ATL: DEBBY - Post-Tropical - Discussion

[derpbynature]

The 11 p.m. forecast discussion refers to the storm as "Dolly" erroneously.

Tropical Storm Debby Discussion Number 19
NWS National Hurricane Center Miami FL AL042024
1100 PM EDT Tue Aug 06 2024

Surface, satellite, and radar observations indicate that the
center of Debby has emerged over the Atlantic southeast of
Savannah, Georgia. The system is currently comprised of a large
swirl of shallow to moderate convection with occasional patches of
deep convection, particularly in bands to the east of the center.
GOES-16 airmass imagery indicates that interaction with an
upper-level trough has spread cool/dry air aloft over the low-level
center, making the cyclone look somewhat subtropical. The initial
intensity is held at 35 kt based on Doppler radar winds in the
bands east of the center and a recent 1-minute wind of 31 kt at
NOAA buoy 41008 to the southwest of the center.

Dolly is moving slowly and somewhat erratically eastward, with the
initial motion of 090/4. The track guidance continues to show a
generally eastward motion for the next 12-18 h, taking the center a
little farther away from the coast. After that, a building
mid-level ridge should cause the system to turn northward and move
back inland between 24-36 h. Subsequently, Debby is likely to
accelerate northward and northeastward over the eastern and
northeastern U.S. on the east side of an approaching
mid-latitude trough. The new forecast track has been adjusted a
little to the left of the previous track through 48 h to better
match the consensus models, and it has been adjusted to the right
during the extratropical phase to better match the global model
guidance.

The dry air aloft, the lack of an inner wind core, and the lack of
deep convection suggest that Debby is at best going to strengthen
slowly, and this scenario is supported by the majority of the
intensity forecast guidance. The new intensity forecast calls for
gradual strengthening until the cyclone makes landfall between the
24 and 36 h forecast points. Weakening is expected after landfall,
with Debby expected to become post-tropical around 72 h and
complete transition to an extratropical cyclone by 96 h. The new
intensity forecast is at the high end of the intensity guidance
through 36 h and near the intensity consensus after that.

[Teban54]

My recent joke of "Zombie Debbie" in the Ugliest Storms Ever post aside, looks like Debby may have just pinched off the dry air intrusion with the latest convection. Still a long way to go to tighten up the gigantic COC, much less redevelop a core, however.

[Hurricane Mike]

1130pm Video on Debby for anyone interested
https://www.youtube.com/watch?v=BWBXgQ1kXA4

[derpbynature]

Back to 45mph intensity at 2 a.m., moving ESE at 5 mph.

[IsabelaWeather]

I'd give Debby pretty much a 0% chance to do anything, IMO. I have seen storms spread out like this over warmer water for longer that just never can re consolidate again. Given the short time, cooler water temps, I just don't see Debby doing anything. I don't even see the heavy rain being a real threat now, sure some areas may get a lot and it could be a problem. But a large scale massive flood seems to have not materialized, thankfully.

[wxman57]

I cannot even find any 35 kt wind in Debby offshore. Inland wind is 15 mph or less. The ASCAT I saw around 03Z indicated 30 kts max. Debby's broad, open core will likely remain as such up until the center moves ashore. Don't expect any significant weather near the center. Any squalls will be well north of the track into North Carolina and Virginia. I know that the NHC doesn't want coastal residents to relax, but Debby appears to be a depression, at best. Main threat will be from any additional rainfall. No wind threat in the Carolinas.

[Michele B]

Two storms thus far this season, two extreme ends of the spectrum, yet similar in some ways.

Beryl was ferocious at one time, I think even hit Cat 5. Debby barely made it to 1 for a brief second.


Yet both will end up being memorable And their damage due to water rather than wind is what will cost the sufferers.

Strange start to the season.

[Ronel2020]

This has certainly been a strange storm. In Charleston, we had a lot of rain Monday into Tuesday morning, but not much since then. I’ve talked a few people to our south that had a lot of flooding to deal with and some reports of people being stuck at their homes due to roads being washed out in SC and GA.

Wind seems to be picking up a little this morning, but it is still not more than 15-20. The greys reef buoy is reporting some 25-30 KT winds. The satellite loops seem to indicate that Debby is trying to rebuild some clouds closer to the center. All in all, it will be interesting to see if we get anymore significant rain out of this storm or not.

[ColdMiser123]

I cannot even find any 35 kt wind in Debby offshore. Inland wind is 15 mph or less. The ASCAT I saw around 03Z indicated 30 kts max. Debby's broad, open core will likely remain as such up until the center moves ashore. Don't expect any significant weather near the center. Any squalls will be well north of the track into North Carolina and Virginia. I know that the NHC doesn't want coastal residents to relax, but Debby appears to be a depression, at best. Main threat will be from any additional rainfall. No wind threat in the Carolinas.

Definitely not a depression - recon finding plenty of SFMR near 50 kt on the southeast side of the storm.

[cycloneye]

I cannot even find any 35 kt wind in Debby offshore. Inland wind is 15 mph or less. The ASCAT I saw around 03Z indicated 30 kts max. Debby's broad, open core will likely remain as such up until the center moves ashore. Don't expect any significant weather near the center. Any squalls will be well north of the track into North Carolina and Virginia. I know that the NHC doesn't want coastal residents to relax, but Debby appears to be a depression, at best. Main threat will be from any additional rainfall. No wind threat in the Carolinas.

