ATL: MARCO - Remnants - Discussion

[Shell Mound]

This thing will be dead by tomorrow afternoon the rate it’s decaying... bones get ready

All I know is that this looks more like a borderline TD/TS than a borderline hurricane at the moment.

[wx98]

Looks like the whole thing is getting blown toward Mobile and Pensacola. The LLC is trying to start its turn toward Louisiana tonight.

[wx98]

Slowly reducing the winds now:

1:00 AM CDT Mon Aug 24
Location: 27.2°N 87.9°W
Moving: NNW at 12 mph
Min pressure: 1002 mb
Max sustained: 65 mph

[USTropics]

Can just make out some vorticity on the SW fringe of the canopy as it becomes sheared off towards the NE. Hard to to tell if that's just the MLC and the LLC is a bit further south though.

[jconsor]

 https://twitter.com/yconsor/status/1297820137719058433

[wxman57]

I'm curious as to how a small, naked swirl of low clouds with very little wind fetch will produce a large storm surge.

[xironman]

I had been waiting for KOVA https://www.ndbc.noaa.gov/station_page.php?station=kvoa to show a south component. But it is still stuck at 90 degrees.

[GCANE]

A tongue of rapidly deepening high CAPE air is entraining into Marco's core.
Maybe Marco makes one more burst before the coast.
He sure likes to catch many by surprise.

[GCANE]

Also, there is some helicity with the convection to the NE.
May see a couple waterspouts move on shore.






Mesoscale Discussion 1557
NWS Storm Prediction Center Norman OK
0146 AM CDT Mon Aug 24 2020

Areas affected...portions of the FL Panhandle

Concerning...Severe potential...Watch unlikely

Valid 240646Z - 240915Z

Probability of Watch Issuance...20 percent

SUMMARY...A waterspout could impact beaches from Franklin County
toward Walton County over the next few hours. However, the tornado
threat should remain low inland, away from the immediate coast.

DISCUSSION...A band of thunderstorms associated with an area of low
level confluence on the eastern periphery of Tropical Storm Marco
has persisted for several hours. Areas of low level rotation have
been noted in velocity data from KTLH. VWP data shows enlarged low
level hodographs with 0-1 km SRH values from around 100-200 m2/s2.
However, east/northeasterly low level flow is maintaining generally
low 70s F dewpoints across the region for now. This is limiting
surface-based instability, with SBCAPE values as high as 1000 J/kg
possible near the immediate coast, per modified 06z TLH sounding.
While a waterspout moving onshore cannot be ruled out, the
expectation is that any tornado activity will be confined to the
immediate coast and generally be weak and short-lived. As convection
moves inland, conditions will quickly become less favorable for
maintenance of low level rotation and tornado activity in the
absence of deep/richer low level dewpoints. Trends will continue to
be monitored, but a tornado watch does not appear necessary at this
time.

..Leitman/Thompson.. 08/24/2020

[wxman57]

I can't really find a center with IR imagery. I think it may be near the red crosshairs, if there is one. Appears to be a remnant low with maybe 25 kt winds. Pressure may be 1008-1009mb. Easterly winds at 20 kts will not produce a storm surge into SE LA.

[GCANE]

Recon on the way

[supercane4867]

This may not ever make landfall.

[HouTXmetro]

This may not ever make landfall.

A few models hinted at this yesterday

[USTropics]

Can clearly see the LLC on visible now:

[wxman57]

Looks like a 25-30 kt depression. Where the plane found 40-45 kt winds, FL winds were only about 35-40 kts. Buoys in the area reporting mostly 25 kt winds. NHC will call it a 45kt TS at 10am EDT. I'd call it a depression bordering on remnant low. Can't see how a 20-25 kt east wind will produce a surge into MS.

[USTropics]

06z ECMWF shows this becoming decoupled soon, and the LLC never actually makes landfall. It scoots west towards Texas in front of Laura.

[GCANE]

UL Winds may relax a bit by the time it hits the MS Delta

[TheStormExpert]

As I said a few days ago Marco will likely be barely a storm at landfall, maybe even a remnant low. Conditions just aren’t favorable at the moment in the Gulf. Laura should be a different story though.

[USTropics]

Pressure rising, 1007mb on last pass:

[Shell Mound]

Looks like a 25-30 kt depression. Where the plane found 40-45 kt winds, FL winds were only about 35-40 kts. Buoys in the area reporting mostly 25 kt winds. NHC will call it a 45kt TS at 10am EDT. I'd call it a depression bordering on remnant low. Can't see how a 20-25 kt east wind will produce a surge into MS.

Agreed. This lost TS status twelve or more hours ago; scientifically speaking, it should have been downgraded then. But NHC prefers continuity and public safety.

I’m not criticising the NHC’s rationale, but the recently analysed intensities for Marco are among the most generous I’ve ever seen, even in situations involving land.