ATL: HELENE - Post-Tropical - Discussion

[cycloneye]

8 AM: PTC at 11 AM EDT.

Northwestern Caribbean Sea and Gulf of Mexico (AL97):
Showers and thunderstorms are gradually becoming better organized in
association with a broad area of low pressure located over the
northwestern Caribbean Sea. Environmental conditions appear
favorable for further development of this system. A tropical
depression or storm is likely to form within the next day or two as
the system moves northward across the northwestern Caribbean Sea and
into the southeastern Gulf of Mexico, where additional development
is expected.

1. Regardless of development, this system is expected to produce heavy
rains over portions of Central America during the next several days.
Interests in the northwestern Caribbean, the Yucatan Peninsula of
Mexico, and western Cuba should closely monitor the progress of this
system, as watches or warnings will likely be required later
this morning for portions of these areas. Later this week, the
system is forecast to move generally northward across the eastern
Gulf of Mexico, and interests along the northern and northeastern
Gulf Coast should also closely monitor the progress of this system.
* Formation chance through 48 hours...high...80 percent.
* Formation chance through 7 days...high...90 percent.

[Stormlover70]

For now, I have landfall northern Apalachee Bay Thursday afternoon. Moving north at 20 kts at landfall. Lots of SW shear across northern Gulf. Initial forecast has 75 kts at landfall. Large wind field, particularly east of the center. Could produce tides 5-10 ft into Tampa - higher if the track shifts any east.

finally the voice of reason. Welcome back. I hope you enjoyed your time off
Albeit a few days.

[ouragans]

Interests in the northwestern Caribbean, the Yucatan Peninsula of Mexico, and western Cuba should closely monitor the progress of this system, as watches or warnings will likely be required later this morning for portions of these areas.

We should have a PTC at 15z

[Hypercane_Kyle]

Either outflow from TS John or displacement of the ULAC appears to be causing 97L to form more east than expected. This is why the GFS/Euro has shifted east. Tampa needs to be on alert for these trends to continue.

[GCANE]

Looking at the latest GFS, once this passes the Yucatan Channel it will be under a minor ARWB created by the trof.
Looks like it will be able to strengthen during a good portion of its trek in the GoM due to the ARWB and a very strong high TPW feed from the EPAC.
Shear will pickup as it closes into the trof and landfall.

[aspen]

Either outflow from TS John or displacement of the ULAC appears to be causing 97L to form more east than expected. This is why the GFS/Euro has shifted east. Tampa needs to be on alert for these trends to continue.

I’m willing to bet it’s from John, because the HWRF-P 200mb flow does show a little bit of John’s outflow intersecting 97L/Helene at some point during the next 2 days.

[xironman]

Either outflow from TS John or displacement of the ULAC appears to be causing 97L to form more east than expected. This is why the GFS/Euro has shifted east. Tampa needs to be on alert for these trends to continue.

I’m willing to bet it’s from John, because the HWRF-P 200mb flow does show a little bit of John’s outflow intersecting 97L/Helene at some point during the next 2 days.

The upper trough over the Yucatan channel is probably contributing to.

[wxman57]

For now, I have landfall northern Apalachee Bay Thursday afternoon. Moving north at 20 kts at landfall. Lots of SW shear across northern Gulf. Initial forecast has 75 kts at landfall. Large wind field, particularly east of the center. Could produce tides 5-10 ft into Tampa - higher if the track shifts any east.

finally the voice of reason. Welcome back. I hope you enjoyed your time off
Albeit a few days.

Yes, I enjoyed the last 4 days off.

Note that large upper-level low positioned over Arkansas this week. That's why all the models are in very good agreement on an east FL Panhandle hit. Very strong SW wind aloft across central to northern Gulf should cause most strong wind and squalls to be positioned east of the track. Watch out west coast of FL Peninsula.

[chris_fit]

@WXMAN57 - Thoughts on Tampa Area for severe impacts? Should we be worried here? I know you've said many times "they always go right of track" - Is the setup the same where this would apply? (Charley, Ian, Irma) or is this more of an Idalia event where I believe it went a little West of track?

