Tropical Depression Isaac:

[redneckweather]

Gene, I'm thinking the westward trend we saw today has ended and models will swing back east a bit, just like the latest GFS run did. I would expect the overnight Euro run to do the same as well. I guess I will find out in the morning since I won't be staying up to see it. lol

[Scott747]

With all the 0z model runs in with the G-IV data a remarkable consensus has centered between Mobile and Panama City with the Euro having a major shift and now agreeing with the consensus.

Now the northern vort and current location of the official center needs to become dominant for the models to have validity.

As always things could change....

[ejburas]

VORTEX DATA MESSAGE AL092012
A. 24/06:55:40Z
B. 15 deg 03 min N
069 deg 35 min W
C. 850 mb 1420 m
D. 37 kt
E. 211 deg 6 nm
F. 116 deg 38 kt
G. 011 deg 168 nm
H. 1000 mb
I. 17 C / 1524 m
J. 18 C / 1513 m
K. 17 C / NA
L. NA
M. NA
N. 1345 / 8
O. 0.02 / 10 nm
P. AF300 1009A ISAAC OB 03
MAX FL WIND 38 KT N QUAD 05:27:30Z
MAX FL TEMP 20 C 332 / 71 NM FROM FL CNTR

There's the new center, roughly 120 miles SW/SSW from the 1am advisory...

[srainhoutx]

I'd like to see the second pass to confirm that this is in fact the 'true center'.

[srainhoutx]

Morning e-mail from Jeff:

Isaac becoming slightly better organized over the central Caribbean Sea

Discussion:
An onslaught of aircraft have been sampling the atmosphere in and around Isaac over the past 24 hours including a high attitude GIV mission over the Bahamas and several recon missions. Latest mission is in progress at this time and continues to suggest a disorganized tropical system with low level and mid level centers not aligned. There is a low level center around 16.7N that has been tracked for the advisory position for the past 36 hours, but a well defined mid level position (700-850mb) well to the S/SSW of the northern low level center. The most recent passes suggest that a new low level center may be forming under the mid level center which could result in a significant near term shift to the SW of the center location. One thing is for sure, convection has been vigorous overnight near the mid level center.

Track:
After some really big westward track shifts by nearly all the models yesterday afternoon most have swung back eastward overnight on their 00Z runs including the ECMWF. In fact the 00Z ECMWF and GFS and almost identical in their track out through 5 days. This is the first time that there has been an overall consensus with the track and some of the GIV data did get into these runs. Would like to at least see 1-2 more runs (12Z today and 00Z tonight) to see if this trend holds and what if any impact the relocation of the center may have.

Based on the potential for the center relocation and looking at IR images this morning, it would appear Isaac is going to miss Hispaniola to the south unless it takes a hard right turn and starting gaining latitude. I think there has been some uncertain motion over the past 24 hours based on tracking and merging of multiple centers and NHC trying to hold some continuity between advisory packages. We need to get a well defined low level center with good fixes to have some confidence in the motion.

Based on all of this and including the potential for a center relocation, the guidance is still in very good agreement out through 72 hours on Isaac rounding the western side of the ridge over the Atlantic and turning NW toward the weakness over the SE US. This tracks the system over east or center Cuba and then across the FL Straits and Keys and then into the eastern Gulf of Mexico. The guidance spread enlarges some beyond 72 hours after Isaac reaches the eastern Gulf, but there is still decent agreement amongst the major models showing a track toward the central/east US Gulf coast from MS to the FL panhandle. I still do not see a major trough capture pattern in most of the model solutions with several showing a continued NW/NNW motion after landfall and a significant slowing of forward speed suggesting high pressure is going to be building in north and over the top of the system. This has continued to be the controlling factor on track in the long range period and has to do with the movement and intensity of short waves moving onshore over the PAC NW and the downstream ridge intensity and position over the southern plains. Models tend to under-estimate the ridging at times which is why I would like to see the current consensus hold for the next two guidance cycles.


Based on everything and the current guidance/NHC track a hurricane should be nearing the US Gulf coast late Tuesday into early Wednesday morning. It is a good time to remind everyone that the error in track at 4-5 days in around 200 miles and this system will be large in size and have far reaching impacts.

Intensity:
Isaac has failed to intensify much to this point mainly due to the lack of organization of its inner core. There continues to be dry air entangled with the system which has limited the convection for most of its life to the SW semi-circle. Additionally large circulations, such as Isaac has, usually take time to consolidate. Until Isaac can consolidate its inner core any intensification will be slow. The interaction of land continues to also offer some challenges to the intensity forecast, but the mountains of Hispaniola may not play as big of a role as before. Once into the Gulf of Mexico the system should be in an environment favorable for intensification and most of the models support that although none are overly aggressive. We will have to see how long it takes the inner core to re-form if it is highly disrupted with its passage over any of the islands in the next 72 hours. Based on the available intensity guidance, Isaac should reach hurricane intensity in the SE Gulf of Mexico and approach the US Gulf coast as a 800-95mph hurricane.

