ATL: FLORENCE - Post-Tropical - Discussion

[N2FSU]

NHC isn’t buying the 06z GFS east shift.

[pgoss11]

This is the first time the NHC in their 11:00 discussion mentions the areas they are most concerned with for Florence direct impact:

2. Interests along the U.S. East Coast, particularly from north
Florida through North Carolina, should closely monitor the progress
of Florence, ensure they have their hurricane plan in place, and
follow any advice given by local officials.

[cycloneye]

BULLETIN
Tropical Storm Florence Advisory Number 37
NWS National Hurricane Center Miami FL AL062018
1100 AM AST Sat Sep 08 2018

...FLORENCE BECOMING BETTER ORGANIZED...
...EXPECTED TO STRENGTHEN TO A HURRICANE TONIGHT...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...24.5N 54.3W
ABOUT 835 MI...1340 KM SE OF BERMUDA
ABOUT 715 MI...1150 KM NE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...W OR 265 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...995 MB...29.39 INCHES



WTNT41 KNHC 081453
TCDAT1

Tropical Storm Florence Discussion Number 37
NWS National Hurricane Center Miami FL AL062018
1100 AM AST Sat Sep 08 2018

Florence has undergone a dramatic structural evolution just within
the past 6 hours or so. Vertical shear has decreased just enough
for the storm to take on a more symmetric shape, with convection
developing in a ring around the low-level center, and an elongated
band wrapping around to the northeastern part of the circulation.
The convection has waned a little bit in intensity, however, due to
the presence of dry air, and Dvorak estimates support maintaining
an initial intensity of 55 kt for now. A NOAA P-3 aircraft is
approaching Florence now on a research mission and should provide
some useful data to better assess the storm's intensity.

Recent WindSat microwave data revealed that Florence has a
well-defined low-level ring in the 37-GHz channel, which tends to
be a harbinger of strengthening when environmental conditions are
favorable. Since vertical shear is decreasing and should be 10 kt
or less by later today, and Florence is heading toward a deeper
pool of warm water over the southwestern Atlantic, a significant
phase of intensification is likely to begin by tonight, continuing
through Tuesday or Wednesday. In fact, the official intensity
forecast explicitly shows rapid intensification occurring between
24 and 48 hours from now, and Florence is expected to become a
major hurricane by Monday. The HFIP Corrected Consensus (HCCA) and
the Florida State Superensemble (FSSE), both of which tend to do
well in these scenarios, are both near the upper end of the guidance
suite, especially through day 3. Even by days 4 and 5, the HWRF,
HMON, and ICON intensity consensus are near the top end of the
guidance, close to HCCA and FSSE. Given the signals in the
environment, and the solutions provided by these models, the NHC
intensity forecast shows Florence reaching category 4 intensity by
day 3 and maintains that through the end of the forecast period.

Florence's longer-term motion is 265/6 kt. The cyclone appears to
be slowing down as was expected, and this type of motion is likely
to continue for the next 24-36 hours. In fact, the track guidance
has slowed down during this period, and the updated NHC track
forecast is a little slower than the previous one. After 36 hours,
the most notable change in the models was a northeastward shift in
the 06Z GFS. However, that run appears to be an outlier from the
rest of the dynamical models, and its trend opposes the slight
westward shift noted in the HCCA and FSSE aids. The updated NHC
track forecast is therefore very close to or slightly west of the
previous forecast on days 4 and 5. The exact path of Florence as it
approaches the southeastern U.S. coastline will depend heavily on
the position and strength of the blocking high pressure that is
expected to develop north of Bermuda and extend westward over the
eastern U.S., and so far there has not been much more clarity on
those important details.

Key Messages:

1. Florence is forecast to be a dangerous major hurricane near the
southeast U.S. coast by late next week, and the risk of direct
impacts continues to increase. However, given the uncertainty in
track and intensity forecasts at those time ranges, it's too soon to
determine the exact timing, location, and magnitude of those
impacts.

2. Interests along the U.S. East Coast, particularly from north
Florida through North Carolina, should closely monitor the progress
of Florence, ensure they have their hurricane plan in place, and
follow any advice given by local officials.

3. Large swells are affecting Bermuda and will begin to affect
portions of the U.S. East Coast this weekend, resulting in
life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT 08/1500Z 24.5N 54.3W 55 KT 65 MPH
12H 09/0000Z 24.6N 55.0W 60 KT 70 MPH
24H 09/1200Z 24.6N 56.1W 70 KT 80 MPH
36H 10/0000Z 24.8N 57.5W 85 KT 100 MPH
48H 10/1200Z 25.1N 59.3W 100 KT 115 MPH
72H 11/1200Z 26.3N 64.9W 115 KT 130 MPH
96H 12/1200Z 28.5N 71.5W 125 KT 145 MPH
120H 13/1200Z 31.5N 77.0W 120 KT 140 MPH

$$
Forecaster Berg

[Rail Dawg]

Stay safe Rail Dawg, I know you will.
As always, looking forward to your reports.

Thanks Gcane. I always enjoy your posts.

Was a relatively quiet season.

