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Hurricane Debby

Interpretation: winging it as it happens.
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Tropical Depression Four Discussion Number 3
NWS National Hurricane Center Miami FL AL042024
1100 PM EDT Fri Aug 02 2024

Shortwave infrared satellite imagery, Cuban radar data, and surface
observations from Cuba and the Cayman Islands suggest that the
disturbance has developed a closed circulation, and the center is
located just off the south coast of Cuba. Deep convection is still
a bit fragmented, but there has been a persistent burst near the
estimated center since earlier this afternoon. The wind and
pressure field could still be a little elongated within the
southern semicircle, but overall the system appears to have enough
organization to now be designated as a tropical depression. The
initial intensity remains 25 kt based on earlier observations.

The depression has not begun to turn yet, and the initial motion is
west-northwestward, or 285/15 kt. A turn toward the northwest and
then north is expected over the weekend due to a break in the
subtropical ridge caused by a trough over the eastern United
States. Since the system has not started to turn yet, this has
caused all of the track guidance to shift west, and the updated NHC
forecast is a bit west of the previous forecast along the eastern
edge of the main cluster of models. It is important to note that
because of the forecast track being parallel to the west coast of
Florida, the location and timing of a potential landfall cannot be
pinned down at this time. One additional significant change to the
forecast is that the models seem to be showing the aforementioned
trough leaving the cyclone behind early next week, which causes a
much slower motion while the system is near the coasts of Georgia
and South Carolina. As a result, the new NHC forecast is notably
slower than the previous forecast, particularly on days 4 and 5.

The westward shift to the track forecast now also keeps the system
over the warm waters of the Gulf of Mexico longer, giving the
system additional time to potentially strengthen. In fact, the
SHIPS guidance and all of the regional hurricane models show the
cyclone reaching hurricane strength before reaching land in the Big
Bend region of Florida in 2 to 3 days. As a result, the new NHC
forecast brings the intensity to 60 kt at 60 hours as the system is
reaching land, but if model trends continue, it's possible that
future forecasts could explicit show the system becoming a
hurricane before it reaches land. The intensity forecast is more
uncertain on days 3 through 5 due depending on if the center moves
back offshore or stays inland over the southeastern United States.


Key Messages:

1. Heavy rainfall may result in locally considerable flash and urban
flooding across portions of Florida and the coastal areas of the
Southeast U.S. this weekend through Wednesday. Isolated river
flooding will also be possible.

2. Tropical storm conditions are expected Saturday night within the
Tropical Storm Warning area in southwest Florida from East Cape
Sable to Boca Grande and on the Dry Tortugas. Tropical storm
conditions are possible in the remainder of the Florida Keys on
Saturday and along the Florida west coast north of Boca Grande to
Suwannee River Saturday night and Sunday where a Tropical Storm
Watch is in effect.

3. There is a possibility of life-threatening inundation from storm
surge along portions of the west coast of Florida from Bonita Beach
to Suwannee River, including Tampa Bay and Charlotte Harbor, where a
Storm Surge Watch is in effect.

4. Impacts from storm surge, strong winds, and heavy rains are
possible elsewhere in Florida and along the southeast coast of the
United States from Georgia to North Carolina through the middle of
next week, and interests in those areas should continue to monitor
the progress of this system. Additional watches and warnings will
likely be required on Saturday.


FORECAST POSITIONS AND MAX WINDS

INIT 03/0300Z 21.4N 79.7W 25 KT 30 MPH
12H 03/1200Z 22.6N 81.4W 30 KT 35 MPH...OVER CUBA
24H 04/0000Z 24.6N 83.3W 35 KT 40 MPH...OVER WATER
36H 04/1200Z 26.6N 84.1W 45 KT 50 MPH
48H 05/0000Z 28.4N 84.0W 55 KT 65 MPH
60H 05/1200Z 29.9N 83.4W 60 KT 70 MPH...INLAND
72H 06/0000Z 30.8N 82.5W 40 KT 45 MPH...INLAND
96H 07/0000Z 31.8N 80.9W 45 KT 50 MPH...OVER WATER
120H 08/0000Z 32.8N 79.4W 55 KT 65 MPH
 
Chazwin said:
I think if it had gone out further, the EURO would have still turned back to the NW but not as sharply as the 12z run…probably into CHS and then NNW from there. At this frame, the high is building into New England.
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Most likely. I imagine it would also have been stronger as well
 
Cone has shifted north-west some to include all of upstate SC. Euro may be on to something with major inland north west hook.
 
Kinda dropping the ball without a hurricane watch for Florida. IMO there’s enough guidance for it. Interesting to note they said they don’t even know if Debby will go into the Atlantic at all. Hmm
 
Based off of the 18z runs the storm is WNW of their initialization. Looking forward to seeing the 00z runs to see what they depict.
 