NHC Track and Error Cone:

[srainhoutx]

First visible imagery as well as microwave and RECON data suggests Isaac is beginning a strengthening phase. The 700mb/850mb as well as surface circulation are becoming a bit better organized and appear to be transitioning to a more vertically stack cyclone.

[srainhoutx]

Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 24th day of the month at 12:24Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 10
Observation Number: 17
A. Time of Center Fix: 24th day of the month at 12:14:00Z
B. Center Fix Coordinates: 15°40'N 70°26'W (15.6667N 70.4333W)
B. Center Fix Location: 198 miles (318 km) to the S (190°) from Santo Domingo, Dominican Republic.
C. Minimum Height at Standard Level: 1,430m (4,692ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 31kts (~ 35.7mph)
E. Location of the Estimated Maximum Surface Wind: 69 nautical miles (79 statute miles) to the WSW (258°) of center fix
F. Maximum Flight Level Wind Inbound: From 340° at 26kts (From the NNW at ~ 29.9mph)
G. Location of Maximum Flight Level Wind Inbound: 71 nautical miles (82 statute miles) to the W (261°) of center fix
H. Minimum Sea Level Pressure: 1000mb (29.53 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17°C (63°F) at a pressure alt. of 1,525m (5,003ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 1,518m (4,980ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 17°C (63°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 10 nautical miles
Remarks Section:
Maximum Flight Level Wind: 58kts (~ 66.7mph) in the northeast quadrant at 10:22:00Z
Maximum Flight Level Temp: 18°C (64°F) which was observed 66 nautical miles (76 statute miles) to the WSW (258°) from the flight level center

[MontgomeryCoWx]

It looks more south there than a 16.7 center.

[MontgomeryCoWx]

And there we have it... a 15.4 N center.

[srainhoutx]

06Z HWRF:

[srainhoutx]

Notice the the internal position is a slight shift further S. This is typical and until we get a very well defined circulation 'center', expect further adjustments.

AL, 09, 2012082412, , BEST, 0, 159N, 704W, 45, 1000, TS,

[srainhoutx]

Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 24th day of the month at 12:58Z
Corrected: This observation corrected a previous observation.
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 10
Observation Number: 17
A. Time of Center Fix: 24th day of the month at 12:14:00Z
B. Center Fix Coordinates: 15°40'N 70°26'W (15.6667N 70.4333W)
B. Center Fix Location: 198 miles (318 km) to the S (190°) from Santo Domingo, Dominican Republic.
C. Minimum Height at Standard Level: 1,430m (4,692ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 31kts (~ 35.7mph)
E. Location of the Estimated Maximum Surface Wind: 69 nautical miles (79 statute miles) to the WSW (258°) of center fix
F. Maximum Flight Level Wind Inbound: From 340° at 26kts (From the NNW at ~ 29.9mph)
G. Location of Maximum Flight Level Wind Inbound: 71 nautical miles (82 statute miles) to the W (261°) of center fix
H. Minimum Sea Level Pressure: 1000mb (29.53 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17°C (63°F) at a pressure alt. of 1,525m (5,003ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 1,518m (4,980ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 17°C (63°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 10 nautical miles
Remarks Section:
Maximum Flight Level Wind: 58kts (~ 66.7mph) in the northeast quadrant at 10:22:00Z
Maximum Flight Level Wind Outbound: 66kts (~ 76.0mph) in the east quadrant at 12:43:40Z
Maximum Flight Level Temp: 18°C (64°F) which was observed 66 nautical miles (76 statute miles) to the WSW (258°) from the flight level center

[unome]

from the Chris Hollis, who owns tropicalatlantic.com & wrote the live-recon-mapping program there

http://www.canetalk.com/2012/08/1345818274.shtml

[srainhoutx]

Further adjustment on internal numbers:

AL, 09, 2012082412, , BEST, 0, 159N, 704W, 50, 1000, TS, 50,

[wxman57]

Center consolidating farther south than estimated overnight. Yesterday's G-IV soundings in advance of Isaac have made the models all come into alignment pretty well (Euro, GFS, Canadian). All agree on high pressure holding firm over Texas next week with another center east of the U.S. Coast. Weakness is between SE LA and the eastern FL Panhandle. My initial estimate of the western FL Panhandle for final landfall looks good for now. Don't see any threat to Houston.

[srainhoutx]

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
900 AM EDT FRI AUG 24 2012

VALID 12Z TUE AUG 28 2012 - 12Z FRI AUG 31 2012

...ISAAC EXPECTED TO MOVE INTO THE MID-SOUTH BY NEXT FRIDAY...

