%
4 A possible 1944 hurricane track. 15%
5 Out to sea without impact 10%

So as you can see this could get quite ugly and this will have to be watched

I wouldn’t say an Andrew track is 25%. More likely 5%, if that.

[cjrciadt]

5.7 Raw T Number

[bob rulz]

Where do people go for their satellite imagery nowadays? The SSD link I used to use for floaters doesn't have the floaters up anymore.

[Sciencerocks]

Where do people go for their satellite imagery nowadays? The SSD link I used to use for floaters doesn't have the floaters up anymore.

Imagine how great a ssd visiable loop would be with the new satellite. Hopefully ssd figures out how to do them for the new satellite soon.

I use weathernerds or tropical tidbits...The problem with them is they're different compared to every other year within the archives I am doing so it is harder to compare storms.

IR is vastly different colors from every other year.
No Dvorak

[Hurricaneman]

First major hurricane of the Atlantic 2018 season?

Almost a certainty

[Chris90]

Where do people go for their satellite imagery nowadays? The SSD link I used to use for floaters doesn't have the floaters up anymore.

Imagine how great a ssd visiable loop would be with the new satellite. Hopefully ssd figures out how to do them for the new satellite soon.

I use weathernerds or tropical tidbits...The problem with them is they're different compared to every other year within the archives I am doing so it is harder to compare storms.

IR is vastly different colors from every other year.
No Dvorak

Here's a link for SSD floaters: http://www.ssd.noaa.gov/PS/TROP/floaters-old.html

Atlantic storms are not updating right now though. They haven't been for a couple days from what I can tell. I've been using that link all summer though to follow the EPAC/CPAC.

I personally am a fan of using the satellite imagery from tropical tidbits, and dvorak imagery is an option there. I just find it the easiest to use since I almost always use my phone, but I can see the appeal of weathernerds if using a PC. I just think that site is a bit more difficult to use on my phone.

Hope that might help a bit.

[bob rulz]

Thanks! I think TropicalTidbits will work well. I don't keep up with tropical weather nearly as much as I used to, since I'm in the heart of pursuing my (non-meteorology) degree, so tracking what looks to be an active September is going to be difficult. Having reliable satellite links helps a lot, since when a big storm comes around it's simply going to be impossible to keep up with every post.

[Sciencerocks]

Where do people go for their satellite imagery nowadays? The SSD link I used to use for floaters doesn't have the floaters up anymore.

Imagine how great a ssd visiable loop would be with the new satellite. Hopefully ssd figures out how to do them for the new satellite soon.

I use weathernerds or tropical tidbits...The problem with them is they're different compared to every other year within the archives I am doing so it is harder to compare storms.

IR is vastly different colors from every other year.
No Dvorak

Here's a link for SSD floaters: http://www.ssd.noaa.gov/PS/TROP/floaters-old.html

Atlantic storms are not updating right now though. They haven't been for a couple days from what I can tell. I've been using that link all summer though to follow the EPAC/CPAC.

I personally am a fan of using the satellite imagery from tropical tidbits, and dvorak imagery is an option there. I just find it the easiest to use since I almost always use my phone, but I can see the appeal of weathernerds if using a PC. I just think that site is a bit more difficult to use on my phone.

Hope that might help a bit.

Thank you.

[Frank2]

The possible good news is a very slow moving Florence in the W Atlantic will break down the ridge completely and recurve whatever else forms behind it - we've seen it happen before.

[cycloneye]

Hurricane Florence Discussion Number 24
NWS National Hurricane Center Miami FL AL062018
500 AM AST Wed Sep 05 2018

Conventional satellite enhanced BD-curve infrared imagery and a
0511 UTC GMI color composite microwave pass reveal improved inner
core structure with impressive outer banding over the eastern
semicircle. Dvorak intensity estimates have again increased, and
the initial intensity is once more increased to 90 kt, which also
agrees with the latest SATCON analysis.

This intensity forecast is still a bit murky. The deterministic
models show increasing southwesterly vertical shear and a less than
favorable mid-tropospheric thermodynamic environment affecting the
tropical cyclone over the next 48 hours. This less-than-conducive
environment should induce weakening during this time frame.
Thereafter, and through the remaining forecast, most of the
models show a mid- to upper-level low developing to the south of
Florence in the base of the mid- Atlantic deep-layer trough, which
should promote a somewhat more favorable diffluent upper wind
pattern. This more conducive upper wind pattern, and increasing sea
surface temperatures, is expected to cause Florence to restrengthen.
The NHC forecast is a little bit higher than the previous one
between the 48 and 96 hr periods to agree more with the IVCN and
NOAA-HCCA consensus forecasts.

