ATL: HARVEY - Post-Tropical - Discussion

[Frank P]

just absolutely amazing, been a while since we've seen such a storm out in the GOM... still wondering just how intense it can get, I guess a Cat 4 or even the dreaded 5 is not out of the question... not much difference in an upper end 4 or low end 5 though.. going to be fascinating to watch unfold real time... my heart goes out to all in harms way of this monster... as many others, reliving flashbacks of Katrina as it was heading towards the MS/LA line... and how desperately I was hoping it would just go more west or weaken, so glad it is not us this time, but yet feel guilty thinking like this... Harvey is going to affect coastal areas for many years... lives will be lost, lives will be drastically changed, bridges will be destroyed along with coastal infrastructure, damage will be tremendous, and it's going to leave a deep scare for many to bear... with Katrina the faith biased groups came down in multitudes and really helped the Coast in the initial weeks and months... And I expect that to be the case for Texas.. This is not speculation, this is a fact! America will come to your aid Texas, but sadly it's going to take a long time for recovery..

[tolakram]

The latest drop appears to show just 11kts of shear over the center. Remember even 15kts is not destructive and you can certainly have a major hurricane if all other conditions are good.

[GCANE]

Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 25th day of the month at 11:33Z
Agency: United States Air Force
Aircraft: Lockheed WC-130J Hercules with reg. number AF97-5305
Storm Number & Year: 09 in 2017
Storm Name: Harvey (flight in the North Atlantic basin)
Mission Number: 17
Observation Number: 17
A. Time of Center Fix: 25th day of the month at 11:22:30Z
B. Center Fix Coordinates: 26°18'N 95°48'W (26.3N 95.8W)
B. Center Fix Location: 108 statute miles (173 km) to the ENE (76°) from Brownsville, TX, USA.
C. Minimum Height at Standard Level: 2,657m (8,717ft) at 700mb
D. Estimated (by SFMR or visually) Maximum Surface Wind Inbound: 74kts (~ 85.2mph)
E. Location of the Estimated Maximum Surface Wind Inbound: 7 nautical miles (8 statute miles) to the SSW (194°) of center fix
F. Maximum Flight Level Wind Inbound: From 284° at 80kts (From the WNW at ~ 92.1mph)
G. Location of Maximum Flight Level Wind Inbound: 8 nautical miles (9 statute miles) to the SSW (198°) of center fix
H. Minimum Sea Level Pressure: 951mb (28.09 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 14°C (57°F) at a pressure alt. of 3,046m (9,993ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 3,052m (10,013ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 12°C (54°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Open in the southeast, SE
M. Eye Shape & Diameter: Circular with a diameter of 12 nautical miles (14 statute miles)
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Levels (sfc and flt lvl centers are within 5nm of each other): Surface and 700mb
O. Navigational Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 1.25 nautical miles

Remarks Section:
Maximum Outbound and Flight Level Wind: 96kts (~ 110.5mph) which was observed 10 nautical miles (12 statute miles) to the NE (42°) from the flight level center at 11:25:30Z
Dropsonde Surface Wind at Center: From 230° at 8kts (From the SW at 9mph)

[tolakram]

If you look at previous drops the winds at the upper levels were higher. Now if this is an indication of shear or something else ... a pro met will have to chime in.

https://www.tropicaltidbits.com/recon/#AF3051709AHARVEY

[NDG]

Perhaps is just that the eye is expanding.

[forecasterjack]

Not quite perfect environment, but pretty darn close. Shear not the biggest issue, dry air is IMO. Can see it wrapping in on IR, separating spiral bands from CDO. If no dry air, this would be a cat 4 by now. If there was any more shear than 5-10kts, it would be a cat 1/2 IMO https://weather.us/satellite/921-w-267- ... .html#play

[tolakram]

60 frame 1 sec IR loop

http://rammb-slider.cira.colostate.edu/?sat=goes-16&sec=mesoscale_01&x=998&y=908.5&z=2&im=60&ts=1&st=0&et=0&speed=130&motion=loop&map=1&lat=0&p%5B0%5D=10&opacity%5B0%5D=1&hidden%5B0%5D=0&pause=0&slider=-1&hide_controls=0&mouse_draw=0&s=rammb-slider

[tolakram]

Not quite perfect environment, but pretty darn close. Shear not the biggest issue, dry air is IMO. Can see it wrapping in on IR, separating spiral bands from CDO. If no dry air, this would be a cat 4 by now. If there was any more shear than 5-10kts, it would be a cat 1/2 IMO https://weather.us/satellite/921-w-267- ... .html#play

Maybe My understanding is that while some dry air exists it's the shear that makes dry air an issue, otherwise it's easily walled off, to a degree anyway. Regardless you make a good point, I'm really not sure which is more important in this case.

