ATL: FLORENCE - Post-Tropical - Discussion

[tarheelprogrammer]

Heading close to due west again, correct?

[Hammy]

Here is a GIF image of Isabel's rapid EWRC that transitioned her to a real annularcane.

https://i.imgur.com/rL489AM.gif

this storm is like Isabel's clone, straight down to the possible landfall location.

Wasn't it the same day (Sep 10-11) as well?

[GeneratorPower]

Heading close to due west again, correct?

Stair stepping is pretty common, too. Due west followed by Due north averaging to WNW.

[1900hurricane]

Eyewall replacement continues to progress.

That eyewall is looking rather thin on the northeast side. ERC could have opened a little window for a little dry air intrusion.

Certainly possible. The same microwave pass does show some drier air lurking around the perimeter of the system. Systems do seem to be particularly susceptible to dry air intrusions during eyewall replacement.

[cheezyWXguy]

In regards to the ERC that Florence is likely undergoing and others it will likely undergo in the future, Katrina is a good analog for two examples:

https://www.youtube.com/watch?v=jB7t4KKV38U

1) Katrina underwent a series of ERCs relatively early in its lifespan (much like Florence, in its recent bout of re-strengthening), starting on its first one less than a day after exiting the FL peninsula. The final one in this series took a relatively long time to complete and ultimately resulted in a dramatic change from a compact category 2 to very large category 3, and then to a 5 by the following morning.

2) Katrina underwent a final ERC prior to final landfall, which it failed to complete due to land interaction and dry air intrusion. If Florence does slow down prior to landfall, there is a fair chance it could evolve in a similar fashion (also, Isabel prior to final landfall may be an even better example of this).

[emeraldislenc]

Mandatory evacuation for Emerald Isle starts at 12 noon on Tuesday all visitors and residents should be off the island by 8 pm on Wednesday. The bridge over to the island will be closed to incoming traffic on 7 am on Thursday. Please keep us in your prayers.

[PavelGaborik10]

Certainly continuing to look less an less impressive. Depending on how long the EWRC takes to complete cat 5 window may have closed. Jmo

[meriland29]

What is her position? Is she still gaining latitude or is she jogging more westward? I understand she was wobbling for a bit but unsure if she sustained that

[GeneratorPower]

Mandatory evacuation for Emerald Isle starts at 12 noon on Tuesday all visitors and residents should be off the island by 8 pm on Wednesday. The bridge over to the island will be closed to incoming traffic on 7 am on Thursday. Please keep us in your prayers.

Definitely. Batten the hatches many times over. I hope this storm ends up being the biggest underperformer of all time. Be safe.

[GeneratorPower]

What is her position? Is she still gaining latitude or is she jogging more westward? I understand she was wobbling for a bit but unsure if she sustained that

To me it looks like exactly WNW just as forecasted.

[edu2703]

11:00 PM AST Mon Sep 10
Location: 25.9°N 62.4°W
Moving: WNW at 13 mph
Min pressure: 944 mb
Max sustained: 140 mph



INIT 11/0300Z 25.9N 62.4W 120 KT 140 MPH
12H 11/1200Z 26.5N 64.5W 125 KT 145 MPH
24H 12/0000Z 27.9N 67.5W 130 KT 150 MPH
36H 12/1200Z 29.6N 70.4W 135 KT 155 MPH
48H 13/0000Z 31.3N 73.2W 130 KT 150 MPH
72H 14/0000Z 34.0N 76.5W 120 KT 140 MPH
96H 15/0000Z 35.5N 78.0W 50 KT 60 MPH...INLAND
120H 16/0000Z 36.5N 79.0W 25 KT 30 MPH...INLAND

[cycloneye]

BULLETIN
Hurricane Florence Advisory Number 47
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Mon Sep 10 2018

...FLORENCE CHANGES LITTLE IN STRENGTH DURING THE PAST SEVERAL
HOURS...
...HURRICANE AND STORM SURGE WATCHES LIKELY TO BE ISSUED ON
TUESDAY...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...25.9N 62.4W
ABOUT 465 MI...750 KM SSE OF BERMUDA
ABOUT 1085 MI...1745 KM ESE OF CAPE FEAR NORTH CAROLINA
MAXIMUM SUSTAINED WINDS...140 MPH...220 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 13 MPH...20 KM/H
MINIMUM CENTRAL PRESSURE...944 MB...27.88 INCHES




