ATL: NATE - Post Tropical - Discussion

[stormreader]

00Z CMC

Continues with a west component right into landfall. Further west than Euro. Takes it west inland west of New Orleans.

[NDG]

Now is when radar is starting to catch the norther eyewall of Nate, not the eye, but remember that this is way on the top of the clouds.

[Airboy]

Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 7th day of the month at 14:47Z
Agency: United States Air Force
Aircraft: Lockheed WC-130J Hercules with reg. number AF97-5305
Storm Number & Year: 16 in 2017
Storm Name: Nate (flight in the North Atlantic basin)
Mission Number: 8
Observation Number: 13
A. Time of Center Fix: 7th day of the month at 14:17:50Z
B. Center Fix Coordinates: 26°28'N 88°19'W (26.4667N 88.3167W)
B. Center Fix Location: 265 statute miles (426 km) to the SSE (156°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 2,955m (9,695ft) at 700mb
D. Estimated (by SFMR or visually) Maximum Surface Wind Inbound: 82kts (~ 94.4mph)
E. Location of the Estimated Maximum Surface Wind Inbound: 21 nautical miles (24 statute miles) to the ENE (66°) of center fix
F. Maximum Flight Level Wind Inbound: From 143° at 81kts (From the SE at ~ 93.2mph)
G. Location of Maximum Flight Level Wind Inbound: 35 nautical miles (40 statute miles) to the ENE (64°) of center fix
H. Minimum Sea Level Pressure: 985mb (29.09 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 10°C (50°F) at a pressure alt. of 3,045m (9,990ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 2,973m (9,754ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 6°C (43°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Open in the southwest, SW
M. Eye Shape & Diameter: Circular with a diameter of 24 nautical miles (28 statute miles)
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Level: 700mb
O. Navigational Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 1 nautical mile

Remarks Section:
Maximum Flight Level Wind: 84kts (~ 96.7mph) which was observed 52 nautical miles (60 statute miles) to the ESE/SE (124°) from the flight level center at 12:55:50Z
Dropsonde Surface Wind at Center: From 95° at 9kts (From the E at 10mph)

[drezee]

Drop says 985, but heights 15m lower. Pressure will in next pass to at least 982mb. Closer 980...not good

[GCANE]

[GCANE]

[tarheelprogrammer]

I believe that was a bad pass, but they are the experts. Why was the pressure around 980 mb, but they went with 985? I am just a clueless guy when it comes to this stuff, and I am wondering why.

[stormreader]

[quote="PandaCitrus"]The formula im aware of is 2x forward speed =44mph in difference between the strong and weak sides of a hurricane.

If max winds are 100mph at landfall, the west side should only get 55mph winds according to the formula.[/quote
I like the thought behind the formula, but as for specifics, I don't know. No doubt the east side gets an extra kick. However, I don't think there is an equal amount of subtraction on the west. My hunch is that at landfall, with the effects of friction, and the sudden expansion of isobars and and windfield to a larger area, that the subtraction on the west, will not equal the addition on the east.

[Ken711]

WTNT41 KNHC 071455
TCDAT1

Hurricane Nate Discussion Number 13
NWS National Hurricane Center Miami FL AL162017
1000 AM CDT Sat Oct 07 2017

Nate is showing improved organization in satellite imagery this
morning, with the formation of a symmetric central dense overcast
with cloud tops colder than -80C. In addition, Air Force Reserve
and NOAA Hurricane Hunter aircraft have reported a central pressure
near 984 mb inside a 25 n mi wide eye that is starting to form under
the overcast. The planes have reported 700-mb flight level winds of
up to 88 kt and surface wind estimates from the SFMR instrument
between 75-85 kt. Based on these data, the initial intensity is
increased to a possibly conservative 80 kt.

Conditions appear favorable for Nate to continue strengthening for
the next 12 h or so before it encounters land and increasing shear.
The new intensity forecast thus follows the SHIPS model in showing
Nate become a Category 2 hurricane before landfall on the central
Gulf Coast. After landfall, Nate should weaken rapidly as it moves
through the eastern United States. The cyclone is now forecast to
become extratropical near the 72 hr point and dissipate completely
by 96 h.