[JtSmarts]

Hurricane Force winds now extend out 35 miles from the center. An increase from 25 miles.

[SouthDadeFish]

There are definitely concentric rings on radar, but recon isn't finding any obvious secondary wind maxima. If there is an EWRC occurring, it is not your typical one.... Yet. Regardless, Harvey continues to intensify at impressive rates. Given the small core, I am surprised the winds aren't stronger. Convection is relatively robust for the Atlantic basin, likely due to the very warm waters in the Gulf right now.

[forecasterjack]

Not quite perfect environment, but pretty darn close. Shear not the biggest issue, dry air is IMO. Can see it wrapping in on IR, separating spiral bands from CDO. If no dry air, this would be a cat 4 by now. If there was any more shear than 5-10kts, it would be a cat 1/2 IMO https://weather.us/satellite/921-w-267- ... .html#play

Maybe My understanding is that while some dry air exists it's the shear that makes dry air an issue, otherwise it's easily walled off, to a degree anyway. Regardless you make a good point, I'm really not sure which is more important in this case.

Dry air is an issue because it gets entrained into thunderstorm updrafts. When this happens, it evaporationally cools and results in convectively stable parcels. These then sink and extinguish the thunderstorm updrafts, weakening the storm. Dry air has been in and around the storm all along. It's trying to mix out the dry air and is making some headway. Shear is bad because it tilts the updrafts so that they can't organize and rotate around a common center. Shear can also drive dry air into the center of the storm. The dry air now is in the outer parts of the system which is why it's still intensifying. If there was more shear to force that dry air in, we'd be looking at a low end hurricane attm.

[Hypercane_Kyle]

Dropsonde just pegged 120mph just 1,270 ft from the surface.

[NDG]

If you look at previous drops the winds at the upper levels were higher. Now if this is an indication of shear or something else ... a pro met will have to chime in.

https://www.tropicaltidbits.com/recon/#AF3051709AHARVEY

The dropsondes from the recon hunters only show from H70, their highest cruising altitudes during their flights in a hurricane. A strong hurricane circulation is stacked really high, so its strong winds are found at high altitudes as well, but not as strong as at h85.

[Hypercane_Kyle]

Also from dropsonde.

958mb
70° (from the ENE)
103 knots (119 mph)

We may have a major hurricane now.

[BRweather]

wow

[SouthDadeFish]

Besides the storm surge threat along the coast, this graphic is what scares me the most:



It is hard to comprehend what 20+ inches of rain is like. Not only this, but to have 20+ inches of rain over such a large area is truly incredible. I am very afraid of the potential for significant inland flooding. Remember, water is what tends to kill people in tropical cyclones. Many people think it is okay to drive through roads in which they cannot see the bottom of the water. Do not do this. Turn around - don't drown!

[drezee]

Also from dropsonde.

958mb
70° (from the ENE)
103 knots (119 mph)

We may have a major hurricane now.

I think we do

[tolakram]

If you look at previous drops the winds at the upper levels were higher. Now if this is an indication of shear or something else ... a pro met will have to chime in.

https://www.tropicaltidbits.com/recon/#AF3051709AHARVEY

The dropsondes from the recon hunters only show from H70, their highest cruising altitudes during their flights in a hurricane. A strong hurricane circulation is stacked really high, so its strong winds are found at high altitudes as well, but not as strong as at h85.

So are those winds at the various heights below the plane just eyewall winds? I completely forgot about the plane altitude so of course they aren't sampling the upper levels.

[NDG]

If you look at previous drops the winds at the upper levels were higher. Now if this is an indication of shear or something else ... a pro met will have to chime in.

https://www.tropicaltidbits.com/recon/#AF3051709AHARVEY

The dropsondes from the recon hunters only show from H70, their highest cruising altitudes during their flights in a hurricane. A strong hurricane circulation is stacked really high, so its strong winds are found at high altitudes as well, but not as strong as at h85.

So are those winds at the various heights below the plane just eyewall winds? I completely forgot about the plane altitude so of course they aren't sampling the upper levels.

Yes Sir, depending where they drop them, the last one was dropped on the NE quadrant, because of the circulation it landed on the northern eyewall quadrant as it fell down, that's why you see the shift in the winds.

[forecasterjack]

Convection has rapidly stabilized in Harvey's core. We now have gotten rid of the unstable/wobbly hot tower structures, replaced by a ring of smooth and powerful convection. GOES16 loop shows it best: https://weather.us/satellite/921-w-267- ... .html#play