ATL: FLORENCE - Post-Tropical - Discussion

[Hypercane_Kyle]

Interesting tidbit from the 5:00 PM discussion.

There is a fair amount of north-south
spread in the guidance, with the GFS, GEFS ensemble mean and HWRF on
the right side of the envelope and the ECMWF, ECMWF mean and UKMET
on the left. This spread is likely due to large differences in the
vertical structure of the cyclone, with the ECMWF and UKMET having a
much weaker vortex at 500 mb compared to the GFS in 3-4 days. Given
the difficulty in forecasting these types of structural changes,
the NHC forecast lies in the middle of the guidance envelope and is
close to the multi-model consensus aids through the forecast period.
This forecast is largely an update of the previous NHC prediction.

[plasticup]

Whether she recurves or ducks under the high towards CONUS, it is looking more and more likely that Bermuda will see a brush of this. Or more.

[LarryWx]

IF Florence were to later hit the CONUS as an intact TC, it would tie last year's Irma for the furthest N on record back to 1851 when at 35W, which is ~17.5N.

The next most northerly position when at 35W was likely the formative Ike, which was probably near 17N at 35W although technically not yet born by 35W.

The complete list at 35W at 15N or higher that is on record later hitting the CONUS back to 1851 counting Ike of 2008:

- Irma of 2017 ~17.5N
- Ike of 2008 ~17.0N
- #6 of 1893 ~16.5N
- #6 of 1938 ~16.0N
- Gloria of 1985 ~15.0N

[cycloneye]

00z Best Track remains at 45 kts.

AL, 06, 2018090300, , BEST, 0, 178N, 352W, 45, 1000, TS

[Kazmit]

Crazy how just a couple days ago this was forecasted to recurve hundreds of miles east of any land, and now it looks like a potential east coast threat.

[chaser1]

Crazy how just a couple days ago this was forecasted to recurve hundreds of miles east of any land, and now it looks like a potential east coast threat.

Right?? We've all seen SO many storms re-curve over the years especially those that have gained a fair degree of latitude while still pretty far east. Could Florence still re-curve? Yes. Might other tropical storms that develop in the MDR also re-curve, sure. But this is the year of the ridge. Nothing lasts forever however one thing that I learned about tropical cyclone development and their tracks a long long time ago was pattern persistence. This summer's 500mb flow over the Eastern CONUS and the Atlantic has pretty consistently been like an over-sized Costco bag of Lay's Chips.... nothing but ridges. Seasonal changes occur but until I see significant troughing begin to occur, I've got to believe that most "less then vertically stacked" tropical cyclones will continue to be steered by the broadly established flow. Granted heights have fallen as they typically do in September but this might only imply an increased landfall risk to points further north along the U.S. and Canadian coastline.

[cycloneye]

BULLETIN
Tropical Storm Florence Advisory Number 15
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Sun Sep 02 2018

...FLORENCE CONTINUES TO HOLD STEADY IN STRENGTH OVER THE EASTERN
ATLANTIC...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...17.9N 35.9W
ABOUT 790 MI...1275 KM WNW OF THE SOUTHERNMOST CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...1000 MB...29.53 INCHES




Tropical Storm Florence Discussion Number 15
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Sun Sep 02 2018

Florence has generally changed little during the past several
hours. The cloud pattern consists of a central dense overcast
feature with the low-level center estimated to be closer to the
southern side of the convection. All of the satellite intensity
estimates have held steady and support maintaining the wind speed
at 45 kt.

Although Florence is located in an environment of relatively low
wind shear, the SSTs beneath the cyclone are cool, around 26 deg C.
The tropical storm is expected to move over gradually warmer waters
beginning in about 24 hours, but it will also be moving into an
environment of higher shear. These mixed signals suggest that
Florence will likely change little in intensity or weaken
slightly during the next few days. By the end of the forecast
period, however, the shear is expected to lessen and by then
Florence should be over much warmer waters. Therefore,
strengthening seems likely in the 4 to 5 day time period. The NHC
intensity forecast is a little lower than the previous one to come
into better agreement with the latest guidance.

Florence is moving west-northwestward at 15 kt steered by a
mid-level ridge to its northeast. Although the track models all
show a west-northwestward to northwestward motion during
the next several days, the north-south spread becomes fairly large
by the end of the forecast period. This spread appears to be
primarily associated with differences on how strong or vertically
coherent each model predicts Florence to be. Since the NHC forecast
shows the storm changing little in strength for the next few days,
this track prediction lies near the middle of the guidance envelope
close to the various consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 03/0300Z 17.9N 35.9W 45 KT 50 MPH
12H 03/1200Z 18.3N 38.1W 45 KT 50 MPH
24H 04/0000Z 18.7N 40.6W 45 KT 50 MPH
36H 04/1200Z 19.2N 43.0W 45 KT 50 MPH
48H 05/0000Z 19.8N 45.2W 45 KT 50 MPH
72H 06/0000Z 21.5N 49.6W 40 KT 45 MPH
96H 07/0000Z 23.6N 53.8W 40 KT 45 MPH
120H 08/0000Z 25.5N 56.7W 50 KT 60 MPH

$$
Forecaster Cangialosi

[Mouton]

This storm has the look of another "F" storm, one from 2004...Francis. That ridge has what Bastardi calls the ridge over troubled waters. At 9+ days out, some things could happen but it is equally possible the ridge opens up as it builds west. Lately all the guidance has shifted west. Till that trend changes, that is what is probably going to be the solution and hence it could be a Francis IMO.

