ATL: HELENE - Post-Tropical - Discussion

[Steve]

POTENTIAL TROP CYCLONE CENTER LOCATED NEAR 17.6N 82.0W AT 23/1500Z
POSITION ACCURATE WITHIN 45 NM

PRESENT MOVEMENT TOWARD THE NORTH OR 350 DEGREES AT 5 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 1004 MB
MAX SUSTAINED WINDS 25 KT WITH GUSTS TO 35 KT.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT...CENTER LOCATED NEAR 17.6N 82.0W AT 23/1500Z
AT 23/1200Z CENTER WAS LOCATED NEAR 17.2N 81.8W

FORECAST VALID 24/0000Z 18.6N 82.4W...TROPICAL CYCLONE
MAX WIND 30 KT...GUSTS 40 KT.

FORECAST VALID 24/1200Z 19.5N 83.7W
MAX WIND 40 KT...GUSTS 50 KT.
34 KT...120NE 120SE 0SW 0NW.

FORECAST VALID 25/0000Z 20.6N 85.1W
MAX WIND 50 KT...GUSTS 60 KT.
50 KT... 40NE 20SE 0SW 0NW.
34 KT...170NE 150SE 70SW 100NW.

FORECAST VALID 25/1200Z 22.1N 86.0W
MAX WIND 65 KT...GUSTS 80 KT.
64 KT... 20NE 20SE 0SW 0NW.
50 KT... 60NE 50SE 40SW 40NW.
34 KT...200NE 190SE 100SW 130NW.

FORECAST VALID 26/0000Z 24.2N 86.0W
MAX WIND 85 KT...GUSTS 105 KT.
50 KT... 90NE 90SE 50SW 60NW.
34 KT...220NE 210SE 130SW 160NW.

FORECAST VALID 26/1200Z 27.1N 85.1W
MAX WIND 95 KT...GUSTS 115 KT.
50 KT...100NE 110SE 60SW 60NW.
34 KT...220NE 220SE 150SW 150NW.

EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 125 NM
ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY

OUTLOOK VALID 27/1200Z 34.0N 83.0W...INLAND
MAX WIND 35 KT...GUSTS 45 KT.
34 KT... 0NE 180SE 0SW 0NW.

OUTLOOK VALID 28/1200Z 38.5N 87.0W...POST-TROPICAL
MAX WIND 20 KT...GUSTS 30 KT.

REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 17.6N 82.0W

INTERMEDIATE PUBLIC ADVISORY...WTNT34 KNHC/MIATCPAT4...AT 23/1800Z

NEXT ADVISORY AT 23/2100Z

$$
FORECASTER REINHART

[fllawyer]

000
WTNT44 KNHC 231500
TCDAT4

Potential Tropical Cyclone Nine Discussion Number 1
NWS National Hurricane Center Miami FL AL092024
1100 AM EDT Mon Sep 23 2024

A broad area of low pressure over the northwestern Caribbean Sea
continues to produce disorganized showers and thunderstorms. While
some mid-level rotation is evident in visible satellite images,
surface observations and visible satellite images suggest the
low-level circulation remains broad and farther to the southwest.
Nonetheless, the system has a high chance of tropical cyclone
formation during the next day or two, and it is likely to bring
tropical storm conditions to land areas within the next 36 to
48 hours. Therefore, the NHC is initiating Potential Tropical
Cyclone advisories for this disturbance.

The initial motion is quite uncertain given the current lack of
organization, but the best estimate is northward at about 5 kt. A
gradual turn toward the northwest is expected during the next day or
so, with the center passing through the Yucatan Channel and into the
southern Gulf of Mexico. Thereafter, the system is forecast to
accelerate northward across the eastern Gulf of Mexico within the
flow between a digging deep-layer trough over the central United
States and a ridge over the western Atlantic. This motion should
bring the center of the system toward the northeastern Gulf Coast on
Thursday. The track guidance agrees reasonably well on this
scenario, and the initial NHC forecast lies near the simple and
corrected consensus aids. Since the disturbance currently lacks a
well-defined center, users are reminded that the average forecast
track uncertainty is larger in these situations, and future track
adjustments may be required. Given the large size of the
tropical-storm-force wind field and fast forward speed that is
forecast, storm surge, wind, and rainfall impacts will likely extend
well away from the center, particularly to the east of the system.

While the system is currently broad and not well organized, the
models suggest a more well-defined center should develop during the
next day or so. Once the system becomes better organized and
develops an inner core, the environmental and oceanic conditions
appear favorable for significant strengthening. In fact, the DTOPS
statistical guidance shows a 95 percent chance of a 65-kt increase
in intensity during the next 72 h, and the hurricane regional models
highlight the potential for strengthening to major hurricane
intensity. Thus, the NHC forecast shows significant strengthening
while the system moves across the eastern Gulf of Mexico, with a
95-kt intensity in 72 h. While this forecast is aggressive, it lies
near or slightly below the consensus aids, and future adjustments
may be necessary. An Air Force Reserve reconnaissance aircraft is
scheduled to investigate the system this afternoon.

