ATL: ISAAC - Post-Tropical - Discussion

[northjaxpro]

M. Eye Shape & Diameter: Circular with a diameter of 10 nautical miles (12 statute miles)

Small eyewall and a pretty quick pressure drop of 3mb between center fixes!

Yeah, pressure down now to 1004 mb. Isaac is beginning to intensify.

[RL3AO]

New VDM shows surface and MLC lined up. Must have been what Shuriken was talking about.

[meriland23]

people looking for the biggin this year should hope for slow intensification so it has more reason to keep its westward movement, and subsequently be over open water longer.

[Meso]

Satellite appearance becoming more impressive in every frame, the CDO has constantly been expanding and now sure is quite impressive looking. The eastern side also looks to be filling in a bit better in the last few frames. That combined with the alignment of the circulations and pressure drop seems to indicate Isaac may have finally found his footing properly.

[hurricanes1234]

What did the best track update say?

[SFLcane]

[SFLcane]

Up to 80kts over the bahamas as it approaches SFL.

[northjaxpro]

Isaac now 45 mph in new advisory. No change in the track philosophy from NHC. NHC stated in their forecast discussion that they are now even more confident in the GFS and UKMET solutions of Isaac moving into South Florida by early next week.

[meriland23]

Speed has picked up a wee bit, from 80 to 90 mph future cast

[northjaxpro]

Here is a excerpt from the 5 a.m. discussion from NHC on Isaac

A BROAD MID- TO UPPER-LEVEL TROUGH CURRENTLY LOCATED OVER
THE CENTRAL U.S. FROM THE GREAT LAKES SOUTHWARD TO THE CENTRAL GULF
COAST IS EXPECTED TO DIG SOUTHWARD OVER THE NEXT 24 HOURS BEFORE
MOVING EASTWARD. THIS SHOULD RESULT IN AN EROSION OF THE RIDGE
ACROSS THE EASTERN GULF OF MEXICO AND THE SOUTHEASTERN U.S.
INCLUDING FLORIDA AND THE NORTHWESTERN BAHAMAS. THIS DEVELOPING
WEAKNESS IN THE RIDGE SHOULD ALLOW ISAAC TO TURN NORTHWESTWARD
ACROSS EASTERN AND CENTRAL CUBA BY DAYS 4 AND 5. THE NHC MODEL
GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS EVOLVING SCENARIO WITH
THE ECMWF BEING THE LEFTMOST OF THE MODELS...AND THE GFDL AND HWRF
BEING THE RIGHTMOST OF THE MODELS. GIVEN THE RUN-TO-RUN CONSISTENCY
OF THE GFS AND UKMET MODELS...MORE WEIGHT HAS BEEN PLACED ON THOSE
SOLUTIONS...ESPECIALLY SINCE THEY HAVE A STRONGER AND VERTICALLY
DEEPER CYCLONE DEPICTED IN THE MODELS.

[meriland23]

when is 06z gfs run?

[meriland23]

Here is a excerpt from the 5 a.m. discussion from NHC on Isaac

A BROAD MID- TO UPPER-LEVEL TROUGH CURRENTLY LOCATED OVER
THE CENTRAL U.S. FROM THE GREAT LAKES SOUTHWARD TO THE CENTRAL GULF
COAST IS EXPECTED TO DIG SOUTHWARD OVER THE NEXT 24 HOURS BEFORE
MOVING EASTWARD. THIS SHOULD RESULT IN AN EROSION OF THE RIDGE
ACROSS THE EASTERN GULF OF MEXICO AND THE SOUTHEASTERN U.S.
INCLUDING FLORIDA AND THE NORTHWESTERN BAHAMAS. THIS DEVELOPING
WEAKNESS IN THE RIDGE SHOULD ALLOW ISAAC TO TURN NORTHWESTWARD
ACROSS EASTERN AND CENTRAL CUBA BY DAYS 4 AND 5. THE NHC MODEL
GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS EVOLVING SCENARIO WITH
THE ECMWF BEING THE LEFTMOST OF THE MODELS...AND THE GFDL AND HWRF
BEING THE RIGHTMOST OF THE MODELS. GIVEN THE RUN-TO-RUN CONSISTENCY
OF THE GFS AND UKMET MODELS...MORE WEIGHT HAS BEEN PLACED ON THOSE
SOLUTIONS...ESPECIALLY SINCE THEY HAVE A STRONGER AND VERTICALLY
DEEPER CYCLONE DEPICTED IN THE MODELS.