[ScottNAtlanta]

I think Jebi is going to dictate how strong the high actually becomes...typhoons that recurve like Jebi can greatly influence the pattern down stream

[LarryWx]

IF Florence were to later hit the CONUS as an intact TC, it would tie last year's Irma for the furthest N on record back to 1851 when at 35W, which is ~17.5N.

The next most northerly position when at 35W was likely the formative Ike, which was probably near 17N at 35W although technically not yet born by 35W.

The complete list at 35W at 15N or higher that is on record later hitting the CONUS back to 1851 counting Ike of 2008:

- Irma of 2017 ~17.5N
- Ike of 2008 ~17.0N
- #6 of 1893 ~16.5N
- #6 of 1938 ~16.0N
- Gloria of 1985 ~15.0N

Further to the above, I counted a total of 42 TCs on record since 1851 that crossed 35W within 15-17.5 N including Ike. Five (the five noted earlier) of the 42 later hit the CONUS or just under 1 in 8. So, whereas the odds are low, they may not be as low as some may have thought.

I counted only 13 that crossed 35W within 18-20N since 1851 on record. None of these later hit the CONUS. The closest (1975) was 500 miles from Cape Cod. These 13 were in 2016, 2013, 2006, 1990, 1989, 1987, 1975, 1967, 1961, 1955, 1934, 1901, and 1892. Just as is the case for those that crossed 35W within 15-17.5N, the frequency of detection picked up greatly with the start of the satellite era, which is intuitive.

[TropicalAnalystwx13]

[cycloneye]

BULLETIN
Tropical Storm Florence Advisory Number 16
NWS National Hurricane Center Miami FL AL062018
500 AM AST Mon Sep 03 2018

...FLORENCE CONTINUES WEST-NORTHWESTWARD...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...18.0N 37.5W
ABOUT 895 MI...1440 KM WNW OF THE SOUTHERNMOST CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES



Tropical Storm Florence Discussion Number 16
NWS National Hurricane Center Miami FL AL062018
500 AM AST Mon Sep 03 2018

The structure of Florence has recovered overnight. Several recent
microwave images indicate that the tropical storm's center is still
dislocated to the south of most of the associated convection, but
convective banding has increased. There is also evidence that
Florence has developed better defined low-level inner-core.
Satellite intensity estimates have increased and now range from 45
to 60 kt. As a compromise of the various estimates, the initial
intensity has been raised slightly to 50 kt, but its worth noting
that this increase is within the noise level of our ability to
observe the intensity of tropical storms over the open ocean.

Based on SHIPS diagnostics, the southwesterly shear affecting
Florence could remain moderate for the next 12 h, and some slight
intensification is possible. However, by 24 h, an increase in the
shear should kick off a gradual weakening trend. By the end of the
forecast period, the tropical storm is forecast to re-intensify
while it moves over warmer SSTs and the environmental shear
decreases. Given the improved current structure of Florence, the new
official intensity forecast shows slight intensification for the
first 12 h. Beyond that time, the models are in good agreement and
the NHC forecast is near the middle of the relatively tight
intensity guidance envelope.

The tropical storm is still moving west-northwestward, at an
estimated 14 kt. A continued west to west-northwest motion is
forecast by all the global models for the next couple of days. By
the end of the forecast period, nearly all of the guidance shows a
turn toward the northwest, and the main source of uncertainty in
the track forecast continues to be exactly when and to what extent
Florence will make this turn. At this point I have no reason to
depart from the various consensus models, and the track forecast is
very close to the previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT 03/0900Z 18.0N 37.5W 50 KT 60 MPH
12H 03/1800Z 18.3N 39.6W 55 KT 65 MPH
24H 04/0600Z 18.7N 42.0W 50 KT 60 MPH
36H 04/1800Z 19.3N 44.2W 45 KT 50 MPH
48H 05/0600Z 20.0N 46.5W 45 KT 50 MPH
72H 06/0600Z 22.2N 51.1W 40 KT 45 MPH
96H 07/0600Z 24.5N 54.5W 45 KT 50 MPH
120H 08/0600Z 26.0N 57.0W 55 KT 65 MPH

$$
Forecaster Zelinsky

[NDG]

If just a few weeks ago one would had told Dr Phil K that there was going to be a fairly good organized CV TS near the 18th latitude and 38th longitude on September 3rd he would had thought he or she would be crazy to think of that, even myself I would had thought that.
BTW, big props to the Euro's weeklies for forecasting the big change over the Atlantic weeks ago.

[Ubuntwo]

Pass showing some 60kt barbs. Could already be a hurricane.

[shiny-pebble]

Definitely a good looking storm. Could be reaching 70MPH.

Sent from my LG-H700 using Tapatalk

[cycloneye]

12z Best Track up to 55 kts. Conservative estimate?

AL, 06, 2018090312, , BEST, 0, 183N, 380W, 55, 997, TS

[RL3AO]

Florence is certainly more organized than the ECMWF was suggesting. Perhaps a plus for the GFS track? We'll see.

[drezee]

Florence is certainly more organized than the ECMWF was suggesting. Perhaps a plus for the GFS track? We'll see.

Let's hope...stay fishy Florence

[gatorcane]

I don’t see Florence gaining much latitude though.

http://rammb.cira.colostate.edu/ramsdis ... display=12

[tolakram]

Florence looking pretty good this morning.

SLIDER: http://rammb-slider.cira.colostate.edu/?sat=goes-16&sec=full_disk&x=17634&y=6975&z=3&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