Stayed here in Houston for Harvey. What a mess. I've got a 23' aluminum boat and joined with the Cajun Navy.

We're still recovering a year later. Water rose 8' in 3 hours around midnight in my neighborhood. It came within 2 doors of our house but 80 of my neighbors were flooded waking up at 2am to water in their bedrooms.

I had just gone to sleep at 11pm after 3 days of rescuing folks. Neighbors pounding on my door to get up and get the boat into the water. Launched right on my street and spent all day getting people to safety.

Wind can be bad but the water really does the damage.

Gasoline/Diesel is like gold as you well know. I carry 80 gallons of diesel and 20 gallons of gas in NATO-certified metal containers when heading into the storm.

[GCANE]

Drop from Kermit.
NW of the CoC
Flo is at about 24N 54W

Air saturated in the low levels, sea to boundary layer.
Basically no directional shear.

[BobHarlem]

I like how the NHC calls out the fact they are forecasting rapid intensification. They usually don't do that, but this may be warranted here.

[chaser1]

It’s not a storm sampling recon, it is a recon to check the upper air around Florence. The recon for Florence itself I can’t remember if it’s sunday or monday

Monday 1130Z

Sorry, just checked
Fixes begin Monday 2330Z.
A couple synoptic missions tomorrow with a Gulfstream IV

Just as pertinent (and interesting), will be the ongoing upper air measurements over the Western States which will continuously offer additional clarity on the depth and timing of the major W. Coast troughing anticipated to occur and mentioned during this 5:00 a.m.'s Hurricane Discussion. Wonder whether there will be an increase in data gathered along the W. Conus region as well?

[hurricaneCW]

NHC isn’t buying the 06z GFS east shift.

I'm glad that the NHC is smart enough to ignore outliers. I believe they even shifted their track a bit further to the left.

[chaser1]

Drop from Kermit.
NW of the CoC
Flo is at about 24N 54W

Air saturated in the low levels, sea to boundary layer.
Basically no directional shear.

Sounds like things are about to pop!

[NC_Cyclone]

Recon just passed through center and had a 990MB reading. Stronger than preiviously thought by a good bit.

[GCANE]

Eyewall looks like its building.
Heavy convection rotating around the CoC leaving cirrus behind.

http://weather.cod.edu/satrad/exper/?pa ... =undefined

[supercane4867]

Recon found pressure around 990mb, winds are about the same with advisory intensity.

[NC_Cyclone]

For those keeping track, a Florence that starts strengthening now gives much credit to a northern track solution.

ALL southern tracks keep Florence from strengthening for the next 2-3 days still.

[SouthDadeFish]

The NOAA P3 flight is finding Florence is approaching hurricane intensity. They found SFMR and flight-level winds of approximately 60 kt. They have yet to sample the NW quadrant. Extrapolated pressures were near 990 mb in the center of the storm.

Edit: A dropsonde splashed in the TC center reporting 991 mb with 9 kt winds, so the central pressure is approximately 990-991 mb.

[Kazmit]

For those keeping track, a Florence that starts strengthening now gives much credit to a northern track solution.

ALL southern tracks keep Florence from strengthening for the next 2-3 days still.

I doubt it will go 2-3 days without strengthening. It seems to have already started, or at least is very close.

[drewschmaltz]

For those keeping track, a Florence that starts strengthening now gives much credit to a northern track solution.

ALL southern tracks keep Florence from strengthening for the next 2-3 days still.

What would be a good chart to look at that has the steering for hurricanes depending on their height? I was just learning this last season from you great people and had a map i could toggle mb on and had the numbers memorized.

I guess a tough year wiped out the specifics.

[Blown Away]

This is the first time the NHC in their 11:00 discussion mentions the areas they are most concerned with for Florence direct impact:

2. Interests along the U.S. East Coast, particularly from north
Florida through North Carolina, should closely monitor the progress
of Florence, ensure they have their hurricane plan in place, and
follow any advice given by local officials.

At this point, got to acknowledge N Florida & Georgia as possible major hurricane landfall even if it hasn't happened in 100+ years...
Something will give likely towards NC IMO...

[Hypercane_Kyle]

Worth pointing out that Florence may not have strengthened at all, those previous MSLP levels were estimates only, whereas the 990-991mb readings are directly observed. It's entirely possible Florence has always been 5-6mb deeper than being portrayed by satellite.

[sponger]

For those keeping track, a Florence that starts strengthening now gives much credit to a northern track solution.

ALL southern tracks keep Florence from strengthening for the next 2-3 days still.

God help the Carolinas!

[KWT]

The NOAA P3 flight is finding Florence is approaching hurricane intensity. They found SFMR and flight-level winds of approximately 60 kt. They have yet to sample the NW quadrant. Extrapolated pressures were near 990 mb in the center of the storm.

Edit: A dropsonde splashed in the TC center reporting 991 mb with 9 kt winds, so the central pressure is approximately 990-991 mb.

It is probably one large convective blast away from putting together Hurricane winds. It's got a great structure, just looking a little bare of deep connection.

Also still looks slight south of West, though a decent lump of convection may help arrest that drop.