ATL: FLORENCE - Post-Tropical - Discussion

[seahawkjd]

When would we normally begin to see watches or warnings posted from the NHC?

Also wow, just realized I've been a member of Storm2k for 12 years now. Doesn't feel like that long haha.

Still quite a while, it has to be 48 hours from landfall. Right now it's a little less than 5 days out.

Not quite. Its 48 hours from the start of expected conditions. Remember that landfall is well after it has started affecting the coast.

[Duddy]

When would we normally begin to see watches or warnings posted from the NHC?

Also wow, just realized I've been a member of Storm2k for 12 years now. Doesn't feel like that long haha.

Still quite a while, it has to be 48 hours from landfall. Right now it's a little less than 5 days out.

Not quite. Its 48 hours from the start of expected conditions. Remember that landfall is well after it has started affecting the coast.

So probably tomorrow then? Tropical storm conditions are forecasted to arrive here in Wilmington Wednesday evening.

[chaser1]

How did you come up with that estimate?

What estimate?

It is pretty clear Florida is in the clear. I just think it is possible for WSW when the ridge fills in and Florence will be on SE side of the high.

It was pretty clear New Orleans was in the clear in 2005 from Katrina before it dived WSW, it was pretty clear E.Texas was in the clear from Ike in 2008, it was pretty clear Florida would be in the clear from Irma before it too went westwards further and further, it was pretty clear Florence was going to be at 30N by 65W, etc...

Weather has a funny way of throwing curveballs, however unlikely they appear at the time. (PS, not me saying it will happen, but still enough time to shift things...

Great great post. It's always "pretty clear" right up to the point when um..... it's no longer pretty clear Look, there are plenty of cases when it is pretty clear and everything evolves pretty much according to plan. Have an approaching hurricane from the southeast with a long-wave pattern that leaves a weakness along the E. Seaboard and yeah, it's "pretty clear" that hurricane will likely re-curve. Maybe it'll get close or maybe it will get partially picked up but left to drift in some N. Atlantic COL for a few days but either way "those" type events are generally clear. I don't find this current blocky pattern to be nearly as clear. The orientation of high pressure ridges, the exact location of Florence in relation to where building heights begin to occur, an unexpected slow or stalled track with Issac fast approaching from the Southeast, etc. Sure, if we look at any particular model for a set number of hours into the future we're looking at a static picture of "what steering is projected to be at that moment). If it's accurate and all other variables are too then it makes sense that the projected outcome will occur. If it were that simple though we wouldn't have multiple models showing different outcomes. A fairly solid consensus among models simply imply they all see the same variables and does better insure a likely outcome. As unlikely as it is to occur though, we have the last couple of years to reflect on where our most reliable global models couldn't accurately predict certain events at a 72 hour time frame. I think any intelligent person would have to side with the likelihood of threat to South or North Carolina. I don't think I've heard one person suggest that outcome might be 50% at best. Nor has anyone boldly suggest or make an argument that Florida is gonna get nailed. In this current set up with a storm moving in a persistent west direction, anyone would be foolish to assume there is no chance that Florida could be directly impacted (even if that chance is well less then 10%).

[Kazmit]

When would we normally begin to see watches or warnings posted from the NHC?

Also wow, just realized I've been a member of Storm2k for 12 years now. Doesn't feel like that long haha.

Still quite a while, it has to be 48 hours from landfall. Right now it's a little less than 5 days out.

Not quite. Its 48 hours from the start of expected conditions. Remember that landfall is well after it has started affecting the coast.

Ah, yes, I forgot. Anyway, the official definitions are here:
https://www.weather.gov/safety/hurricane-ww

[emeraldislenc]

Are the odds highest for a nc strike? Just curious ?

[dukeblue219]

Are the odds highest for a nc strike? Just curious ?

Yes.

It's certainly not guaranteed but that's where everything's pointing right now.

[Ken711]

Are the odds highest for a nc strike? Just curious ?

You can decide as of today subject to change of course.

[emeraldislenc]

That is what my thoughts are too.

