[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 232055
TCDAT4

TROPICAL STORM ISAAC DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
500 PM AST THU AUG 23 2012

LOCATING THE CENTER OF ISAAC IS A BIT PROBLEMATIC THIS AFTERNOON.
WHILE THE CYCLONE HAS A LARGE AND WELL-DEFINED OUTER
CIRCULATION...THE INNER CORE HAS NOT CONSOLIDATED AND THERE ARE
STILL MULTIPLE VORTICITY CENTERS ROTATING AROUND THE MEAN CENTER.
HIGHLIGHTING THE ISSUE ARE DATA FROM NOAA BUOY 42059...WHICH HAS
REPORTED 25-30 KT SOUTHWESTERLY WINDS AT A POSITION SOUTHWEST OF
THE LATEST HURRICANE HUNTER AIRCRAFT FIXES...WHICH IN TURN WERE
SOUTH OF THE CENTER TRACKED IN THE PREVIOUS ADVISORY.  THE INITIAL
POSITION IS A BLEND OF ALL THESE FEATURES.  THE INITIAL INTENSITY
REMAINS 35 KT BASED ON THE HURRICANE HUNTER DATA.

THE SOMEWHAT UNCERTAIN INITIAL MOTION IS 285/14.  THE TRACK MODEL
GUIDANCE IS IN GOOD AGREEMENT THAT ISAAC SHOULD MOVE GENERALLY
WEST-NORTHWESTWARD FOR THE NEXT 48-72 HR...AND THIS PART OF THE NEW
FORECAST TRACK IS VERY SIMILAR TO THE PREVIOUS TRACK.  AFTER THAT
TIME...THE GUIDANCE HAS SHIFTED A LITTLE WESTWARD IN RESPONSE TO
THE GLOBAL MODELS FORECASTING THE WEAKNESS IN THE SUBTROPICAL RIDGE
TO BE SOMEWHAT FARTHER WEST THAN BEFORE.  THE ECMWF IN PARTICULAR
HAS MADE A SIGNIFICANT SHIFT...SHOWING A WEST-NORTHWESTWARD MOTION
INTO THE CENTRAL GULF OF MEXICO BY DAY 5.  DESPITE THE GENERAL
WESTWARD SHIFT...THE HWRF AND CANADIAN MODELS STILL CALL FOR ISAAC
TO MOVE UP THE FLORIDA PENINSULA.  THUS... SIGNIFICANT UNCERTAINTY
REMAINS ABOUT THE THREAT ISAAC POSES TO FLORIDA AND OTHER PORTIONS
OF THE GULF COAST.  THE 96-120 HR POINTS HAVE BEEN SHIFTED A LITTLE
WESTWARD FROM THE PREVIOUS ADVISORY AND LIE NEAR THE CENTER OF THE
GUIDANCE ENVELOPE AND THE CONSENSUS MODELS.

IN THE SHORT TERM...THE STRUCTURE OF ISAAC SUGGESTS THAT ONLY SLOW
STRENGTHENING IS LIKELY.  HOWEVER...THE ENVIRONMENTAL CONDITIONS
ARE FAVORABLE FOR RAPID INTENSIFICATION...WHICH COULD OCCUR IF THE
CYCLONE DEVELOPS A WELL-DEFINED INNER CORE.  WHILE THE OFFICIAL
FORECAST NO LONGER SHOWS IT...ISAAC COULD REACH HURRICANE INTENSITY
ABOUT THE TIME IT MAKES LANDFALL IN HISPANIOLA BETWEEN 24-36 HR.
AFTER THAT...PASSAGE OVER HISPANIOLA AND CUBA SHOULD CAUSE SOME
WEAKENING. THE INTENSITY FORECAST SHOWS STRENGTHENING OVER THE GULF
OF MEXICO...AND THE CURRENT 120 HR INTENSITY COULD BE CONSERVATIVE
IF THE GLOBAL MODEL UPPER-LEVEL WIND FORECASTS VERIFY.  THE NEW
INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS FORECAST AND REMAINS
STRONGER THAN THE INTENSITY CONSENSUS.

THE NOAA G-IV JET AND AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
ARE CURRENTLY CONDUCTING A SYNOPTIC SURVEILLANCE MISSION AROUND
ISAAC.  THE DATA WILL BE AVAILABLE FOR THE 0000 UTC MODEL RUNS.


FORECAST POSITIONS AND MAX WINDS

INIT  23/2100Z 16.0N  67.1W   35 KT  40 MPH
 12H  24/0600Z 16.6N  69.0W   40 KT  45 MPH
 24H  24/1800Z 17.5N  71.5W   50 KT  60 MPH
 36H  25/0600Z 18.9N  74.0W   60 KT  70 MPH
 48H  25/1800Z 20.3N  76.2W   55 KT  65 MPH...INLAND
 72H  26/1800Z 23.0N  80.0W   50 KT  60 MPH...OVER WATER
 96H  27/1800Z 25.5N  83.0W   65 KT  75 MPH
120H  28/1800Z 28.5N  85.5W   75 KT  85 MPH

$$
FORECASTER BEVEN



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