ATL: LAURA - Post-Tropical - Discussion

[supercane4867]

There’s a decent chance that it may intensify until landfall or very close to landfall.

[Hypercane_Kyle]

I see a lot of posts (and I've been guilty of this myself, especially while Laura was dodging mountains) looking at 1-2 hour trends in motion as "this should help it avoid island x" or "this puts city y more in play". Let's keep in mind that the 6-hour average motion is what matters at this point. Laura is going to stair step its way to the Gulf coast.

[SouthernBreeze]

from Disco -

FORECAST POSITIONS AND MAX WINDS

INIT 25/1500Z 23.7N 87.0W 65 KT 75 MPH
12H 26/0000Z 24.6N 89.2W 75 KT 85 MPH
24H 26/1200Z 26.0N 91.5W 90 KT 105 MPH
36H 27/0000Z 28.0N 93.3W 100 KT 115 MPH
48H 27/1200Z 30.5N 93.9W 80 KT 90 MPH...INLAND
60H 28/0000Z 33.1N 93.6W 45 KT 50 MPH...INLAND
72H 28/1200Z 35.2N 92.1W 30 KT 35 MPH...INLAND
96H 29/1200Z 37.5N 83.5W 25 KT 30 MPH...INLAND
120H 30/1200Z 40.5N 69.5W 40 KT 45 MPH...POST-TROP/EXTRATROP

[Blinhart]

Is the cone staying the same since they are expecting it to be strengthening all the way in, and most strong systems have a more poleward movement, so it might actually make a turn earlier than the models are showing. We always usually see landfalling systems here in the Tx/La area make landfall a little to the East of where the models show, so they are taking historical tracks into consideration for this cone??

[plasticup]

The cone remains nearly the same. Houston/Galveston are on the western edge of the cone.

And the cone is east of the model guidance:

[NHC forecast track] still lies a little east of the consensus models at the time of landfall

[Chris_in_Tampa]

https://twitter.com/TheSteveCop/status/1298263639917395969/photo/1

I believe this data is inaccurate in my system. I have made a correction to the vortex message. I believe they accidentally coded a value as 76kts when it was actually 76mph.

[Shell Mound]

https://i.imgur.com/hv5o9IA.jpg

That’s about as good upper level setup as you see with cyclones. Upper-level high centered over the center with strong upper-level winds to the north for ventilation.

Actually, outflow to the north is still quite restricted. Note that net shear from the north persists, due to Laura’s background movement and mid-level winds. Only the southern quadrant features a well-defined outflow jet, thanks to the retrograding TUTT on Laura’s eastern flank. Laura still needs to approach the cutoff low over Texas before a poleward outflow channel can develop. If not for the remnants of Marco, Laura would likely be intensifying faster now, but the large inner core is also impeding the rate of intensification. As for the track, I definitely agree that some of the models have a westward bias with Gulf cyclones curving northward into the westerlies. Additionally, note this excerpt from the NHC’s latest discussion, which limits the time Laura has for deepening:

Conditions appear generally favorable for strengthening during the next 36 h, and the new intensity forecast calls for Laura to become a major hurricane during this
time. The global model are in good agreement that the hurricane should encounter increasing shear in the last 12 h before landfall, although the potential impacts on the landfall intensity are unclear.

[ATCcane]

Seems like the Air Force birds are constantly having com issues on missions. Untimely this morning for sure.

[Beef Stew]

Is the cone staying the same since they are expecting it to be strengthening all the way in, and most strong systems have a more poleward movement, so it might actually make a turn earlier than the models are showing. We always usually see landfalling systems here in the Tx/La area make landfall a little to the East of where the models show, so they are taking historical tracks into consideration for this cone??

As per the discussion:

"The new forecast track before landfall has been nudged a little to the west of the previous track in response to a westward nudge in the guidance. However, it still lies a little east of the consensus models at the time of landfall."

It's not specified as to why, but it could be that they are giving some weight to the poleward movement of a stronger storm. They could also be waiting on more samples from the ridge.