Hurricane Florence Discussion Number 47
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Mon Sep 10 2018

The rapid intensification of Florence ended just after the last
advisory, with the central pressure falling to near 939 mb. Since
that time, the eyewall convection has become a bit ragged and the
latest central pressure from the Air Force Reserve Hurricane Hunter
aircraft is near 944 mb. The initial intensity will remain a
possibly generous 120 kt for this advisory based on the aircraft
winds. Microwave imagery suggests that Florence may be starting an
eyewall replacement cycle. However, the winds from the Hurricane
Hunter did not clearly indicate the presence of an outer eyewall.

Florence should remain in a light shear environment and over sea
surface temperatures near 29C for at least the next 48 h. Thus,
there is little other than eyewall replacement cycles to keep the
hurricane from intensifying further as indicated by all of the
intensity guidance. The new intensity forecast calls for continued
strengthening to near category 5 strength, although at a slower rate
than what occurred during the last 30 h. Florence is expected to
encounter southwesterly shear near the 72 h point, which could
cause slight weakening before landfall. However, there remains high
confidence that Florence will be a large and extremely dangerous
hurricane, regardless of its exact intensity.

The initial motion is 290/11. A building mid-level ridge over the
northwestern Atlantic is expected to steer Florence
west-northwestward to northwestward with an increase in forward
speed during the next 48 h. After that time, a marked decrease in
forward speed is likely as another ridge builds over the Great
Lakes to the north of Florence. The track guidance continues to
show some spread between the ECMWF on the left side of the envelope
and the GFS on the right side. Overall, though, the guidance has
again shifted a little to the right, and the 72-96 h points are
nudged just a little to the right from the previous forecast. It is
important not to focus on the exact forecast track as average NHC
errors at days 3, 4, and 5 are about 100, 140 and 180 n mi,
respectively, and dangerous hazards will extend well away from the
center.

The NOAA G-IV jet will continue to conduct synoptic surveillance
missions every 12 h through at least Wednesday. In addition, special
0600 UTC and 1800 UTC radiosonde launches have been expanded to
additional upper-air stations across the U.S. to collect extra data
for the numerical models. The next Air Force Reserve Hurricane
Hunter mission into Florence is scheduled for near 12Z.

Key Messages:

1. A life-threatening storm surge is likely along portions of the
coastlines of South Carolina, North Carolina, and Virginia, and
a Storm Surge Watch will likely be issued for some of these areas by
Tuesday morning. All interests from South Carolina into the mid-
Atlantic region should ensure they have their hurricane plan in
place and follow any advice given by local officials.

2. Life-threatening freshwater flooding is likely from a prolonged
and exceptionally heavy rainfall event, which may extend inland over
the Carolinas and Mid Atlantic for hundreds of miles as Florence is
expected to slow down as it approaches the coast and moves inland.

3. Damaging hurricane-force winds are likely along portions of the
coasts of South Carolina and North Carolina, and a Hurricane Watch
will likely be issued by Tuesday morning. Damaging winds could also
spread well inland into portions of the Carolinas and Virginia.

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


FORECAST POSITIONS AND MAX WINDS

INIT 11/0300Z 25.9N 62.4W 120 KT 140 MPH
12H 11/1200Z 26.5N 64.5W 125 KT 145 MPH
24H 12/0000Z 27.9N 67.5W 130 KT 150 MPH
36H 12/1200Z 29.6N 70.4W 135 KT 155 MPH
48H 13/0000Z 31.3N 73.2W 130 KT 150 MPH
72H 14/0000Z 34.0N 76.5W 120 KT 140 MPH
96H 15/0000Z 35.5N 78.0W 50 KT 60 MPH...INLAND
120H 16/0000Z 36.5N 79.0W 25 KT 30 MPH...INLAND

$$
Forecaster Beven

[Chris90]

I think the thing to remember in regards to whether it is an ERC or not is that eyewall cycles typically take time. Sometimes they're faster, sometimes slower, it just depends on the conditions they are working with. To me, you can see in that old microwave image that an ERC was clearly starting. A double wind maximum might not have been overtly apparent yet, but it looks to me like it was just the start of the cycle, so therefore the winds in the outer band would just be starting to increase. You can usually start to pick up on the first signs of the ERC on satellite and microwave when you see that outer band start to develop and strengthen, as that band gets stronger and fully wraps forming the outer eyewall, the winds will start to increase as it gets ready to start choking off the inner eyewall.
So, I think with that microwave image what we were seeing was the start of the outer eyewall, it still has a ways to go. We will have to see with more recon and microwave passes how it is progressing.