BirdManDoomW said:
Kinda dropping the ball without a hurricane watch for Florida. IMO there’s enough guidance for it. Interesting to note they said they don’t even know if Debby will go into the Atlantic at all. Hmm
Click to expand...
I think that means that they don't have a clue.
 
MOV8-4.04L.GIF


Editing to add this map does update but sometimes it's more than an hour behind..
 
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BirdManDoomW said:
no change from me from a couple of days ago. I may tick east in later updates if the storm gets stronger than forecast and speeds up crossing Florida. This will cut down on impacts north of Myrtle Beach. But for now, sig. flood likely in areas belowView attachment 149228
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Looks like the ocean is going to see a lot of flooding per your map
 
0Z UK: landfall just E of 12Z’s Apalachicola; then goes inland further W into C GA then turns E to CHS, goes up SC coast and then well inland into NC; flooding threat many areas:

NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 24 HOURS
FORECAST POSITION AT T+ 24 : 23.5N 83.7W

LEAD CENTRAL MAXIMUM WIND
VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)
-------------- ---- -------- ------------- -------------
0000UTC 04.08.2024 24 23.5N 83.7W 1007 28
1200UTC 04.08.2024 36 25.7N 84.8W 1006 34
0000UTC 05.08.2024 48 27.4N 85.5W 1004 43
1200UTC 05.08.2024 60 28.8N 85.3W 1003 42
0000UTC 06.08.2024 72 29.9N 84.4W 1002 35
1200UTC 06.08.2024 84 31.4N 84.2W 1001 36
0000UTC 07.08.2024 96 32.5N 83.3W 997 37
1200UTC 07.08.2024 108 32.5N 81.1W 996 41
0000UTC 08.08.2024 120 32.8N 79.9W 994 43
1200UTC 08.08.2024 132 33.8N 79.5W 996 41
0000UTC 09.08.2024 144 35.3N 78.4W 998 39
1200UTC 09.08.2024 156 36.4N 78.5W 1001 38
0000UTC 10.08.2024 168 37.4N 76.6W 1002 36
 
The 00Z trend has been west keeping the center over land more or less the entire way up the coast.....it would be very difficult for the storm to have much of any wind field...
 
2:00 AM EDT Sat Aug 3
Location: 21.6°N 80.1°W
Moving: WNW at 17 mph
Min pressure: 1010 mb
Max sustained: 30 mph


034135_5day_cone_no_line_and_wind.png
 
0Z Euro: similar track to 12Z but stronger with it coming back into CHS at 986 mb vs 989 on 12Z; biblical rainfall amts of 20-24” mainly over ~72 hr period SAV-CHS and inland to 50 miles Lowcountry:

IMG_0053.png
 
GaWx said:
0Z Euro: similar track to 12Z but stronger with it coming back into CHS at 986 mb vs 989 on 12Z; biblical rainfall amts of 20-24” mainly over ~72 hr period SAV-CHS and inland to 50 miles Lowcountry:

View attachment 149244
Click to expand...
2ft of rain around Parris Island would be devastating. I would love the 6" here in Union County but would like to see a different solution for the SC low country.
 
The 00Z runs have some pretty big zig zags in the track from GA north....not sure what to make of the jumps in track when it gets near the SC coast, seem wonky. Its almost like the models cant decide if the storm is going to track just inland or just offshore and keep hopping back and forth between the two....though the west shift to inland is pretty evident in the last couple of cycles.
 
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Downeastnc said:
The 00Z runs have some pretty big zig zags in the track from GA north....not sure what to make of the jumps in track when it gets near the SC coast, seem wonky. Its almost like the models cant decide if the storm is going to track just inland or just offshore and keep hopping back and forth between the two....though the west shift to inland is pretty evident in the last couple of cycles.
Click to expand...
Agreed, looking back through the different models they all seem to be the same but just different specific locations. It diffidently slows around the GA/SC line and up through NC. Was a weird hour of runs.
 
I could be wrong but it seems the 0z models initialized east of where the NHC has the low centered.
 
Cliff notes: it's coming to Big Bend area and will possibly be a hurricane although we are not showing it yet as that on our map.
After that we don't have a clue. GFS says one thing and Euro another. (Been there once or twice before)

----------------

Tropical Depression Four Discussion Number 4
NWS National Hurricane Center Miami FL AL042024
500 AM EDT Sat Aug 03 2024

Small bursts of deep convection have continued near the estimated
center of the depression, with some skeletal convective bands over
the outer portions of the circulation. Earlier scatterometer data
revealed the strongest winds were occurring to the south and east of
the center, offshore of the southern coast of Cuba. The overall
organization of the tropical cyclone has changed little overnight,
and the initial intensity is held at 25 kt based on the earlier
scatterometer winds and recent Dvorak estimates from TAFB and SAB.