[cycloneye]

The 11 AM track at landfall.

[FLpanhandle91]

Looks to me like northerly shear and subsequent dry air entrainment had limited Laura's intensification this morning. I'm sure that will change though.

[cheezyWXguy]

Is the cone staying the same since they are expecting it to be strengthening all the way in, and most strong systems have a more poleward movement, so it might actually make a turn earlier than the models are showing. We always usually see landfalling systems here in the Tx/La area make landfall a little to the East of where the models show, so they are taking historical tracks into consideration for this cone??

As per the discussion:

"The new forecast track before landfall has been nudged a little to the west of the previous track in response to a westward nudge in the guidance. However, it still lies a little east of the consensus models at the time of landfall."

It's not specified why, but it could be that they are giving some weight to the poleward movement of a stronger storm. They could also be waiting on more samples from the ridge.

I thought in this case it would be steered more west if stronger, because the upper level steering will have more influence.

[Blinhart]

The 11 AM track at landfall.

https://i.imgur.com/kgZLhEV.jpg

I just know that this puts me in the NE quadrant, and we are now under both a Hurricane Warning and a Storm Surge Warning. So it is going to be an interesting 48 hours coming.

[Highteeld]

Based on satellite, intensification may have halted in the short term

[MBryant]

I had to check in one more time. I'm still on a desktop, so I can't log in after I leave. I'm hoping for the best (weaker than anticipated) and preparing for the worst. But I'm 2 miles west of the Sabine and <half a mile north of I-10.

[Hybridstorm_November2001]

If there is any slight sliver lining here it is the relatively high speed at which Laura is traveling. Her forward speed just might prove to be a limiting factor regarding overall intensity. Don't get me wrong, Laura will still likely be a major hurricane at landfall but her good clip might prove the difference between a cat 3 rather than a high end cat 4 or even a cat 5 hitting the coast.

[GCANE]

Definitely entraining stable air.
CAPE dropping in the core.

[Blinhart]

If there is any slight sliver lining here it is the relatively high speed at which Laura is traveling. Her forward speed just might prove to be a limiting factor regarding overall intensity. Don't get me wrong, Laura will still likely be a major hurricane at landfall but her good clip might prove the difference between a cat 3 rather than a high end cat 4 or even a cat 5 hitting the coast.

16 MPH isn't that quick, she can easily get to Cat 4.

[mpic]

Immediate mandatory evac of Galveston Island has been issued. This will be a nightmare on the roads.

[stormwatcher95]

HURRICANE 13L 12:00UTC 25August2020
UW-CIMSS Experimental Vertical Shear and TC Intensity Trend Estimates

Current Conditions (from NHC) :
Latitude : 23:21:06 N
Longitude : 86:46:43 W
Intensity (MSLP) : 987.0 hPa

Max Pot Int (MPI,from Emanuel) : 890.0 hPa
MPI differential (MSLP-MPI) : 97.0 hPa

CIMSS Vertical Shear Magnitude : 1.3 m/s ( 2.5 kts)
Direction : 268.9 deg

Outlook for TC Intensification Based on Current
Env. Shear Values and MPI Differential
Forecast Interval : 6hr 12hr 18hr 24hr
VF VF VF VF

Legend : VF-Very Favorable F-Favorable N-Neutral
U-Unfavorable VU-Very Unfavorable

-- Mean Intensity Trend (negative indicates TC deepening) --
6hr 12hr 18hr 24hr
VF <-3.0mb/ 6hr <-6.0mb/12hr <-9.0mb/18hr <-12.0mb/24hr
F -3.0 - -1.0 -6.0 - -2.0 -9.0 - -3.0 -12.0 - -4.0
N -1.0 - +1.0 -2.0 - +2.0 -3.0 - +3.0 -4.0 - +4.0
U +1.0 - +3.0 +2.0 - +6.0 +3.0 - +9.0 +4.0 -+12.0
VU >+3.0 >+6.0 >+9.0 >+12.0