ATL: FLORENCE - Post-Tropical - Discussion

[Blinhart]

All these people talking about dry air hindering Flo, forget about it. She has to strong of a Moisture Envelope, and would take something major to disrupt it. She will be just getting stronger and will be able to keep all the dry air away from her until right before landfall, and then it could take until she is completely in land before the dry air gets inside her.

[northjaxpro]

The posts in this forum are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K. For official information, please refer to products from the NHC and NWS.

if this motion continues for the next 2 hours. we will likely see out first short term track adjustment to the west.. probably 1st of many..

This turn of event is exactly what concerned me going back to early last week when telconnection indices signaled a very unusually, strong positive NAO during the initial formative stage of Florence.

This is why never say any area is 100% in the clear if the noted stronger ridging is indeed confirmed later today.

[NDG]

All I know is that Florence has been moving straight west during the past 6 hours or so.

[Shell Mound]

The sharp increase in southwesterly vertical wind shear shortly before landfall is related to the amplification and retrogression of the mid-level trough over the central subtropical North Atlantic. As this trough does so, it erodes and displaces the anticyclone over Florence, resulting in shear. The slowing movement of Florence as it nears the coastline will only enhance the strength of the storm-relative shear, and also result in upwelling of relatively cooler shelf waters as the storm leaves the Gulf Stream. Additionally, the shear vectors will certainly draw in some drier continental air; however, the absence of an approaching large-scale trough from the west mitigates this somewhat. Nevertheless, even if Florence were to strengthen to near-Cat-5 status over the thirty-six hours, the increase in shear and upwelling, owing to both the trough and the reduction in forward speed, will cause significant weakening in the intensity of Florence before landfall. The rate of weakening could well be faster than the initial intensification. I think a Cat-4 landfall is very unlikely, despite the NHC's forecast. Florence, while quite likely to reach Cat-4 status over the Gulf Stream, will probably be a Cat-2 or low-end Cat-3 at landfall. I would go with a peak of 130-135 knots over the Gulf Stream and a landfall intensity of 90-105 knots over eastern NC. This is more in line with climatology for major hurricanes at the latitude of eastern NC.

Florence has already proven you can not go with Climatology with her. There will not be much to cause her to weaken, there is nearly no wind shear forecasted for her in the future. She should be able to get well in the Cat 5 status, Landfall should be at the lowest Cat 4.

I respectfully disagree. I am going by real-time observations and model data (and the best source of all, the official NHC). Climatology only further supports my tentative conclusion. On the GFS, HMON, and HWRF, the convective pattern becomes disheveled as Florence nears landfall, with the CDO eroding on the western flank. This is a classic illustration of southwesterly shear. For the benefit of people who need life-saving information, please provide information that supports your statement in bold. People are putting too much emphasis on the wind threat and ignoring the fact that rain and storm surge will be enormous threats, owing to the peak intensity, slow movement, and large fetch (wind field). As with Katrina and other large, weakening systems, the low pressure at landfall will suggest stronger winds than is actually the case.

[HurricaneEnzo]

Unless Florence encounters some decent wind shear to force dry air into its core I don't see it being much of a problem. It will shunt any dry air away from it unless something forces it in. My understanding of the current forecast is shear will not be an issue until possibly near landfall.

[NDG]

All these people talking about dry air hindering Flo, forget about it. She has to strong of a Moisture Envelope, and would take something major to disrupt it. She will be just getting stronger and will be able to keep all the dry air away from her until right before landfall, and then it could take until she is completely in land before the dry air gets inside her.

No or very little shear no way the dry air surrounding the hurricane will be injected into it. It is creating its own moist environment. We saw this happen all season long so far over the central Pacific.

[ronyan]

A lot depends on the forward speed of Florence as it makes landfall, it may not have much time to weaken or it may have more than expected.

[plasticup]

I would go with a peak of 130-135 knots over the Gulf Stream and a landfall intensity of 90-105 knots over eastern NC. This is more in line with climatology for major hurricanes at the latitude of eastern NC.

For what it's worth, the sea surface temperatures off the SC, NC, and VA coasts are 3-5 degrees Celcius warmer than their 30-year historical average. It is hard to rely on climatology when the climate is changed.

[txwatcher91]

The 1 minute meso images show that as she nears 60W more of a N wobble or motion is occurring. Check it out here. Everything looks on track. The key with Florence landfalling either in SC or NC is going to be how quickly the ridging breaks down.
https://www.tropicaltidbits.com/sat/sat ... roduct=vis

[StormPyrate]

I would go with a peak of 130-135 knots over the Gulf Stream and a landfall intensity of 90-105 knots over eastern NC. This is more in line with climatology for major hurricanes at the latitude of eastern NC.

For what it's worth, the sea surface temperatures off the NC and SC coasts at 3-5 degrees Celcius warmer than their 30-year historical average. It is hard to rely on climatology when the climate is changed.

Would not the depth of the ocean as it approaches also be a factor? What does the shelf off the coast look like there? Warm shallow water or warm deep? and does it make a difference?

[txwatcher91]

The sharp increase in southwesterly vertical wind shear shortly before landfall is related to the amplification and retrogression of the mid-level trough over the central subtropical North Atlantic. As this trough does so, it erodes and displaces the anticyclone over Florence, resulting in shear. The slowing movement of Florence as it nears the coastline will only enhance the strength of the storm-relative shear, and also result in upwelling of relatively cooler shelf waters as the storm leaves the Gulf Stream. Additionally, the shear vectors will certainly draw in some drier continental air; however, the absence of an approaching large-scale trough from the west mitigates this somewhat. Nevertheless, even if Florence were to strengthen to near-Cat-5 status over the thirty-six hours, the increase in shear and upwelling, owing to both the trough and the reduction in forward speed, will cause significant weakening in the intensity of Florence before landfall. The rate of weakening could well be faster than the initial intensification. I think a Cat-4 landfall is very unlikely, despite the NHC's forecast. Florence, while quite likely to reach Cat-4 status over the Gulf Stream, will probably be a Cat-2 or low-end Cat-3 at landfall. I would go with a peak of 130-135 knots over the Gulf Stream and a landfall intensity of 90-105 knots over eastern NC. This is more in line with climatology for major hurricanes at the latitude of eastern NC.