Based on the NHC forecast, Tropical Storm Warnings and Hurricane
Watches have been issued for portions of western Cuba the Yucatan
Peninsula of Mexico. Interests along the northeastern Gulf Coast,
including the Florida Panhandle and portions of the Florida west
coast should monitor the progress of this system.


KEY MESSAGES:

1. The disturbance is forecast to strengthen and be near hurricane
strength when it reaches the far northwestern Caribbean Sea Tuesday
night. Tropical storm conditions are expected over portions of
western Cuba and the northeastern coast of the Yucatan Peninsula
with hurricane conditions possible.

2. The system is expected to intensify while it moves northward
over the eastern Gulf of Mexico, and it could be a major hurricane
when it reaches the northeastern Gulf Coast on Thursday. There is an
increasing risk of life-threatening storm surge and damaging
hurricane-force winds along portions of the northern and
northeastern Gulf Coast, including the Florida Panhandle and
portions of the Florida west coast. Although it is too soon to
specify the exact location and magnitude of impacts, residents in
these areas should monitor the latest forecast updates and ensure
that they have their hurricane plan in place.

3. Potential Tropical Cyclone Nine will bring heavy rain to portions
of the western Caribbean which may lead to flooding and possible
mudslides in western Cuba.


FORECAST POSITIONS AND MAX WINDS

INIT 23/1500Z 17.6N 82.0W 25 KT 30 MPH...POTENTIAL TROP CYCLONE
12H 24/0000Z 18.6N 82.4W 30 KT 35 MPH...TROPICAL CYCLONE
24H 24/1200Z 19.5N 83.7W 40 KT 45 MPH
36H 25/0000Z 20.6N 85.1W 50 KT 60 MPH
48H 25/1200Z 22.1N 86.0W 65 KT 75 MPH
60H 26/0000Z 24.2N 86.0W 85 KT 100 MPH
72H 26/1200Z 27.1N 85.1W 95 KT 110 MPH
96H 27/1200Z 34.0N 83.0W 35 KT 40 MPH...INLAND
120H 28/1200Z 38.5N 87.0W 20 KT 25 MPH...POST-TROPICAL

$$
Forecaster Reinhart

[Steve]

95. Yikes.

[Beef Stew]

INIT 23/1500Z 17.6N 82.0W 25 KT 30 MPH...POTENTIAL TROP CYCLONE
12H 24/0000Z 18.6N 82.4W 30 KT 35 MPH...TROPICAL CYCLONE
24H 24/1200Z 19.5N 83.7W 40 KT 45 MPH
36H 25/0000Z 20.6N 85.1W 50 KT 60 MPH
48H 25/1200Z 22.1N 86.0W 65 KT 75 MPH
60H 26/0000Z 24.2N 86.0W 85 KT 100 MPH
72H 26/1200Z 27.1N 85.1W 95 KT 110 MPH
96H 27/1200Z 34.0N 83.0W 35 KT 40 MPH...INLAND
120H 28/1200Z 38.5N 87.0W 20 KT 25 MPH...POST-TROPICAL


Wow... already a peak intensity estimate of 110 mph. That's quite rare for a first NHC forecast, and I suspect it will rise once the center actually consolidates.

[USTropics]

There will be some westward component to motion later today and tomorrow. I've outlined the main synoptic 'players' that will dictate our steering flow:

(1) Highlighted in pink is our shortwave trough that is digging, which is where our cutoff low will originate later today and dive southeastward (pink dashed)
(2) This will reinforce the front (green dashed) currently over the central CONUS
(3) When this initially occurs, it will begin to displace a narrow 500mb ridge (orange) currently over the GOM
(4) This will begin to block the influence of the troughing (teal) over the north Atlantic, and induce the westward component to motion





The key here is, where does the center form and how gradual of a shift west is there (red lines)? That launching point later on when the storm begins to interact with the cutoff low/trough over the central CONUS will be important to eventual landfall locations.

[Poonwalker]

I see it at 18.2N 81.8W. Still a sheared and tilted system to the SE as expected. There has been some reduction in shear the last six hours but it has to get to the Yucatan before conditions are very favorable. That might happen tomorrow. GFS has had the best handle on this one.

[Steve]

I see it at 18.2N 81.7W

The initiated it a bit SW of that location.

[Pipelines182]

I really really hate the way the NHC issues these intensity forecasts. I think their estimate is fine, but they really need to do a better job of broadcasting the ceiling on this storm is significantly higher than 95kt. Most people don't read anymore except for headlines, all they're going to see is "forecast to make landfall as a cat 2". When in reality they need to be seeing "forecast to make landfall anywhere from Cat 2 - 4".

[psyclone]

They're keeping that track well to the west. I feel a helluva lot better here seeing that. I just want some porch sitting squalls, cocktails and bong hauls...keep that core offshore. I was fearful of a Levy or Dixie county landfall estimate taking the center much closer to the FL west coast..

