ATL: GRACE - Remnants - Discussion

[Hypercane_Kyle]

Solid case for 85 knots, MSLP 968 mb IMO. Won't be surprised if the winds begin to catch up soon either.

[supercane4867]

100kt landfall isn't too far of a stretch given current trends

[NDG]

968 mbar, 11 mbar lower than NHC's latest value. First pass (NE to the center) has winds that seem to indicate a cat 2, even though the NW quadrant (not sampled yet) might still have stronger winds based on IR.

Pressure = 968.0 mbar
SFMR = 84 kt
Est. Sfc. Wind = 76.7 kt

It actually came in throught the eastern Quadrant, so I am sure there are stronger winds in the Northern quadrant.

[skyline385]

That was a big dip, although kinda expected since it was losing 1mb per pass during last recon...

[aspen]

The drop from ~980mb extrapolated and 968mb between the two flights indicates a deepening rate of 1.57 mb/hr. This could pick up as Grace’s eye clears out, but if it continues right up until landfall at approximately 3am tomorrow morning, Grace will peak at around 957mb.

[NDG]

Wow, western quadrant is even stronger at flight level.

URNT15 KNHC 202357
AF309 1907A GRACE HDOB 19 20210820
234730 2034N 09550W 6960 02935 9750 +125 //// 316064 068 077 006 01
234800 2033N 09552W 6962 02943 //// +111 //// 314075 084 077 007 01
234830 2032N 09553W 6969 02945 //// +091 //// 310089 093 073 011 01
234900 2031N 09554W 6962 02968 //// +080 //// 317094 097 073 010 01
234930 2029N 09555W 6954 02993 //// +077 //// 321095 097 075 011 01
235000 2028N 09557W 6967 02999 //// +074 //// 321090 093 069 011 01
235030 2027N 09558W 6956 03027 //// +075 //// 319080 088 066 014 01
235100 2026N 09559W 6971 03020 //// +080 //// 317072 077 063 006 01
235130 2024N 09600W 6957 03048 9896 +108 //// 317067 070 061 004 01
235200 2023N 09602W 6968 03045 9919 +092 //// 318064 067 060 004 01
235230 2022N 09603W 6957 03067 //// +087 //// 318064 066 058 005 01
235300 2021N 09604W 6965 03062 //// +072 //// 312059 063 056 012 01
235330 2020N 09606W 6964 03067 //// +069 //// 304055 057 053 015 01
235400 2018N 09607W 6959 03081 //// +067 //// 301054 055 051 010 01
235430 2017N 09608W 6965 03079 //// +070 //// 303052 053 051 006 01
235500 2016N 09609W 6960 03085 //// +073 //// 308052 052 051 005 01
235530 2015N 09611W 6963 03084 9983 +079 //// 310052 053 049 003 01
235600 2014N 09612W 6962 03087 9973 +087 //// 311051 052 046 004 01
235630 2012N 09613W 6963 03089 9974 +090 //// 314052 052 046 003 01
235700 2011N 09614W 6962 03092 9976 +090 //// 318051 052 045 003 01
$$

[ThetaE]

Yeah it needs to wrap that convection first.

Its had curling CBs across the entire cdo for the past two hours. Take a look at the satellite imagery.

I know but the eye needs to pop before serious pressure falls occur

First, it doesn't really need to pop an eye before pressure falls can occur. Often when you have a quickly intensifying storm with rotating CBs, cirrus clouds will obscure the eye for a long period of time, even as subsidence in the center ramps up. IMO the appearance of an eye is really favored at the end of an intensification phase for that reason, though IDK if that's been studied/well-documented.

Second, there's definitely been some suspicious warming on IR satellite in the last ~30 min.

[ThetaE]

Dropsonde got 968mb at 11kt, so good for 967mb.

[galaxy401]

Dropsonde got 968mb at 11kt, so good for 967mb.

Yep that's what the NHC is using. Category 2 now!

[AlphaToOmega]

Now at 85 knots

7:00 PM CDT Fri Aug 20
Location: 20.7°N 95.7°W
Moving: W at 10 mph
Min pressure: 967 mb
Max sustained: 100 mph

[NDG]

Closed eyewall.

38
URNT12 KNHC 202359
VORTEX DATA MESSAGE AL072021
A. 20/23:44:40Z
B. 20.69 deg N 095.70 deg W
C. 700 mb 2845 m
D. 968 mb
E. 315 deg 11 kt
F. CLOSED
G. C32
H. 84 kt
I. 076 deg 26 nm 23:37:00Z
J. 174 deg 83 kt
K. 076 deg 29 nm 23:36:00Z
L. 77 kt
M. 229 deg 10 nm 23:47:30Z
N. 320 deg 97 kt
O. 228 deg 17 nm 23:49:30Z
P. 8 C / 3049 m
Q. 16 C / 3050 m
R. 10 C / NA
S. 12345 / 7
T. 0.02 / 2 nm
U. AF309 1907A GRACE OB 04
MAX FL WIND 97 KT 228 / 17 NM 23:49:30Z
;

[NDG]

32 nautical miles eye that's pretty big one.

[ThetaE]

Well I'm happy with calling 965-970mb, but I should've known better about the winds. Explanations for why they're lower given the pressure drop:

1. Grace has had, and continues to have, a large eye (32 nm per VDM). This is probably the main explanation.

2. Winds tend to lag behind pressure falls in periods of RI. My understanding, though, is that has to do with winds mixing down to the surface. I have to say I wasn't too blown away by the flight-level winds to really think that's what's going on here.

[Nimbus]

Big eye means more inflow maybe catch a little dry air before landfall?
Sadly the inflow is being moistened by gulf moisture from the east and the models showed RI.

[LAwxrgal]

Thankfully this doesn't have more time over the GOM bathwater.

[skyline385]

Looks like its opening up

[Astromanía]

Eye is appearing now

[Hypercane_Kyle]

Very rapid improvement in IR structure now. Grace has enough time over water to reach Cat 3.

[Astromanía]

Very rapid improvement in IR structure now. Grace has enough time over water to reach Cat 3.

Could be the first major landfall in Mexico since Willa 2018 and the first major hurricane impacting Mexico from the atlantic since Karl 2010 almost in the same location

[Hypercane_Kyle]

Cat 2 winds on the SE quad. I wouldn't be surprised if the NE quad is closer to 90 knots now.