[chaser1]

Looking to me like a new fully circular eye wall feature beginning to take shape; not like it won't be about the 3rd or 4th time in recent days. Flo seems to be having a hard time maintaining organization. Lets see.... vertical shear - check, dry air - check.... no reason to think she'll continue to ramp up then. Assuming what I'm seeing is correct then, she's still riding west at about 24.4 N.

[chaser1]

Are the odds highest for a nc strike? Just curious ?

Right now? Yes, easily

[chaser1]

Are the odds highest for a nc strike? Just curious ?

You can decide as of today subject to change of course.

https://my.sfwmd.gov/sfwmd/common/image ... 06_ens.gif

(light blue) Model "COTC" ??

[hipshot]

Looking to me like a new fully circular eye wall feature beginning to take shape; not like it won't be about the 3rd or 4th time in recent days. Flo seems to be having a hard time maintaining organization. Lets see.... vertical shear - check, dry air - check.... no reason to think she'll continue to ramp up then. Assuming what I'm seeing is correct then, she's still riding west at about 24.4 N.

From the last pic I saw, the dry air is pretty much gone, except well south of Flo. Now Isaac, that's a different story, it's surrounded.

[Rail Dawg]

Back in Meteorology 101 when I was a young pup we discussed what was called the Butterfly Theory.

Basically a butterfly flapping it's wings could induce enough disruption to begin the cycle of a thunderstorm if conditions were right.

Yes the ridge is all important now and will remain so for the next 5 days.

However there are a lot of forces at work here and even with today's amazing computing power there's still an uncertainty to where Florence will end up.

If I lived anywhere from the northern FL coast on into NC I wouldn't assume anything is certain for perhaps a couple more days.

A sudden rise in the heights on that ridge just like a butterfly could induce a turn south no one expected.

I'm heading to Wilmington Tuesday morning but know the strike can happen anywhere... even outside the current NHC cone.

[hohnywx]

Are the odds highest for a nc strike? Just curious ?

You can decide as of today subject to change of course.

https://my.sfwmd.gov/sfwmd/common/image ... 06_ens.gif

(light blue) Model "COTC" ??

Coamps...a very rudimentary model.

[Rail Dawg]

About the NHC cone from the NHC website (the bold is mine):

"Historical data indicate that the entire 5-day path of the center of the tropical cyclone will remain within the cone about 60-70% of the time.

To form the cone, a set of imaginary circles are placed along the forecast track at the 12, 24, 36, 48, 72, 96, and 120 h positions, where the size of each circle is set so that it encloses 67% of the previous five years official forecast errors.

The cone is then formed by smoothly connecting the area swept out by the set of circles."

[cycloneye]

BULLETIN
Hurricane Florence Advisory Number 42
NWS National Hurricane Center Miami FL AL062018
500 PM AST Sun Sep 09 2018

...NOAA HURRICANE HUNTER FINDS FLORENCE STRENGTHENING...
...FORECAST TO BECOME A MAJOR HURRICANE ON MONDAY...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...24.4N 57.0W
ABOUT 720 MI...1160 KM SE OF BERMUDA
ABOUT 580 MI...935 KM NE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/H
PRESENT MOVEMENT...W OR 270 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...975 MB...28.80 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.

Interests in the southeastern and mid-Atlantic states should monitor
the progress of Florence.



Hurricane Florence Discussion Number 42
NWS National Hurricane Center Miami FL AL062018
500 PM AST Sun Sep 09 2018

The last reconnaissance fix indicated that the pressure had fallen
to about 978 mb with Florence, a drop of about 6 mb in 4 hours, with
uncontaminated SFMR winds of about 70 kt. Since then, the satellite
presentation has continued to improve, with intensifying deep
convection near the center. Thus the wind speed is set to 75 kt on
this advisory.

Radar data from the NOAA Hurricane Hunter indicated that there were
still a few breaks in the eyewall, possibly allowing some dry air to
mix into the core. This structure has potentially kept Florence
from intensifying rapidly so far. It is likely, however, that the
eyewall will close soon with low environmental shear present,
resulting in a faster intensification rate. The guidance is
remarkably well clustered, with all of the hurricane models showing
category 4 strength within 48 hours, which is uncommon given the
current intensity. The new forecast continues to show rapid
intensification and is increased 5 or 10 kt at most time periods,
but it is still not as high as the Florida State Superensemble or
the NOAA corrected consensus models. It is worth noting that the
model guidance is also significantly increasing the size of
Florence's wind field over the next few days, and the official
forecast reflects this trend.