[underthwx]

For now, I have landfall northern Apalachee Bay Thursday afternoon. Moving north at 20 kts at landfall. Lots of SW shear across northern Gulf. Initial forecast has 75 kts at landfall. Large wind field, particularly east of the center. Could produce tides 5-10 ft into Tampa - higher if the track shifts any east.

finally the voice of reason. Welcome back. I hope you enjoyed your time off
Albeit a few days.

Yes, I enjoyed the last 4 days off.

Note that large upper-level low positioned over Arkansas this week. That's why all the models are in very good agreement on an east FL Panhandle hit. Very strong SW wind aloft across central to northern Gulf should cause most strong wind and squalls to be positioned east of the track. Watch out west coast of FL Peninsula.

Good morning Xman....the low you mention over Arkanasas....is 97L actually going to keep that low positioned where it is?....if I understand this correctly...the low over Arkansas is the main force that is pulling 97L Northward?.....i read this excerpt from Houston/Galveston forecast discussion..."The upper level pattern gets a bit messy by the end of the week.
That closed low that stalls over the Mississippi Valley ends up
retrograding back westward Friday and into the weekend. This is due
to a tropical system (currently Invest 97L in the western Caribbean,
but likely a named tropical system by midweek) moving through the
eastern Gulf of Mexico effectively blocking the movement of the
upper level low. So, as this system moves back westward, so does the
moisture associated with it. The wrap around moisture may bring
scattered showers and storms to our area Friday into the weekend -
but confidence is not exactly high as it will be determined where
exactly the upper level low retrogrades to and how it interacts with
the tropical system. That upper level low ends up sticking around
through much of the weekend before finally moving off east late
Sunday into Monday".....is this the low you mention?.....many thanks...

[Blown Away]

Some bubbling occurring near the rotation @17N/80.5W…

[StPeteMike]

[url]https://i.postimg.cc/V66SGtYW/goes16-vis-swir-97-L-202409230925.gif [/url]

Some bubbling occurring near the rotation @17N/80.5W…

Yep! She’ll likely fill herself in with convection the rest of the morning and afternoon. We shall see what she looks like around 1700 eastern.

[DunedinDave]

[url]https://i.postimg.cc/V66SGtYW/goes16-vis-swir-97-L-202409230925.gif [/url]

Some bubbling occurring near the rotation @17N/80.5W…

Definitely a spin there. Wow that’s way east. Kudos to GFS…they caught on to that and factored it into their latest model run (hence the east shift).

[wxman57]

The ICON has done very well with Gulf storms this year. The main steering factor will be a large and strong upper-level low over Arkansas. This will keep "Helene" out of the NW Gulf. As for questions about Tampa - yes, there is a better chance of the storm tracking closer to Tampa. As it stands now, we're looking at a 5-8 ft surge into Tampa, even with the storm passing well to the west. The 20kt northerly forward speed across the NE Gulf is a testament to the well-established steering flow.

https://www.tropicaltidbits.com/analysis/models/icon/2024092306/icon_z500_vort_watl_30.png

[psyclone]

That's a very vigorous spin. This thing is going to take off soon and fast. PTC designation won't be needed long on this one. This current look reminds me of Ian before it went nuts. Let's hope this one under shoots that one by a lot. Very surge prone coast around Tampa bay. I'm right at the top of the bay...thankfully on high ground but close to very vulnerable areas.

[cycloneye]

 https://x.com/AndyHazelton/status/1838189397209948528

[boca]

[url]https://i.postimg.cc/V66SGtYW/goes16-vis-swir-97-L-202409230925.gif [/url]

Some bubbling occurring near the rotation @17N/80.5W…

If that becomes the center the SE coast of Florida might be getting alittle more action than just rain showers .

[underthwx]

That's a very vigorous spin. This thing is going to take off soon and fast. PTC designation won't be needed long on this one. This current look reminds me of Ian before it went nuts. Let's hope this one under shoots that one by a lot. Very surge prone coast around Tampa bay. I'm right at the top of the bay...thankfully on high ground but close to very vulnerable areas.

I wish you...and all yall in potential impact areas...the best....this is shaping up to be an event that will affect millions along the coast of Florida and points northward.....lets get this system outta here quickly....

[WaveBreaking]

Convection firing closer to the vortmax.

[cycloneye]

12z Best Track:

AL, 97, 2024092312, , BEST, 0, 172N, 818W, 25, 1004, DB