The initial motion is toward the north-northwest at a very rapid 24
kt. The hurricane is being steered by the flow between a large
cyclonic gyre over the southwestern Gulf of Mexico and a mid-level
ridge over the western Atlantic. In addition, a mid-latitude trough
in the westerlies is moving eastward through the central United
States. This pattern is expected to cause Nate to turn northward
during the next 12-18 h as it rounds the western end of the ridge,
followed by a turn toward the northeast as it enters the westerlies.
The new forecast track is nudged a little to the left of the
previous track, and it lies near the center of the tightly clustered
guidance.

KEY MESSAGES:

1. Nate is expected to bring life-threatening storm surge flooding
near and well east of where the center makes landfall, and a storm
surge warning is in effect from Morgan City, Louisiana, to the
Okaloosa/Walton county line in Florida. Maximum flooding of 7 to 11
feet above ground level is expected in portions of southeastern
Louisiana and along the Mississippi coast. Residents in these areas
should immediately heed any evacuation instructions given by local
officials.

2. Nate is forecast to reach Category 2 intensity before landfall.
A hurricane warning is in effect for portions of the northern Gulf
Coast from Louisiana to Alabama, with the strongest winds expected
to occur primarily to the east of the center. Preparations to
protect life and property should be rushed to completion in these
areas, as tropical storm conditions will first arrive in the warning
area this afternoon.

3. Nate's fast forward speed after landfall will bring tropical-
storm-force winds well inland across portions of the southeastern
U.S. Tropical storm watches and warnings are in effect for portions
of southeastern Mississippi, Alabama, and western Georgia.

4. Nate will bring heavy rainfall of 3 to 6 inches with isolated
totals of 10 inches east of the Mississippi River from the central
Gulf Coast into the Deep South, eastern Tennessee Valley, and
southern Appalachians through Monday, resulting in the potential for
flash flooding in these areas.

5. Moisture from Nate interacting with a frontal zone will also
bring 2 to 4 inches of rain with isolated totals of 6 inches across
the Ohio Valley and central Appalachians Sunday and Monday, which
will increase the risk for flash flooding across these locations.

FORECAST POSITIONS AND MAX WINDS

INIT 07/1500Z 26.6N 88.4W 80 KT 90 MPH
12H 08/0000Z 29.1N 89.0W 90 KT 105 MPH
24H 08/1200Z 32.1N 88.3W 60 KT 70 MPH...INLAND
36H 09/0000Z 35.7N 85.5W 35 KT 40 MPH...INLAND
48H 09/1200Z 39.2N 80.6W 30 KT 35 MPH...INLAND
72H 10/1200Z 44.5N 67.5W 25 KT 30 MPH...POST-TROP/EXTRATROP
96H 11/1200Z...DISSIPATED

[PandaCitrus]

NHC discussion is out. They are now forecasting Cat 2 105mph winds at landfall and say current intensity of 90mph may be conservative.

[Javlin]

B. 26 deg 28 min N
088 deg 19 min W

26.5N and 88.3W NHC position 12H 07/1800Z 27.3N 88.3W 75 KT 85 MPH
alittle W but may go N more?

[Airboy]

I believe that was a bad pass, but they are the experts. Why was the pressure around 980 mb, but they went with 985? I am just a clueless guy when it comes to this stuff, and I am wondering why.

Because the drop sonde said it was 985. What I see the Extrap. Sfc. Press from the planes are always a bit lower than the readings from drop sondes. If you add 1-2 mb to the extrap you mostly get the pressure NHC will use.

[GCANE]

 https://twitter.com/NASA_SPoRT/status/916654185311031296

[stormreader]

Officials now calling for Cat 2--think most of us saw that coming. Looking at landfall along the Miss Coast. Watching to see if storm has begun that mostly due N trek. I can't tell yet.

[Raebie]

Now a Cat 2.

[Ken711]

Now a Cat 2.

Not yet, but NHC is forecasting an increase to Cat 2 at landfall.

[GCANE]

 https://twitter.com/NWSNewOrleans/status/916679116052746240

[stormreader]

Officials now calling for Cat 2--think most of us saw that coming. Looking at landfall along the Miss Coast. Watching to see if storm has begun that mostly due N trek. I can't tell yet.

I'm actually still not convinced with the landfall in Miss. It will pretty much have to make that N movement from here on out to do that. Any further west component at all, will likely bring it in west of the Miss River and toward that Grand Isle area. IMO

[GCANE]

 https://twitter.com/Jeff_Piotrowski/status/916681048016277505

[GCANE]

 https://twitter.com/NHC_Atlantic/status/916681165322506240