HPC Models Diagnostic Discussion

...SHORTWAVE TROUGH ENTERING THE NORTHERN ROCKIES...

PREFERENCE: AFTER 12Z THU...ECMWF

THE GFS SUFFERS FROM CONVECTIVE GRID-SCALE FEEDBACK BEGINNING
THURSDAY OVER THE NORTHERN PLAINS AND UPPER MIDWEST...CONTRIBUTING
TO A SUSPICIOUSLY FAST SOLUTION...WHILE THE NAM LIES NEAR THE DEEP
EDGE OF THE GUIDANCE WITH ITS ACCOMPANYING SURFACE LOW OVER THE
DAKOTAS ON THURSDAY. GIVEN THESE LOW PROBABILITY OUTCOMES...AND
THAT THE ECMWF HAS SUPPORT FROM THE UKMET AND A LARGE NUMBER OF
GLOBAL ENSEMBLE MEMBERS...THE PREFERENCE IS FOR THE ECMWF.




hmmmm which to believe? I am all types of confuzzled

[northjaxpro]

Recon now reporting pressure down now to 1003 mb. Isaac definitely getting better stacked and organizing rather well at the current time.

[chris_fit]

From The Melbourne Weather Service - Regarding Isaac


AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MELBOURNE FL
351 AM EDT WED AUG 22 2012

..........

SUN-TUE...ATTENTION TOWARD ISAAC DURING THE WEEKEND TRANSLATES TO
HIS POSSIBLE EFFECTS ON AREA EARLY NEXT WEEK. NHC FORECAST DAY 5
POSITION CURRENTLY JUST NORTH OF THE CENTRAL CUBA COAST SUNDAY EVE
WITH ANTICIPATED DRAWING NWD OF THE FORECAST TRACK DUE TO
INTERACTION WITH US EAST COAST TROUGH. UNCERTAINTY EXISTS WITH
REGARD TO STRENGTH OF THE MID TROPOSPHERIC RIDGE CURRENTLY NORTH OF
ISAAC AND THE EVENTUAL WEAKENING OF THE WWD EXTENT OF THE RIDGE AND
ONSET OF INTERACTION WUTH THE US EAST COAST TROUGH. LATEST 00Z ECMWF
RUN INDICATES A STRONGER MORE EXPANSIVE WWD EXTENSION OF THIS RIDGE
AND THUS A MORE WWD MOTION OF ISAAC TOWARD THE EASTERN GULF. IT IS
HOPED THE HIGH ALTITUDE G4 SURVEILLANCE FROM THE NOAA JET BEGINNING
THURSDAY WILL SAMPLE THE REGION AROUND ISAAC AND PROVIDE ADT`L INFO
FOR MODEL GUIDANCE.

[northjaxpro]

Here is a excerpt from the 5 a.m. discussion from NHC on Isaac A BROAD MID- TO UPPER-LEVEL TROUGH CURRENTLY LOCATED OVER THE CENTRAL U.S. FROM THE GREAT LAKES SOUTHWARD TO THE CENTRAL GULF COAST IS EXPECTED TO DIG SOUTHWARD OVER THE NEXT 24 HOURS BEFORE MOVING EASTWARD. THIS SHOULD RESULT IN AN EROSION OF THE RIDGE ACROSS THE EASTERN GULF OF MEXICO AND THE SOUTHEASTERN U.S. INCLUDING FLORIDA AND THE NORTHWESTERN BAHAMAS. THIS DEVELOPING WEAKNESS IN THE RIDGE SHOULD ALLOW ISAAC TO TURN NORTHWESTWARD ACROSS EASTERN AND CENTRAL CUBA BY DAYS 4 AND 5. THE NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS EVOLVING SCENARIO WITH THE ECMWF BEING THE LEFTMOST OF THE MODELS...AND THE GFDL AND HWRF BEING THE RIGHTMOST OF THE MODELS. GIVEN THE RUN-TO-RUN CONSISTENCY OF THE GFS AND UKMET MODELS...MORE WEIGHT HAS BEEN PLACED ON THOSE SOLUTIONS...ESPECIALLY SINCE THEY HAVE A STRONGER AND VERTICALLY DEEPER CYCLONE DEPICTED IN THE MODELS.