Florence has already proven you can not go with Climatology with her. There will not be much to cause her to weaken, there is nearly no wind shear forecasted for her in the future. She should be able to get well in the Cat 5 status, Landfall should be at the lowest Cat 4.

I respectfully disagree. I am going by real-time observations and model data (and the best source of all, the official NHC). Climatology only further supports my tentative conclusion. On the GFS, HMON, and HWRF, the convective pattern becomes disheveled as Florence nears landfall, with the CDO eroding on the western flank. This is a classic illustration of southwesterly shear. For the benefit of people who need life-saving information, please provide information that supports your statement in bold. People are putting too much emphasis on the wind threat and ignoring the fact that rain and storm surge will be enormous threats, owing to the peak intensity, slow movement, and large fetch (wind field). As with Katrina and other large, weakening systems, the low pressure at landfall will suggest stronger winds than is actually the case.

People in need of life saving information need to rely ONLY on the NHC and not what is posted here in the forum, IMO. The flooding threat is going to be bad if she comes inland and stalls but the wind will also be bad even if she is "only" a category 3. I don't anticipate much if any weakening prior to landfall, the only possible weakening would be from EWRC if one starts but I don't see enough shear to really affect her and weaken her to a category 2 or 3.

[supercane4867]

TXNT21 KNES 101257
TCSNTL
CCA

A. 06L (FLORENCE)

B. 10/1145Z

C. 25.0N

D. 59.4W

E. ONE/GOES-E

F. T5.5/5.5/D1.0/6HRS

G. IR/EIR/VIS

H. REMARKS...CORRECTED FOR INTENSITY AND ANALYSIS. SYSTEM CHARACTERIZED
BY A WMG EYE SURROUNDED BY LG AND EMBEDDED IN LG FOR A DT=5.5 AFTER
ADDING .5 FOR AN EYE ADJUSTMENT. MET AND PT AGREE. FT IS BASED ON DT.

I. ADDL POSITIONS

NIL


...FISHER

[plasticup]

P-3 plane has left Bermuda for reconnaissance of the storm. Great timing, as the satellite presentation has improved so much and this is likely a Cat 3/4 storm. And some location fixes will help is establish whether she is making the WNW turn as expected.

[AtlanticWind]

The 1 minute meso images show that as she nears 60W more of a N wobble or motion is occurring. Check it out here. Everything looks on track. The key with Florence landfalling either in SC or NC is going to be how quickly the ridging breaks down.
https://www.tropicaltidbits.com/sat/sat ... roduct=vis

The ridging never breaks down,that's why Florence moves wnw/nd into the SE US.

[sponger]

Stronger ridging obviously in place. The afternoon Euro run will tell a lot. My brothers wife is pregnant with 2 kids home alone in Wilmington. Told her to leave tonight to stay with family as tomorrow the coastal zoo begins. Parents in Wilmington are staying put which is a good idea if not in a flood zone. Evacuation is going to be far over done and I expect parking lot conditions by Tues afternoon.

[JaxGator]

Wow, Florence is really instenfying this morning. The last best track as Cyclone Eye posted earlier shows that Florence will be upgraded to a Cat 3 at the 11am advisory. Up to 100 knots (115mph).

[plasticup]

TXNT21 KNES 101257
TCSNTL
CCA

A. 06L (FLORENCE)

B. 10/1145Z

C. 25.0N

D. 59.4W

E. ONE/GOES-E

F. T5.5/5.5/D1.0/6HRS

G. IR/EIR/VIS

H. REMARKS...CORRECTED FOR INTENSITY AND ANALYSIS. SYSTEM CHARACTERIZED
BY A WMG EYE SURROUNDED BY LG AND EMBEDDED IN LG FOR A DT=5.5 AFTER
ADDING .5 FOR AN EYE ADJUSTMENT. MET AND PT AGREE. FT IS BASED ON DT.

I. ADDL POSITIONS

NIL


...FISHER

T5.5. That's Cat 3, right?

[N2FSU]

Forecast to be at 25.4 in 4 hours (2pm). Good benchmark to watch.

[NDG]

If not it is very close to being back to a major hurricane, almost due heading since midnight.

[txwatcher91]

The 1 minute meso images show that as she nears 60W more of a N wobble or motion is occurring. Check it out here. Everything looks on track. The key with Florence landfalling either in SC or NC is going to be how quickly the ridging breaks down.
https://www.tropicaltidbits.com/sat/sat ... roduct=vis

The ridging never breaks down,that's why Florence moves wnw/nd into the SE US.

It does on some models. The GFS for example has the ridge weakening enough to allow Florence to turn more NNW prior to landfall. See the 591dm heights here beginning at hour 72 and looping through 108. You can see the 591dm forms a weakness and allows Florence to turn more to the N through it. There is still ridging in place but enough of a weakness for a powerful storm like Florence to find it. By contrast the Euro keeps the ridging a bit stronger hence the further south track. Which scenario occurs remains to be seen but the ridge does indeed weaken or break down depending on which model one looks at.
https://www.tropicaltidbits.com/analysi ... 1006&fh=42