[Hypercane_Kyle]

They're keeping that track well to the west. I feel a helluva lot better here seeing that. I just want some porch sitting squalls, cocktails and bong hauls...keep that core offshore. I was fearful of a Levy or Dixie county landfall estimate taking the center much closer to the FL west coast..

If you read the discussion, they are not confident in that track at all.

[DunedinDave]

They're keeping that track well to the west. I feel a helluva lot better here seeing that. I just want some porch sitting squalls, cocktails and bong hauls...keep that core offshore. I was fearful of a Levy or Dixie county landfall estimate taking the center much closer to the FL west coast..

If the center forms to the east of where they have it, you gotta shift everything about a degree to the right. They basically said straight up they’re not sure about where the center is.

[AutoPenalti]

They're keeping that track well to the west. I feel a helluva lot better here seeing that. I just want some porch sitting squalls, cocktails and bong hauls...keep that core offshore. I was fearful of a Levy or Dixie county landfall estimate taking the center much closer to the FL west coast..

Always good to read the forecast discussion...

This motion should bring the center of the system toward the northeastern Gulf Coast on
Thursday. The track guidance agrees reasonably well on this
scenario, and the initial NHC forecast lies near the simple and
corrected consensus aids. Since the disturbance currently lacks a
well-defined center, users are reminded that the average forecast
track uncertainty is larger in these situations, and future track
adjustments may be required. Given the large size of the
tropical-storm-force wind field and fast forward speed that is
forecast, storm surge, wind, and rainfall impacts will likely extend
well away from the center, particularly to the east of the system.

[psyclone]

They're keeping that track well to the west. I feel a helluva lot better here seeing that. I just want some porch sitting squalls, cocktails and bong hauls...keep that core offshore. I was fearful of a Levy or Dixie county landfall estimate taking the center much closer to the FL west coast..

If you read the discussion, they are not confident in that track at all.

I did and first tracks are gambles...and the wind probs are aggressive...but in a search for any good news that is significant. a couple degrees longitude gives us more play than I anticipated. Of course someone is going to get creamed most likely

[underthwx]

95. Yikes.

This cyclone means business....everyone in the predicted affected areas need to calmly begin preparations today....be safe....take care of each other....

[Hypercane_Kyle]

They're keeping that track well to the west. I feel a helluva lot better here seeing that. I just want some porch sitting squalls, cocktails and bong hauls...keep that core offshore. I was fearful of a Levy or Dixie county landfall estimate taking the center much closer to the FL west coast..

If you read the discussion, they are not confident in that track at all.

I did and first tracks are gambles...and the wind probs are aggressive...but in a search for any good news that is significant. a couple degrees longitude gives us more play than I anticipated. Of course someone is going to get creamed most likely

Not too sure if it's even that significant. Maybe if it were a developed tropical depression, I'd agree - but the trends east are real, and this system has not developed a LLC yet.

Not trying to dampen your outlook at all, just be careful planning for sitting on the porch sipping cocktails plan, I know you've seen sometimes this can turn out very differently.

[cycloneye]

 https://x.com/JimCantore/status/1838236827729236250

@JimCantore
NHC issues first track cone for #PTC9. NHC has stated their top end wind speeds is not as aggressive as some of the guidance. Regardless, once an inner core is established, nothing will stop a very likely rapid intensification. So by this time Wednesday, we are looking at a whole different animal. Areas inside and outside of the track cone need to prepare for storm surge, rainfall, strong and damaging winds. Over the weekend the timeline for this event has sped up rapidly, and preparations should begin now.

[Pipelines182]

Anyone else notice that low over 55W 32.5N? Sure looks warm core to me, and possibly a closed circulation. Could steal that H name and give nine the dreaded I....

[Hypercane_Kyle]

Recon will be highly beneficial when it gets here soon. If we can see under-the-hood where this LLC is setting up, I'd have more confidence in a Perry, FL scenario vs further east/south.

[Kazmit]

I really really hate the way the NHC issues these intensity forecasts. I think their estimate is fine, but they really need to do a better job of broadcasting the ceiling on this storm is significantly higher than 95kt. Most people don't read anymore except for headlines, all they're going to see is "forecast to make landfall as a cat 2". When in reality they need to be seeing "forecast to make landfall anywhere from Cat 2 - 4".

Anyone who doesn't take a high-end cat 2 seriously has only themselves to blame. Plus, they do state in their discussion: "While this forecast is aggressive, it lies near or slightly below the consensus aids, and future adjustments may be necessary."

[Ken711]

Ryan Maue
@RyanMaue
·
9m
⚠️Everyone can see the weather model output for 09L (Helene) and it doesn't look good for the Florida Gulf Coast.

Worst case scenario is Category 5 -- and there's really nothing stopping this tropical system from maxing out.

Impacts well inland as well

Ryan Maue
@RyanMaue
·
31m
NHC won't explicitly put a major hurricane on the cone, at the outset. 95 knots as per previous storms, and that has served the forecast advisory process well.