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Hurricane Isaac, Part 3 - Analysis and Forecasting Thread


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Product: Air Force Vortex Message (URNT12 KNHC)

Transmitted: 28th day of the month at 17:33Z

Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 306)

Storm Number & Year: 09L in 2012

Storm Name: Isaac (flight in the North Atlantic basin)

Mission Number: 31

Observation Number: 19

A. Time of Center Fix: 28th day of the month at 16:48:50Z

B. Center Fix Coordinates: 28°22'N 88°36'W (28.3667N 88.6W)

B. Center Fix Location: 142 miles (228 km) to the SE (142°) from New Orleans, LA, USA.

C. Minimum Height at Standard Level: 1,222m (4,009ft) at 850mb

D. Estimated (by SFMR or visually) Maximum Surface Wind: 66kts (~ 76.0mph)

E. Location of the Estimated Maximum Surface Wind: 44 nautical miles (51 statute miles) to the NE (55°) of center fix

F. Maximum Flight Level Wind Inbound: From 145° at 89kts (From the SE at ~ 102.4mph)

G. Location of Maximum Flight Level Wind Inbound: 53 nautical miles (61 statute miles) to the NE (54°) of center fix

H. Minimum Sea Level Pressure: 975mb (28.79 inHg)

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17°C (63°F) at a pressure alt. of 1,443m (4,734ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 23°C (73°F) at a pressure alt. of 1,524m (5,000ft)

K. Dewpoint Temp (collected at same location as temp inside eye): 20°C (68°F)

K. Sea Surface Temp (collected at same location as temp inside eye): Not Available

L. Eye Character (Undecoded): SPIRAL BAND

M. Eye Shape: Elliptical (oval shaped)

M. Orientation of Major Axis in Elliptical Eye: 110° to 290° (ESE to WNW)

M. Length of Major Axis in Elliptical Eye: 70 nautical miles (81 statute miles)

M. Length of Minor Axis in Elliptical Eye: 60 nautical miles (69 statute miles)

N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature

N. Fix Level: 850mb

O. Navigation Fix Accuracy: 0.02 nautical miles

O. Meteorological Accuracy: 1 nautical mile

Remarks Section:

Maximum Flight Level Wind: 94kts (~ 108.2mph) in the east quadrant at 15:50:30Z

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L. Eye Character (Undecoded): SPIRAL BAND

Very key as to why we have not seen any RI. Single, coiled, spiral bands take longer to transfer winds into the core as opposed to having a ring of convection with many "feeder" type bands "spiraling into" the ring core. From a geometric perspective, single spirals don't transfer vorticity nor thermodynamic feedbacks into the center very well. The 6C difference is nice, but it was 4C last night....so more evidence of just slow, methodical strengthening.

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I've been watching the trends of the possible future motion of Isaac and the HRRR is very interesting because it too has the slow west drift just south of the LA coast, but it actually turns it WSW and maybe even SW. Could this type of motion actually happen later today and tonight?

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Sounds like our local weather here in SE Texas is grabbing on to the westward drift of Issac. This morning they were saying mostly sunny and breezy tomorrow. The weather at noon was calling for cloudy and windy tomorrow with rain east of HOU, with a good chance of rain and wind tomorrow night over the entire Houston area. Considering the wind field we may see 30-35 MPH winds here tomorrow, especially if some of the western model trends hold.

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New 12Z ECMWF has shifted back a little east of its previous run. All models have it near over water for at least another 24-36 hours. Certainly doesn't look like it's going anywhere fast any time soon.

Eyewall has just about completely closed off on KLIX radar now.

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The lowest pressure on the 12z Euro is actually sub 960mb at the 33h mark.

Did the Euro initalize with the current presurre of Issac?

yeah not sure why no one is commenting, to debunk or otherwise...

sub-960 mb is considerably more intense than the 0Z Euro, and depicts an even longer scraping along the southeast LA coast

for 18Z 8/28 Euro had 972 mb vs. 975 mb extrap on 17:42Z VDM

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Would the sub-960 progged by the Euro imply a Cat 2 or higher?

Keep in mind that we've already broken a record for having the lowest pre-hurricane tropical storm pressure in history, so trying to correlate the pressure verses the wind field has proven futile. Considering the pressure is at 975 millibars with 75 MPH winds, it seems reasonable that we won't be seeing sustained winds over 90 MPH and even that is pushing it. However, if the "rubber band effect" of the low pressure and low wind field breaks and we get an inner core that can develop, winds may react a bit more. Isaac is almost out of time.

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