WDPS31 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (GABRIELLE) 
WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.3S 159.6E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 367 NM WEST-SOUTHWEST OF NOUMEA, NEW
CALEDONIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 22 KTS
   SIGNIFICANT WAVE HEIGHT: 37 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AGAINST ALL ODDS AND IN THE FACE OF SHARPLY INCREASED NORTHWESTERLY
SHEAR, ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI), A SERIES OF
RECENT MICROWAVE IMAGERY AND RECENT SCATTEROMETER AND SMAP PASSES,
INDICATE THAT TC 12P (GABRIELLE) HAS INTENSIFIED. HOWEVER, THE PEAK
HAS PROBABLY BEEN REACHED AND THE SYSTEM NOW FACES A RAPID
TRANSITION TO A SUBTROPICAL LOW. THE MSI AND ENHANCED INFRARED
(EIR) IMAGERY INDICATES THE SYSTEM REMAINS DEVOID OF A DISTINCT EYE
FEATURE, EVEN NOW AT ITS PEAK. HOWEVER, MICROWAVE IMAGERY THROUGH
THE DAY HAS SHOWN CONSISTENT LOW-LEVEL EYE FEATURES, WITH THE
SMALLEST, BEST DEFINED MICROWAVE EYE IN THE MOST RECENT 100527Z
SSMIS 37GHZ IMAGE. THE STRONGEST CONVECTION REMAINS DOWNSHEAR, IN
THE SOUTHEASTERN QUADRANT, BUT THE EYEWALL REMAINS FIRM ON THE
NORTHWEST SIDE, FOR NOW. THE INITIAL INTENSITY HAS BEEN INCREASED
TO 90 KNOTS, WHICH IS ABOVE ALL THE OBJECTIVE ESTIMATES BUT IN LINE
WITH THE SUBJECTIVE ESTIMATES. THE ADT IS T5.3 (97 KTS), THE AIDT
IS 87 KTS AND THE SATCON IS 96 KTS AND A 100331Z AMSR2 WINDSPEED
ESTIMATE MEASURED 91 KTS IN THE SOUTHEAST QUADRANT, WHICH COMBINED
LENDS HIGH CONFIDENCE TO THE INITIAL INTENSITY. THE SYSTEM IS
MOVING INTO AN INCREASINGLY MARGINAL ENVIRONMENT, WITH SHEAR NOW AT
OR ABOVE 30 KTS, THOUGH IT IS IN PHASE WITH THE STORM MOTION, HENCE
HOW THE SYSTEM HAS BEEN ABLE TO CONTINUE TO INTENSIFY. TC 12P IS IN
THE PROCESS OF CROSSING THE 26C ISOTHERM AND WATER VAPOR IMAGERY
SHOWS A VERY SHARP UPPER-LEVEL TROUGH, WITH VERY DRY AIR TRAILING
THE TROUGH AXIS, JUST TO THE WEST.  THE SYSTEM IS ALREADY STARTING
THE VERY EARLY STAGES OF SUBTROPICAL TRANSITION AS IT RACES OFF TO
THE SOUTHEAST ALONG THE STRENGTHENING GRADIENT BETWEEN THE
SUBTROPICAL RIDGE (STR) TO THE EAST AND THE TROUGH TO THE WEST.

INITIAL WIND RADII BASIS: AMSR2 DATA AND PERSISTENCE. 

CURRENT STEERING MECHANISM: STRONG GRADIENT BETWEEN THE STR TO THE
EAST AND AN APPROACHING TROUGH TO THE WEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   ABRF: T4.5 - 77 KTS
   CIMSS SATCON: 94 KTS AT 100322Z
   CIMSS ADT: 97 KTS AT 100220Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR IN THE MID TO UPPER-LEVELS
ASSOCIATED WITH THE TROUGH MOVING IN FROM THE WEST. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: HAVING REACHED ITS PEAK AT THE PRESENT
ANALYSIS TIME, TC 12P WILL NOW RAPIDLY WEAKEN AND UNDERGO
SUBTROPICAL TRANSITION (STT). THE SYSTEM WILL CONTINUE TO VERY
RAPIDLY MOVE SOUTHEASTWARD ALONG THE TIGHT GRADIENT BETWEEN THE STR
TO THE EAST AND THE TROUGH NOW ENCROACHING FROM THE WEST. TRACK
SPEEDS ARE ANTICIPATED TO INCREASE FURTHER THROUGH TAU 12 BUT WILL
THEN BEGIN TO SLOW AND TURN A BIT MORE EAST-SOUTHEASTWARD THROUGH
THE END OF THE FORECAST AS THE SYSTEM MOVES UNDER THE UPPER-LEVEL
TROUGH AND INTO A REDUCED STEERING GRADIENT. THE SYSTEM WILL CROSS
THE 26C ISOTHERM IN THE NEXT FEW HOURS AND MOVE INTO STEADILY
COOLER WATERS, ROBBING IT OF THE ENERGY SOURCE IT HAS ENJOYED THE
PAST FEW DAYS. AT THE SAME TIME, THE TROUGH, WHICH HAS AN AXIS
SITTING AT ABOUT 156E WILL RAPIDLY MOVE IN, BRINGING INCREASED
SHEAR AND A WEDGE OF VERY DRY AIR OVER TOP OF THE SYSTEM,
EFFECTIVELY DECAPITATING IT WITHIN THE NEXT 24 HOURS. THE
COMBINATION OF THESE EFFECTS WILL LEAD TO RAPID WEAKENING,
PARTICULARLY IN THE FIRST 24 HOURS. THE SYSTEM IS ALREADY STARTING
THE VERY EARLY PHASES OF STT, AND TRANSITION TO A STORM-FORCE
SUBTROPICAL LOW IS EXPECTED NO LATER THAN TAU 36 AND POTENTIALLY AS
EARLY AS TAU 24. AFTER STT, THE SYSTEM WILL CONTINUE TO TRACK
TOWARDS THE NORTH ISLAND OF NEW ZEALAND AND SOME MODELS SUGGEST
SOME POTENTIAL FOR REINTENSIFICATION AS IT APPROACHES.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE
FORECAST TRACK, WITH MINIMAL SPREAD THROUGH THE FORECAST PERIOD,
LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. INTENSITY
GUIDANCE IS ALSO IN GOOD AGREEMENT ON THE RAPID WEAKENING TREND,
THOUGH AS EXPECTED, THERE IS ABOUT A 15 KNOT SPREAD IN THE
GUIDANCE, REFLECTIVE OF THE DIFFERENT PACE OF WEAKENING IN THE
VARIOUS MODELS. THE HWRF SHOWS THE FASTEST RATE WHILE THE COAMPS-TC
AND DECAY-SHIPS SHOW A SLOWER RATE OF WEAKENING. THE JTWC FORECAST
WEAKENS THE SYSTEM FASTER THAN THE BULK OF THE GUIDANCE, IN LINE
WITH HWRF. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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