The estimated motion of the depression is still west-northwestward
at about 14 kt. The influence of an upper-level trough over the
eastern United States should cause the cyclone to turn northwestward
and then northward this weekend as it moves toward a break in the
subtropical ridge. This motion will bring the system across western
Cuba this morning, into the eastern Gulf of Mexico later today, and
toward the Florida Big Bend region on Sunday and Sunday night. There
is reasonably good confidence in this portion of the track forecast,
and only slight westward adjustments were made to the NHC prediction
based on the latest track consensus aids. After landfall, weakening
steering currents should cause the cyclone to slow down while it
moves northeastward over parts of northern Florida and Georgia.
Thereafter, the track forecast becomes highly uncertain as it is
unclear whether the system will accelerate northeastward ahead
of an upper trough (GFS) or get left behind and meander over
the southeastern U.S. or near the coast (ECMWF).

After the system crosses Cuba and emerges over the eastern Gulf of
Mexico, the environmental and oceanic conditions appear favorable
for intensification. The latest NHC forecast shows the cyclone
becoming a tropical storm by tonight, with additional strengthening
expected while it moves across deep warm waters in a weak shear
environment. The regional hurricane models and statistical guidance
continue to indicate some potential for the system to reach
hurricane strength before it makes landfall in the Florida Big Bend
region. Although the latest NHC forecast does not explicitly show
the cyclone becoming a hurricane, note that additional strengthening
could occur between 48-60 h. Weakening is forecast after landfall
while the system moves over the southeastern United States. Beyond
day 3, the intensity forecast remains quite uncertain and highly
dependent on whether the center stays inland or emerges off the
Atlantic coast.


Key Messages:

1. Heavy rainfall may result in locally considerable flash and urban
flooding across portions of Florida and the coastal areas of the
Southeast U.S. this weekend through Wednesday. Isolated river
flooding will also be possible.

2. A Hurricane Watch has been issued for portions of west-central
Florida and the Big Bend region, where hurricane conditions are
possible late Sunday. Tropical storm conditions are expected
farther south along Florida’s west coast, including the Tampa Bay
area, and across the Dry Tortugas where Tropical Storm Warnings are
in effect.

3. There is a possibility of life-threatening inundation from storm
surge along portions of the west coast of Florida from Bonita Beach
to Aucilla River, including Tampa Bay and Charlotte Harbor, where a
Storm Surge Watch is in effect.

4. Impacts from storm surge, strong winds, and heavy rains are
possible elsewhere in Florida and along the southeast coast of the
United States from Georgia to North Carolina through the middle of
next week, and interests in those areas should continue to monitor
the progress of this system. Additional watches and warnings will
likely be required later today.


FORECAST POSITIONS AND MAX WINDS

INIT 03/0900Z 22.0N 80.7W 25 KT 30 MPH
12H 03/1800Z 23.4N 82.6W 30 KT 35 MPH
24H 04/0600Z 25.3N 83.9W 40 KT 45 MPH
36H 04/1800Z 27.5N 84.3W 50 KT 60 MPH
48H 05/0600Z 29.1N 83.9W 60 KT 70 MPH
60H 05/1800Z 30.4N 83.1W 45 KT 50 MPH...INLAND
72H 06/0600Z 31.2N 82.2W 35 KT 40 MPH...INLAND
96H 07/0600Z 32.0N 80.5W 45 KT 50 MPH...OVER WATER
120H 08/0600Z 33.0N 79.0W 55 KT 65 MPH
 
Downeastnc said:
Big difference between the ICON and GFS....the ICON makes more sense to me as that track kinda fits historically....the big due east back due west motion the GFS shows is just weird...but tropical storms are weird sometimes.
Click to expand...
GFS is actually an improvement from 0Z as it gets a little more offshore.
 
The center this morning may be just north of the convetive blob near the caymans but visible satellite just let us know in the next hour. As we go through the day into tonight this should start getting some outflow help from the right entrance to the jet along the EC, this may help it some convectively as well. It'll be interesting to see what this looks like around this time tomorrow as it's in a much better environment and away from Cuba. The track after the first landfall in Florida is nightmare fuel. You can make a case for a steady N to NNE motion as easy as you can the hard right, stall, hard left track.
 
It might be the NAM but it was much further W than all the previous runs, taking it now into S central GA vs the coast. If it remains at 12Z we'll have to see how the other models follow but if we aren't seen that N component as much as expected now, it's not going into the Atlantic how its currently modeled
 
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