ATL: MARCO - Remnants - Discussion

[GCANE]

A couple small popups in the swirl, just north of the CoC.
Indicates entrainment of more unstable air.
Watching if the lowering UL winds take them out or not.

[xironman]

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.

Twelve or more hours ago?

Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 24th day of the month at 12:02Z
Agency: United States Air Force
Aircraft: Lockheed WC-130J Hercules with reg. number AF97-5303
Storm Number & Year: 14 in 2020
Storm Name: Marco (flight in the North Atlantic basin)
Mission Number: 11
Observation Number: 02

A. Time of Center Fix: 24th day of the month at 11:31:50Z
B. Center Fix Coordinates: 28.12N 88.35W
B. Center Fix Location: 164 statute miles (264 km) to the SSE (164°) from Gulfport, MS, USA.
C. Minimum Height at Standard Level: 746m (2,448ft) at 925mb
D. Minimum Sea Level Pressure: 1006mb (29.71 inHg) - Extrapolated
E. Dropsonde Surface Wind at Center (Undecoded): NA
F. Eye Character: Not Available
G. Eye Shape: Not Available
H. Estimated (by SFMR or visually) Maximum Surface Wind Inbound: 43kts (49.5mph)

[TallyTracker]

We’ve gotten a major soaking here in the Florida Panhandle. It rained heavy all night. The retention ponds are full and Leon County has opened sandbag filling stations. We’re supposed to get some more rain later today. I’m expecting some localized flooding.

[KimmieLa]

This may not ever make landfall.

A few models hinted at this yesterday

Models hinted at this days ago. And, I am glad it happened.

[TheStormExpert]

Bones where you at!?

 https://twitter.com/stevewafb/status/1297883739054395392

[FLpanhandle91]

I know this storm is an after thought now, but there is a seriously nasty band with strong rotation signatures setting up to come onshore in my area within the next hour or two.

[GCANE]

Convection continues to deepen in the swirl.
Outflow from the strong MCS to the NE may counteract some of the SW UL winds over the CoC.

[GCANE]

Theta-E increasing in the swirl

[wx98]

Still a TS operationally:

10:00 AM CDT Mon Aug 24
Location: 28.5°N 88.5°W
Moving: NNW at 8 mph
Min pressure: 1006 mb
Max sustained: 50 mph

[BobHarlem]

Odd that the Florida panhandle looks to get the worst weather from Marco by far, and they aren't under a watch/warning.

[txwatcher91]

Highest sustained winds offshore are 32mph gusting to 41mph... There is no data out there that supports this being a 50mph TS. I get keeping the public aware but you have to follow what the science shows, even the squalls and rain bands well to the NE of the center only have winds of 40-45mph at 5k feet from the radar. This is IMO at 30mph TD at best. Thankfully impacts will be minimal with Marco.

[TheStormExpert]

And this is still a 45kt TS somehow?

[xironman]

Strong southwesterly shear is taking its toll on Marco, with the
edge of the nearest deep convection now displaced 50 n mi northeast
of the exposed circulation center. Data from an Air Force Reserve
Hurricane Hunter aircraft that investigated the system this morning
measured 45-kt surface winds with the onboard SFMR instrument in
that convection, but winds of only 20 to 30 kt were measured
between this thunderstorm activity and the cyclone's center.
Sampling by the aircraft has also revealed that winds of tropical
storm force are likely no longer occurring in any portion of the
circulation except in that convection. Based on the SFMR data, the
initial intensity is initialized at 45 kt.

[Steve]

Odd that the Florida panhandle looks to get the worst weather from Marco by far, and they aren't under a watch/warning.

Yeah, the shear ghosted all the convection and action offset to the NE.
https://radar.weather.gov/ridge/Conus/s ... y_loop.php

Meanwhile the naked swirl is roughly due south of the AL/MS border.
https://www.star.nesdis.noaa.gov/GOES/f ... d=AL142020

Once the low starts moving west, depending on at what parallel, I'm hoping we'll get some decent gusts and maybe some 25ish sustained tonight to watch. I do expect the nearly-naked swirl to still fire off some storms. Those mostly will be on the MS Coast or south of there again due to the SW shear that should still be present to Marco's south and west.
https://www.star.nesdis.noaa.gov/GOES/f ... d=AL142020

[weathaguyry]

This isn’t surprising, considering how often we see mid level shear wipe out a small storm in hours. Levi Cowan made this scenario very clear in his video last night, pointing out how we’d potentially wake up to a naked swirl SW of the convection racing off with the shear.

[EquusStorm]

90% of Marco is coming ashore in the Florida panhandle now, probably going to have some street flooding, gusty winds and a few tornadoes given the strong rotation moving onshore. I would wager the swirl that makes up the former center won't be quite as consequential except for some coastal flooding.

[wxman57]

I thought that the max sustained wind in a TS/H were supposed to be associated with its circulation. If the winds associated with Marco's circulation are below TS strength, as stated by the NHC, then how is it classified as a TS? Wind gusts in squalls don't count. I know the NHC doesn't want those in SE LA and Mississippi to ignore Marco, but it's really not a threat any longer. It's a remnant low with 25-30 mph wind. Doesn't even qualify as a TD with the lack of persistent convection around the center. OK, enough on Marco, need to watch Laura, the real threat.

[xironman]

I thought that the max sustained wind in a TS/H were supposed to be associated with its circulation. If the winds associated with Marco's circulation are below TS strength, as stated by the NHC, then how is it classified as a TS? Wind gusts in squalls don't count. I know the NHC doesn't want those in SE LA and Mississippi to ignore Marco, but it's really not a threat any longer. It's a remnant low with 25-30 mph wind. Doesn't even qualify as a TD with the lack of persistent convection around the center. OK, enough on Marco, need to watch Laura, the real threat.

Of course you are correct but I did not know squalls did not count.

H. Estimated (by SFMR or visually) Maximum Surface Wind Inbound: 46kts (52.9mph)
I. Location & Time of the Estimated Maximum Surface Wind Inbound: 69 nautical miles (79 statute miles) to the NE (51°) of center fix at 16:22:30Z
J. Maximum Flight Level Wind Inbound: From 99° at 38kts (From the E at 43.7mph)
K. Location & Time of the Maximum Flight Level Wind Inbound: 81 nautical miles (93

BTW: It looks like the surface low has stalled.

[wx98]

Special Advisory. Watches/warnings cancelled. Down to 40 mph:

Tropical Storm Marco Special Advisory Number 18
NWS National Hurricane Center Miami FL AL142020
100 PM CDT Mon Aug 24 2020

...MARCO WEAKENS...
...GUSTY WINDS AND HEAVY RAINFALL STILL POSSIBLE OVER PORTIONS OF
THE NORTHERN GULF COAST THROUGH TONIGHT...


SUMMARY OF 100 PM CDT...1800 UTC...INFORMATION
----------------------------------------------
LOCATION...28.7N 88.6W
ABOUT 40 MI...65 KM SE OF THE MOUTH OF THE MISSISSIPPI RIVER
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...NW OR 320 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES

[MarioProtVI]

As wxman would say, it’s dead Jim!!


(I had to sorry , this’ll be dead by 11pm most likely then the real Bones can make an appearance)