Still there are winds above 50kt according to the VDM but those are well separated from the center.

VORTEX DATA MESSAGE AL042024
A. 07/11:25:30Z
B. 32.20 deg N 079.44 deg W
C. 925 mb 661 m
D. EXTRAP 997 mb
E. NA
F. NA
G. NA
H. 32 kt
I. 315 deg 29 nm 11:16:30Z
J. 032 deg 32 kt
K. 315 deg 27 nm 11:17:00Z
L. 52 kt
M. 131 deg 95 nm 11:56:00Z
N. 221 deg 64 kt
O. 131 deg 113 nm 12:02:00Z
P. 19 C / 876 m
Q. 21 C / 876 m
R. 17 C / NA
S. 1234 / 9
T. 0.02 / 3 nm
U. AF309 0904A DEBBY OB 04
MAX FL WIND 64 KT 131 / 113 NM 11:17:00Z
SLP EXTRAP FROM 925 MB
MAX FL TEMP 21 C 307 / 8 NM FROM FL CNTR
;

[cheezyWXguy]

I cannot even find any 35 kt wind in Debby offshore. Inland wind is 15 mph or less. The ASCAT I saw around 03Z indicated 30 kts max. Debby's broad, open core will likely remain as such up until the center moves ashore. Don't expect any significant weather near the center. Any squalls will be well north of the track into North Carolina and Virginia. I know that the NHC doesn't want coastal residents to relax, but Debby appears to be a depression, at best. Main threat will be from any additional rainfall. No wind threat in the Carolinas.

Definitely not a depression - recon finding plenty of SFMR near 50 kt on the southeast side of the storm.

Honestly wasn’t expecting that. With how flat the pressure gradient is, no organized convection, and seemingly no temp increase during the center pass, does this meet the definition of anything more than a remnant low?

[wxman57]

Debby doesn't even appear tropical now. Looks like a front extending to NE. No squalls where the plane found the stronger wind.

[zzzh]

AL, 04, 2024080712, , BEST, 0, 322N, 794W, 50, 995, TS,

[syfr]

Debby doesn't even appear tropical now. Looks like a front extending to NE. No squalls where the plane found the stronger wind.

Yeah, not a lot of structure left, nor even a lot of rain bands .

Time will tell.

[Steve]

Debby doesn't even appear tropical now. Looks like a front extending to NE. No squalls where the plane found the stronger wind.

Yeah, not a lot of structure left, nor even a lot of rain bands .

Time will tell.

FV3 still has most of SC > 2" up to around a foot through 39 hours from 8am EDT this morning.
https://www.tropicaltidbits.com/analysi ... 0712&fh=43

Through 60 hours, NAM 12km has a foot or so along the NC/SC border and into eastern NC.
https://www.tropicaltidbits.com/analysi ... 0712&fh=60

HRRR has most of the rain concentrated in eastern NC
https://www.tropicaltidbits.com/analysi ... 0712&fh=48

So plenty more rain from the mesoscale models, just not biblical level.

[syfr]

Those are really useful animations.

I know I had 10" of rain overnight when Fran came overhead and we didn't flood, so I suspect we'll be good with this one, if the winds stay down (and the trees stay up)

[LarryWx]

 I estimate that I’m at 8.5” so far from Debby (over last ~30 hours) with only ~1/2” since 2AM allowing good progress on drainage. If we were to not get too much more from this point forward (where I’m leaning now), I’d be near the low end of the range of predictions, which had a pretty good amount for today and tomorrow. As of last night I had guessed at least another 4” between then and Thursday. Still an 8.5” rain is enough to qualify as a very big rain event due to its rarity and likely is the largest since Matthew of early Oct of 2016. Also, some nearby areas (Effingham and Jasper counties) got 10-11” per CoCoRaHS.

 The storm is currently centered just E of here along the coast about to be offshore. Winds and rain are very light near the storm center.

10.12" Lady's Island here started measuring Sunday at 7PM till this AM at 7AM, it wasn't as bad as I thought, some areas have some flooding however nothing too serious near me. Most major roadways accessible. Matthew was rough, and a notable mention to Joaquin and the moisture swath it created over SC from a digging trough

Joaquin didn’t do much in this area. We got ~1”. The setup with Joaquin was unlike anything I have ever seen!

As the Debby center moved to the SE offshore finally putting us on the backside, winds picked up somewhat and steady mainly moderate rains resumed about 2 hours ago after little rain since late last night. I had been at ~8.5” for the storm before this. We’ll see how much gets added from this and more to come tonight.

Further to the above’s 8.5”, I’ve gotten an additional 1.8” since ~6PM yesterday for an updated total so far of ~10.3”, easily the largest amount from a single event since Matthew of early Oct of 2016.
There’s still on and off light rain falling and it’s breezy here on the backside.

[Kazmit]

Up to 50kts bizarrely

[Steve]

Up to 50kts bizarrely

I mean this looks not that far off.

https://www.youtube.com/live/xVEe1tEZ-7 ... YS4sywRHIo

[cycloneye]