WDPS33 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (TWELVE) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.1S 166.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 120 NM WEST-NORTHWEST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
EXTREMELY WEAK SYSTEM, WITH SCATTERED DISORGANIZED CONVECTION
FLARING IN MULTIPLE SECTORS OF THE CIRCULATION. TROPICAL CYCLONE
(TC) 12P (TWELVE) CONTINUES TO STRUGGLE IN THE FACE OF PERSISTENT
NORTHWESTERLY SHEAR, THE INFLUENCE OF DRY MID-LEVEL AIR, AND A
HIGHLY ASYMMETRIC VORTEX. A 091203Z GMI 37GHZ MICROWAVE IMAGE
REVEALED A BROAD AND ILL-DEFINED LOW EMISSIVITY REGION (LER),
DENOTING THE OUTLINES OF THE OVERALL CIRCULATION. THE INITIAL
POSITION WAS PLACED IN THE SOUTHEASTERN CORNER OF THIS LER, CLOSE
TO THE AREA OF SHARPEST TURNING IN THE LOW-LEVEL BANDING FEATURES.
CONFIDENCE IN THE INITIAL POSITION REMAINS LOW HOWEVER, DUE TO THE
OBSCURED NATURE OF THE LOW-CLOUD FIELD IN THE SHORTWAVE INFRARED
(SWIR) AND PROXY VISIBLE IMAGERY. THE INITIAL INTENSITY IS
GENEROUSLY HELD AT 35 KNOTS BASED ON THE SUBJECTIVE AND OBJECTIVE
INTENSITY ESTIMATES NOTED BELOW AND A PARTIAL 091114Z ASCAT-C PASS
WHICH SHOWED WINDS OF 30-34 KNOTS IN THE FAR WESTERN PORTIONS OF
THE CIRCULATION, SUGGESTING SOME HIGHER WINDS COULD BE LURKING
CLOSER INTO THE CENTER. THE ENVIRONMENT CONTINUES TO BE MARGINAL
AT BEST, WITH RELATIVELY MODERATE DEEP-LAYER SHEAR, STRONG POLEWARD
AND EASTWARD OUTFLOW AND WARM SSTS, OFFSET BY THE CONTINUED
PRESENCE OF DRY MID-LEVEL AIR TO THE WEST.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN RIM OF A DEEP-LAYER NEAR
EQUATORIAL RIDGE (NER) CENTERED TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS SATCON: 39 KTS AT 091200Z
   CIMSS ADT: 37 KTS AT 091130Z
   CIMSS DPRINT: 33 KTS AT 091200ZZ

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR TO THE WEST

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING. THE FORECAST IS HOWEVER
TRUNCATED TO 72 HOURS WITH THIS FORECAST. 

FORECAST DISCUSSION: TC 12P WILL TRACK EAST-SOUTHEASTWARD ALONG THE
TIGHT GRADIENT FLOW BETWEEN A DEEP-LAYER NER CENTERED TO THE
NORTHEAST AND A DEEP TROUGH TO THE SOUTHWEST FOR THE NEXT 24 TO 36
HOURS. AFTER TAU 36, THE NER WILL BUILD SOUTHWESTWARD, EVENTUALLY
PINCHING OFF INTO A SEPARATE SUBTROPICAL RIDGE (STR) WHICH WILL
THEN QUICKLY TRANSIT WESTWARD. THE DEVELOPMENT OF THIS STR WILL
HAVE THE EFFECT OF SLOWING THE EASTWARD PROGRESSION OF TC 12P, WITH
THE SYSTEM ULTIMATELY BECOMING QUASI-STATIONARY BY THE END OF THE
FORECAST AS THE STR MOVES INTO POSITION DUE EAST OF TC 12P. IN
TERMS OF INTENSITY, LITTLE TO NO CHANGE IN THE INTENSITY IS
EXPECTED FOR THE NEXT 12 TO 24 HOURS AS THE ENVIRONMENTAL
CONDITIONS REMAIN RELATIVELY STAGNANT. A BRIEF RESPITE FROM THE
MODERATE SHEAR IS ANTICIPATED TO BEGIN BY TAU 24, WHICH WILL ALLOW
FOR A SHORT PERIOD OF INTENSIFICATION. BUT THE PARTY WILL BE
SHORT-LIVED, AS SHEAR WILL INCREASE SHARPLY AND USHER IN A MUCH
DRIER AIR MASS AFTER TAU 36. THE COMBINED EFFECTS OF THE INCREASED
SHEAR AND DRY AIR WILL INDUCE RAPID WEAKENING, WITH TC 12P EXPECTED
TO DISSIPATE OVER WATER NO LATER THAN TAU 72. 

MODEL DISCUSSION: THROUGH TAU 36, DETERMINISTIC TRACK GUIDANCE IS
IN GOOD AGREEMENT, DISPLAYING MINIMAL CROSS AND ALONG-TRACK SPREAD.
BUT EVEN AS EARLY AS TAU 48, THE MODELS BEGIN TO RAPIDLY DIVERGE,
BOTH IN TRACK SPEED AND IN TRACK DIRECTION. SIMILAR TO THE LAST
MODEL RUN, THE MODELS ARE SPLIT INTO THREE CAMPS AFTER TAU 48. THE
US MODELS SLOWLY TURN THE SYSTEM TO THE NORTH, THE GALWEM AND
NAVGEM RACE THE SYSTEM STRAIGHT AHEAD TO A POSITION SOUTH OF FIJI
WHILE THE EUROPEAN MODELS TURN THE SYSTEM SOUTHWARD AND THEN
SOUTHWESTWARD. THE DIVERGENCE IS SUCH THAT CROSS-TRACK SPREAD
INCREASES TO 175NM AND ALONG-TRACK SPREAD INCREASES TO OVER 350NM
BY TAU 72. THE JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN WITH
LOW CONFIDENCE. INTENSITY GUIDANCE REMAINS SPLIT, WITH THE SHIPS
(NAVGEM AND GFS) CONTINUING TO SHOW STEADY INTENSIFICATION, WHILE
THE REMAINDER OF THE MODEL GUIDANCE SHOWS A ROUGHLY STEADY-STATE
INTENSITY THROUGH TAU 36 FOLLOWED BY WEAKENING TO DISSIPATION
AROUND TAU 72. THE JTWC FORECAST IS CONSISTENT WITH THE HAFS-A BUT
CONFIDENCE REMAINS LOW.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   INTENSITY 0 - 72 HR: LOW//
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