THE WESTERLIES ACROSS THE NORTHERN PACIFIC ARE NORTH OF WHAT IS
NORMAL FOR LATE AUGUST. THIS FORCES ENERGY TO POOL DOWNSTREAM,
ACROSS THE PACIFIC NORTHWEST, WITH DOWNSTREAM TROUGHING EXPECTED
ACROSS THE NORTHEAST AND A WARM CORE RIDGE EXPECTED TO WAVER IN
POSITION AND STRENGTH BETWEEN THE CENTRAL ROCKIES AND CENTRAL
PLAINS. THE DETERMINISTIC AND ENSEMBLE MEAN GUIDANCE IS IN GOOD
AGREEMENT ON THESE GENERAL IDEAS. THE MODEL CHOICE THIS PERIOD
WAS PARTIALLY CONSTRAINED BY THE LATEST NATIONAL HURRICANE CENTER
(NHC) FORECAST FOR ISAAC, WHICH RESEMBLED A 00Z ECMWF/00Z GFS/00Z
UKMET COMPROMISE THROUGH WEDNESDAY MORNING. A 00Z GFS/00Z ECMWF
COMPROMISE WAS USED THEREAFTER TO COMPROMISE BETWEEN THE 17Z
COORDINATION CALL FROM THURSDAY AND THE LATEST NHC TRACK FORECAST.
THE 06Z GFS SOLUTION HAD TO BE THROWN OUT BY DEFAULT. THIS LED TO
REASONABLE CONTINUITY WITH THE EARLY MORNING PRESSURES.

TROPICAL CYCLONE ISAAC
======================
THE 06Z GFS RECURVES THE SYSTEM QUICKER THROUGH THE MID-ATLANTIC
STATES THAN THE OTHER GUIDANCE, WHILE THE 00Z ECMWF AND ITS
ENSEMBLE MEAN SHOW STRONGER RIDGING ACROSS THE PLAINS/MIDWEST
WHICH KEEPS THE SYSTEM ON A SLOWER AND MORE WESTERLY TRAJECTORY.
THE 06Z GFS SOLUTION CANNOT BE RULED OUT AS THE PREFERRED MODEL
BLEND DROPS ENERGY FROM THE WESTERLIES AROUND THE NORTHWEST SIDE
OF ISAAC, CLOSING OFF A MID TO UPPER LEVEL LOW ACROSS TEXAS BY
NEXT FRIDAY. THIS DEVELOPMENT WOULD EFFECTIVELY SHIFT THE COL IN
THE STEERING PATTERN SO FAR SOUTH THAT ISAAC WOULD HAVE LITTLE
CHOICE BUT TO RECURVE AROUND THE PERIPHERY OF THE SUBTROPICAL
RIDGE, INITIALLY LURED BY A BREAK IN THE RIDGE ACROSS THE UPPER
OHIO VALLEY TUESDAY (SIMILAR TO DEBBY IN LATE JUNE BUT FARTHER TO
THE WEST). HEAVY CORE RAINFALL WITH AREAL AVERAGE AMOUNTS OF 8-9
INCHES ARE EXPECTED ACROSS SOUTHERN FLORIDA/THE FLORIDA KEYS/THE
WESTERN FLORIDA PANHANDLE WITH THE SYSTEM THROUGH WEDNESDAY
MORNING PER THE 09Z NHC TRACK, WITH LESSER AMOUNTS OF 3-5 INCHES
POSSIBLE ACROSS THE SOUTHEAST AND MID-SOUTH BY NEXT FRIDAY NEAR
ITS TRACK, ITS DRAPING FRONTAL BOUNDARY ACROSS THE SOUTHEAST, AND
WITHIN ITS MAIN INFLOW BAND FROM THE GULF OF MEXICO ON ITS EASTERN
SIDE. LOCAL AMOUNTS OF 12-16 INCHES ARE POSSIBLE BOTH WITHIN ITS
CENTRAL DENSE OVERCAST (CDO) AND WHERE ITS MAIN INFLOW BAND SETS
UP AND PIVOTS, WHICH COULD BE AS FAR EAST AS GEORGIA. THE CURRENT
SIZE AND FORECAST TRACK FOR ISAAC RESEMBLE HURRICANE DENNIS OF
2005. CENTRAL GEORGIA REMAINS IN AN EXCEPTIONAL, LONG-DURATION
DROUGHT SO THEY COULD USE THE RAINFALL. NORTHEAST FLORIDA AND
SOUTHERN GEORGIA WERE SATURATED FROM BERYL AND DEBBY AS WELL AS
SYNOPTICALLY-DRIVEN RAINFALL EVENTS DURING THE PAST SEVERAL DAYS,
SO THE RAIN WOULD BE PROBLEMATIC IN THAT AREA.



ROTH

[srainhoutx]

The outflow has improved at the upper levels as the 'center' attempts to consolidate. Classic signs of a maturing tropical system.

[wxman57]

Looks pretty on satellite now. Maybe we'll have a single well-defined center soon.

[Texas Pirate]

Gotta agree, very beautiful looking. But they all are when you're not the apple of their eye.

[biggerbyte]

Current visual shows absolutely no northerly component in movement. I suppose a wnw movement might be difficult to detect without a grid, but I do not buy a NW trajectory. Going to need the NHC to establish position and movement a couple more times.