As for the annular possibility, if you've been following the EPAC/CPAC this year you would know there have been a couple of annular hurricanes this season over there. Obviously you can look at satellite images for annular characteristics, but in my personal opinion, annular structures really show up well on microwave images using the 85/89/91 gHz band and selecting the color option. The eyewall will show up as a solid red donut with pretty much even, uniform thickness all the way around, and it is fairly uniformly strong throughout with no weaknesses.

[sponger]

Eyewall replacement continues to progress.

That eyewall is looking rather thin on the northeast side. ERC could have opened a little window for a little dry air intrusion.

Certainly possible. The same microwave pass does show some drier air lurking around the perimeter of the system. Systems do seem to be particularly susceptible to dry air intrusions during eyewall replacement.

Is that blue shed????

[GeneratorPower]

I think the thing to remember in regards to whether it is an ERC or not is that eyewall cycles typically take time. Sometimes they're faster, sometimes slower, it just depends on the conditions they are working with. To me, you can see in that old microwave image that an ERC was clearly starting. A double wind maximum might not have been overtly apparent yet, but it looks to me like it was just the start of the cycle, so therefore the winds in the outer band would just be starting to increase. You can usually start to pick up on the first signs of the ERC on satellite and microwave when you see that outer band start to develop and strengthen, as that band gets stronger and fully wraps forming the outer eyewall, the winds will start to increase as it gets ready to start choking off the inner eyewall.
So, I think with that microwave image what we were seeing was the start of the outer eyewall, it still has a ways to go. We will have to see with more recon and microwave passes how it is progressing.

As for the annular possibility, if you've been following the EPAC/CPAC this year you would know there have been a couple of annular hurricanes this season over there. Obviously you can look at satellite images for annular characteristics, but in my personal opinion, annular structures really show up well on microwave images using the 85/89/91 gHz band and selecting the color option. The eyewall will show up as a solid red donut with pretty much even, uniform thickness all the way around, and it is fairly uniformly strong throughout with no weaknesses.

Excellent post.

[cheezyWXguy]

Certainly continuing to look less an less impressive. Depending on how long the EWRC takes to complete cat 5 window may have closed. Jmo

Actually cloud tops have cooled again in the last 10 minutes, and banding features are attempting to pop back up on the east side.

The implications of the ERC are very difficult to forecast for a number of reasons. Duration, change in size, and environmental factors like dry air and shear will play a huge role in how much strengthening will occur after completion, or if it will even complete at all. This ERC could be a saving grace for the east coast if it never completes, or it could result in the structural improvements necessary to capitalize on the very favorable environment and boost this into a large cat5 monster. There is a reason why these processes and their results are so difficult to forecast.

[1900hurricane]

That eyewall is looking rather thin on the northeast side. ERC could have opened a little window for a little dry air intrusion.

Certainly possible. The same microwave pass does show some drier air lurking around the perimeter of the system. Systems do seem to be particularly susceptible to dry air intrusions during eyewall replacement.

Is that blue shed????

In my profile picture? Yup.

[Ken711]

Slow small movements to the right each of the last two NHC updates. It won't take to much for the outer banks to be the probable landfall in a few more update moves.

[sponger]

64 inches of rainfall for Wilmington this year tells me flooding will be apocalyptic uness some dry air shows up before landfall.

[sponger]

Certainly possible. The same microwave pass does show some drier air lurking around the perimeter of the system. Systems do seem to be particularly susceptible to dry air intrusions during eyewall replacement.

Is that blue shed????

In my profile picture? Yup.

I can't believe it was in that good of shape after the beating it took.