The fixes from the aircraft indicate that Florence hasn't gained
much latitude yet, and continues moving westward at about 6 kt.
There is no change to the synoptic reason as a very strong ridge is
forecast to build over the northwestern Atlantic during the next few
days. This pattern should steer Florence west-northwestward at a
much faster forward speed by Tuesday. On Wednesday, the hurricane
will likely turn northwestward and slow down somewhat due to another
ridge forming over the Ohio Valley. The most notable change from
the previous advisory is that most of the models are showing a
faster motion in 3 or 4 days, which unfortunately increases the risk
of a destructive hurricane landfall. The GFS and its ensemble mean
are outliers from the main model envelope, showing the system near
the Outer Banks, while the rest of the guidance is well to the
southwest. While a near-miss isn't impossible given the spread of
the ECMWF Ensemble, there is much more support for a track to the
southwest, especially considering the poleward bias of the GFS thus
far this season. Therefore, the official track forecast is shifted a
little bit to the southwest, and is very close to the
corrected-consensus models.

The NOAA G-IV jet is conducting a synoptic surveillance mission this
afternoon to gather data near and around Florence for assimilation
into the numerical models, and these missions will continue through
Tuesday. In addition, upper-air stations across portions of the
central and eastern U.S. are conducting special 0600 UTC and 1800
UTC radiosonde launches to collect extra data for the numerical
models. Hopefully these data will help improve the track and
intensity forecasts.

Key Messages:

1. There is an increasing risk of two life-threatening impacts from
Florence: storm surge at the coast and freshwater flooding from a
prolonged heavy rainfall event inland. While it is too soon to
determine the exact timing, location, and magnitude of these
impacts, interests at the coast and inland from South Carolina into
the mid-Atlantic region should closely monitor the progress of
Florence, ensure they have their hurricane plan in place, and follow
any advice given by local officials.

2. Large swells affecting Bermuda and portions of the U.S. East
Coast will continue this week. These swells will result in
life-threatening surf and rip currents.


FORECAST POSITIONS AND MAX WINDS

INIT 09/2100Z 24.4N 57.0W 75 KT 85 MPH
12H 10/0600Z 24.6N 58.3W 90 KT 105 MPH
24H 10/1800Z 25.1N 60.4W 105 KT 120 MPH
36H 11/0600Z 25.9N 63.1W 115 KT 130 MPH
48H 11/1800Z 27.0N 66.2W 125 KT 145 MPH
72H 12/1800Z 30.3N 72.6W 130 KT 150 MPH
96H 13/1800Z 33.5N 77.5W 120 KT 140 MPH
120H 14/1800Z 35.0N 79.0W 60 KT 70 MPH...INLAND

$$
Forecaster Blake

[CrazyC83]

One question about Recon: how much can it handle? Can it handle concurrent flights into ALL of Florence, Isaac, Olivia and the Gulf low (95L/96L) if all are needed? Or does something have to be held back?

[seahawkjd]

5pm Update:

Location: 24.4°N 57.0°W
Moving: W at 7 mph
Min pressure: 975 mb
Max sustained: 85 mph

[somniture]

You can decide as of today subject to change of course.

(light blue) Model "COTC" ??

Coamps...a very rudimentary model.

COAMPS-TC, a tropical-specific regional model that actually does pretty well with intensity, is not the same thing as COAMPS.

[Blinhart]

I have seen a lot of storms take a WSW dive once a ridge builds in before going west and wnw. It is possible i suppose for this to happen with Florence. Even if it does happen the chances for north florida strike are nil.

How did you come up with that estimate?

What estimate?

It is pretty clear Florida is in the clear. I just think it is possible for WSW when the ridge fills in and Florence will be on SE side of the high.

That is too bold of a statement to say, the likely hood is now for a SC/NC landfall, but with this system still not making the turn the likely hood is slowly converging to a Ga/SC landfall, and I say people from Daytona all the way up to NYC need to keep an eye on this system, this ridge building in will have a major effect and then it retrograding will also have an effect later on