ATL: LAURA - Post-Tropical - Discussion

[jconsor]

Still watching for track shifts SW of most guidance (closer to 12Z EPS), given upper air developments so far this morning.

 https://twitter.com/yconsor/status/1298577283796602880

[jconsor]

My thoughts on potential Houston metro area and Galveston impacts:

 https://twitter.com/yconsor/status/1298582554862333954

[Kingarabian]

Looking at the Euro and the GFS, they show strong SW upper level winds probably associated with the jet as well as the trough that will steer it close to the TX/LA border. If this shear does not weaken the system, these winds could end up pushing strong effects well in land further away from the center. Very tricky storm.

[tolakram]

Water Vapor loop showing upper level conditions.

https://weather.cod.edu/satrad/?parms=continental-southconus-08-200-1-100-1&checked=map&colorbar=undefined

[Kingarabian]

ADT and Recon estimates continue to be on the same page in terms of pressure:

2020AUG26 110000 5.1 961.8 92.4 5.1 5.8 6.9 1.7T/6hr OFF OFF -26.66 -75.63 EYE 12 IR 10.6 26.25 91.25 COMBO GOES16 35.6

[NDG]

I believe CAPE values are high enough for Laura to maintain an annular structure. She's going to bottom out at MPI

What is "MPI"?

Maximum Potential Intensity
https://i.imgur.com/dy5tHjY.png

30C SSTs all the way to the coast is more than enough to maintain its strengthening even if it was to be shallow warm waters, is moving fast enough.

[Shell Mound]

The fact that the ECMWF/GFS are underestimating the meridional extent of the mid-level ridge also implies that there will be less westerly shear, given that Laura is less likely to turn NNW and N—that is, encounter higher net VWS—until several hours after landfall. That is why the 06Z HMON/HWRF output shows Laura being steady state or even intensifying slightly at the time of landfall. Unfortunately, this means that a borderline Category-4/-5 hurricane is becoming increasingly likely at the time of landfall near the TX/LA border. Note that the HMON/HWRF also handled Michael and Dorian far better than most of the other guidance in terms of intensity.

[supercane4867]

Equatorial outflow channel is still very pronounced at the time of landfall on 06z HWRF run. Very unlikely that there will be any weakening prior to landfall. Both HMON and HWRF are showing an intensifying at landfall scenario.

[hurricaneCW]

Unless the shear is very strong it'll have limited effects on a very large major hurricane. An EWRC is much more likely to cause the storm to weaken prior to landfall.

[USTropics]

100 frames saved (large file, may take a few to load). The frequency of gravity waves emitting from the center of Laura almost give this an optical illusion effect:

[Kingarabian]

Looks like the NOAA plane is about to do a SW-NE pass.

[NotoSans]

Given current trends I think NHC needs a special advisory to revise short-term intensity forecast.

[supercane4867]

Center dropsonde 964mb with 8kt winds. A significant drop since the last fix by the AF plane(969mb)

[Kingarabian]

What is "MPI"?

Maximum Potential Intensity
https://i.imgur.com/dy5tHjY.png

30C SSTs all the way to the coast is more than enough to maintain its strengthening even if it was to be shallow warm waters, is moving fast enough.

And all those "Marco's cold wake may affect Laura" comments on social media don't look too good right now. The GOM waters are something else.

[Kazmit]

I am in absolute shock of what I just woke up to.

[HurricaneEnzo]

Dual outflow channels, anti-cyclone overhead, bathtub warm waters, and moist air. Nothing about this setup inspires any kind of hopefulness tbh.

[p1nheadlarry]

Serious question, what's stopping it from bottoming out? There's some shear near the coast but that's about it

MPI has ~920-930 in this region, but IIRC that only takes into account SST and not themocline depth which is also important, though maybe not as much with its brisk movement. Also I'm not sure how it takes into account the 'exhaust' temperature which is in theory as far from the center as possible, and also environmental pressure. So shear as it approaches land and some reorganization could limit it's peak intensity, but note the HWRF and other models have brought Laura to ~940 so not terribly far off.

[BensonTCwatcher]

Pressure drops coming in are just scary, In looking at HWRF and Euro runs, they are showing pressures in the 930-937mb range at landfall. Not really far to go at this rate to surpass that. I would add though that we are getting into the areas where few storms can go. Even though we have the conditions, it's still rare overall to get this kind of intensity. It could very well be that Laura is heading to peak intensity now and that would be good news in that we could see weakening due to structural issues on the final approach to land. Having been in many hurricanes and some tyhpoons, the actual intensity and ferocity seen is quite different in a storm strengthening on impact. Need a bit of luck over the next few hours.

[Shell Mound]

Top five strongest Louisiana landfalling hurricanes, 1851–2019*

1. 1856 #1 – 130 knots – “Last Island”
2. 1893 #10 – 115 knots – “Chenière Caminada”
3. 1965 Betsy – 115 knots
4. 1855 #5 – 110 knots – “Middle Gulf Shore”
5. 1860 #1 – 110 knots

*Sorted by maximum sustained wind speed

Technically, Camille (1969) did not make landfall in LA, but produced Cat-5 conditions near the MS Delta.

[Jr0d]

Given current trends I think NHC needs a special advisory to revise short-term intensity forecast.

The intermediate advisory is due any minute. They can make that change with it.