HPC Models Diagnostic Discussion ...SHORTWAVE TROUGH ENTERING THE NORTHERN ROCKIES... PREFERENCE: AFTER 12Z THU...ECMWF THE GFS SUFFERS FROM CONVECTIVE GRID-SCALE FEEDBACK BEGINNING THURSDAY OVER THE NORTHERN PLAINS AND UPPER MIDWEST...CONTRIBUTING TO A SUSPICIOUSLY FAST SOLUTION...WHILE THE NAM LIES NEAR THE DEEP EDGE OF THE GUIDANCE WITH ITS ACCOMPANYING SURFACE LOW OVER THE DAKOTAS ON THURSDAY. GIVEN THESE LOW PROBABILITY OUTCOMES...AND THAT THE ECMWF HAS SUPPORT FROM THE UKMET AND A LARGE NUMBER OF GLOBAL ENSEMBLE MEMBERS...THE PREFERENCE IS FOR THE ECMWF. hmmmm which to believe? I am all types of confuzzled

I am inclined to believe NHC and side with GFS and UKMET solutions. GFS has been very consistent the past several days in locking in on a stronger tropical cyclone which would definitely feel the weakness as opposed to a weaker cyclone which EURO keeps insisting, which is a pure outlier with the present trends. Things can certainly change, but at this time, I think the crew at the NHC has a good handle on this.

__________________

The posts in this forum are NOT official forecast. They are just the opinion of this poster. For official information, please refer to the NHC and NWS products

[Shuriken]

hmmmm which to believe? I am all types of confuzzled

Err on the side of climatology: major hurricanes, especially large Cape Verde hurricanes at lower latitude in the Caribbean, have a marked tendency to plow straight ahead -- the models be damned.

[Gustywind]

000
WTNT34 KNHC 220900
TCPAT4

BULLETIN
TROPICAL STORM ISAAC ADVISORY NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
500 AM AST WED AUG 22 2012

...ISAAC GETTING BETTER ORGANIZED...WATCHES AND WARNINGS ISSUED FOR
THE DOMINICAN REPUBLIC...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...15.5N 57.3W
ABOUT 280 MI...445 KM E OF GUADELOUPE
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...W OR 270 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...1003 MB...29.62 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

THE GOVERNMENT OF THE DOMINICAN REPUBLIC HAS ISSUED A HURRICANE
WATCH FOR THE SOUTH COAST OF DOMINICAN REPUBLIC FROM ISLA SAONA
WESTWARD TO THE HAITI-DOMINICAN REPUBLIC SOUTHERN BORDER.

THE GOVERNMENT OF THE DOMINICAN REPUBLIC HAS ISSUED A TROPICAL
STORM WATCH FOR THE NORTH COAST OF DOMINICAN REPUBLIC FROM THE
HAITI-DOMINICAN REPUBLIC NORTHERN BORDER EASTWARD TO NORTH OF
ISLA SAONA.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* MARTINIQUE
* DOMINICA
* GUADELOUPE AND THE SURROUNDING ISLANDS...AND ST. MARTIN
* ST. KITTS...NEVIS...ANTIGUA...BARBUDA...MONTSERRAT...AND ANGUILLA
* SABA...ST. EUSTATIUS...AND ST. MAARTEN
* BRITISH VIRGIN ISLANDS
* PUERTO RICO...VIEQUES...CULEBRA...AND THE U.S. VIRGIN ISLANDS

A HURRICANE WATCH IS IN EFFECT FOR...
* PUERTO RICO...VIEQUES...CULEBRA...AND THE U.S. VIRGIN ISLANDS
* SOUTH COAST OF DOMINICAN REPUBLIC FROM ISLA SAONA WESTWARD TO THE
HAITI-DOMINICAN REPUBLIC SOUTHERN BORDER

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* NORTH COAST OF DOMINICAN REPUBLIC FROM THE HAITI-DOMINICAN
REPUBLIC NORTHERN BORDER EASTWARD TO NORTH OF ISLA SAONA

[Gustywind]

Increasing numbers for Isaac...

22/0545 UTC 15.3N 56.4W T2.5/2.5 ISAAC
21/2345 UTC 15.4N 55.1W T2.0/2.0 ISAAC

[NDG]

Had this been a year ago or better yet 2 to 4 years ago I would had been inclined with the Euro heavely. But for some reason it is not doing too well this year so far with too many inconsistencies in its medium range forecast. It did horribly with Debby and Helene in the GOM, this might be another case with Isaac.

[NDG]

Recon now found a pressure of 1000mb in an area NW from the last fix, might be the true LLC of Isaac, a bit further north near 15.8N