Florence is estimated to be moving northwestward, or 305/11 kt,
which appears to be a temporary trochoidal eyewall wobble. A turn
back toward the west-northwest is expected later today, and this
general motion is expected to continue through day 4 while the
hurricane is steered by the southwestern periphery of the
subtropical ridge. By the end of the forecast period, Florence is
expected to turn northwestward and slow down as it enters a break in
the ridge. The ECMWF model track forecast has shifted significantly
toward the left this evening, closer to the other global models and
their ensemble means, indicating less steering influence from the
predicted growing weakness in the subtropical ridge. Subsequently,
an adjustment to the left of of the previous advisory, beyond 48
hours, was made in order to nudge closer to the guidance suite and
the consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 05/0900Z 21.4N 44.8W 90 KT 105 MPH
12H 05/1800Z 22.2N 46.3W 90 KT 105 MPH
24H 06/0600Z 23.2N 48.2W 80 KT 90 MPH
36H 06/1800Z 24.2N 50.0W 70 KT 80 MPH
48H 07/0600Z 24.9N 51.5W 70 KT 80 MPH
72H 08/0600Z 25.6N 54.1W 75 KT 85 MPH
96H 09/0600Z 26.8N 56.3W 80 KT 90 MPH
120H 10/0600Z 28.7N 58.2W 85 KT 100 MPH

$$
Forecaster Roberts

[Shell Mound]

Based on recent satellite imagery, Florence is very likely a 100-knot major hurricane now, with a well-defined eye clearing in the midst of a potent CDO. Early visible images confirm this trend. As with Matthew in 2016, the shear vectors appear to be venting the system rather than shearing it. In fact, the CDO and outflow have expanded westward a bit over the past several hours. Like Beryl, Florence appears to be thriving in an otherwise dry environment. The long-term movement is clearly to the northwest on satellite imagery. Comparison with the 00Z UKMET ensembles shows that Florence is consistently moving to the right of the UKMET in the short term. The WNW movement on the UKMET ensembles clearly isn't happening at this point. Notably, Florence is also persistently to the right of the ECMWF, especially compared to two days ago. The GFS has performed the best in terms of gauging the eastward-biased movement of Florence. However, the GFS has shifted considerably toward the UKMET/ECMWF in the medium to long term, owing to stronger ridging over the Eastern Seaboard, and shows a gradual westward turn commencing in a few days. The timing and amplitude of various troughs relative to Florence's location will be key factors.

06Z GFS: turns W at ~25°N 51°W
00Z UK: turns W at ~24°N 53°W (ensemble mean)
00Z EC: turns W at ~26°N 55°W






Two camps are evident on the 06Z GEFS ensembles by day five (ninety-six hours): a northern camp that feels the initial weakness and heads OTS, and a southern camp that turns W:



Illustrative chart:



Some important Twitter discussions:

 https://twitter.com/JackSillin/status/1037284955045462017



 https://twitter.com/webberweather/status/1037144641618030597



 https://twitter.com/webberweather/status/1037147750218059781



 https://twitter.com/webberweather/status/1037278226710765570



 https://twitter.com/webberweather/status/1037283760654442497



 https://twitter.com/webberweather/status/1037287869323337729

[Ntxw]

Eye needs to warm a bit more but very close to a major. Barring shear, this should be a major soon in the next update.

[Hypercane_Kyle]

Looks likely Florence will be upgraded to a major hurricane during the next advisory, eye has continued to warm.

[NDG]

Gordon could be around for at least 8-12 days, it will be one heck of a ACE maker for the Atlantic Basin.

Edit: I meant to say Florence, Gordon is still in my mind

[tolakram]

Florence

I will be rooting for Florence as long as it misses the US and Bermuda.

[Emmett_Brown]

Regarding ridges, and past observations, I have noticed the following over the years:

- Model trends in the 7-9 day range often continue to change for a bit before they settle down. This W trend may not be done yet. We saw this with Irma and Matthew recently, and notably with Ike a few years back.
- Storms that get shoved W by strong ridges often take on a Southerly component for a while. See Andrew and Katrina.
- While strong storms tend to go more N and be more prone to recurve before threatening the coast, it is not always the case. It all depends on the depth of the steering flow at all levels... so we should not automatically count on a stronger storm automatically going more poleward unless the steering flow allows it.

[Ntxw]

Florence could easily get ~10 units with the latest forecast the next 5 days on top of the 5.6 units already there. Another ~10+ units after that for the following 5 days if it is a major. 25-35 unit system could be had in total.