WDPS33 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (TWELVE) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.8S 163.5E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 298 NM WEST-NORTHWEST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 12P (TWELVE) HAS RAPIDLY COME TOGETHER OVER
THE PAST 12 HOURS, THOUGH IT REMAINS SOMEWHAT ELONGATED AND IS
STILL STRUGGLING TO AXISYMMETRIZE. ANIMATED COMBINATION IMAGERY
(MULTISPECTRAL AND ENHANCED INFRARED) SHOWS THE WESTERN PORTION OF
AN ELONGATED SURFACE CIRCULATION ORIENTED ON A ROUGHLY
NORTHWEST-SOUTHEAST AXIS. THE LOW LEVEL CIRCULATION CENTER (LLCC)
IS OBSCURED, ASSESSED TO BE IN THE FAR EASTERN PORTION OF THE
ELONGATED CIRCULATION. THE LATEST IMAGERY SHOWS A BLOOM OF
SYMMETRICAL DEEP CONVECTION, WHICH LOOKS IMPRESSIVE WITH CLOUD TOP
TEMPERATURES AS LOW AS -97C AND NUMEROUS LIGHTNING STRIKES, THOUGH
IT REMAINS DISPLACED TO THE EAST OF THE LLCC. A 080652Z SSMIS 91GHZ
MICROWAVE IMAGE SHOWED THE WEAK BANDING EFFECTS IN THE DEEP
CONVECTION TO THE EAST, WITH A FALSE MICROWAVE EYE PRESENT IN THE
36GHZ CHANNEL, AND THE EXPOSED LLCC ON THE FAR WESTERN EDGE OF THE
CONVECTIVE MASS. THE INITIAL POSITION WAS ASSESSED WITH LOW
CONFIDENCE, EVEN WITH THE MICROWAVE IMAGERY, DUE TO THE POTENTIAL
FOR MULTIPLE AREAS OF ROTATION BEING EMBEDDED WITHIN THE LARGER,
ELONGATED CIRCULATION. THE INITIAL INTENSITY OF 40 KNOTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN OVERALL ASSESSMENT OF
THE AVAILABLE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES OUTLINED
BELOW. THE SYSTEM IS MOVING SOUTHEASTWARD ALONG THE SOUTHERN SIDE
OF AN EXTENSIVE DEEP-LAYER NEAR-EQUATORIAL RIDGE (NER) CENTERED TO
THE NORTH. ANALYSIS REVEALS A MARGINALLY FAVORABLE ENVIRONMENT,
WITH LOW VWS, AND WARM SSTS AND ROBUST POLEWARD OUTFLOW BEING
OFFSET BY PERSISTENT MODERATE MID-LEVEL SHEAR AND DRY MID-LEVEL
ENTRENCHED ON THE WESTERN SIDE OF THE CIRCULATION.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN SIDE OF A NER CENTERED TO THE
NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS ADT: 39 KTS AT 080530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 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.

FORECAST DISCUSSION: TC 12P IS FORECAST TO CONTINUE TRACKING EAST-
SOUTHEAST ALONG THE STRONG AND EXTENSIVE NER TO THE NORTH THROUGH THE 
BULK OF THE FORECAST PERIOD, AT LEAST THROUGH TAU 72. EFFECTIVE DEEP-
LAYER SHEAR VALUES ARE LIKELY A BIT LOWER THAN CURRENTLY ASSESSED DUE 
TO THE TRACK BEING IN PERFECT PHASE WITH THE SHEAR VECTOR. HOWEVER 
MID-LEVEL SHEAR APPEARS TO BE STRONGER THAN ANTICIPATED, BASED ON GFS 
AND ECMWF MODEL-DERIVED SOUNDINGS. THE LATEST MODEL FIELDS SUGGEST 
THAT THIS HIGHER MID-LEVEL SHEAR WILL PERSIST THROUGH THE ENTIRE 
FORECAST PERIOD. THUS, THE SYSTEM STILL HAS SOME WORK TO DO TO 
SYMMETRIZE THE VORTEX AND THIS WILL LIMIT ANY REALISTIC CHANCES OF 
SIGNIFICANT INTENSIFICATION IN THE NEAR-TERM. THE FORECAST CALLS FOR A 
SLIGHT REDUCTION IN THE SHEAR OVER THE NEXT 24 HOURS WHICH SHOULD 
ALLOW FOR SOME SLIGHT INTENSIFICATION, UP TO 50 KNOTS, BUT THEN THE 
STRONG SHEAR RETURNS AND THE SYSTEM WILL STEADILY WEAKEN THROUGH THE 
REMAINDER OF THE FORECAST. AS IT BEGINS TO DISSIPATE AFTER TAU 72, TC 
12P WILL MOVE INTO A WEAK STEERING ENVIRONMENT, BETWEEN STRONG RIDGING 
BOTH NORTH AND SOUTH OF THE SYSTEM. THE CURRENT FORECAST CALLS FOR THE 
SYSTEM TO SLOW DOWN AND BECOME QUASI-STATIONARY BY THE END OF 
FORECAST, WHILE THE SYSTEM DISSIPATES. A TURN EITHER TO THE NORTH OR 
SOUTH IS POSSIBLE DURING THIS TIME AS THE STEERING BECOMES HIGHLY 
UNCERTAIN. FULL DISSIPATION BELOW THE WARNING THRESHOLD IS EXPECTED NO 
LATER THAN TAU 120.  

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
GOOD AGREEMENT THROUGH THE FIRST 72 HOURS OF THE FORECAST. THE
CONSENSUS GUIDANCE PACKAGE BEGINS TO SHOW INDIVIDUAL MEMBERS
BREAKING OFF FROM THE PACK BY TAU 48, WITH THE GFS FLATTENING OUT
TO A DUE EASTWARD TRACK AFTER THIS POINT, WHILE THE NAVGEM DIVES
MORE SOUTHWARD, LEADING TO A CROSS-TRACK SPREAD OF 185NM BY TAU 72.
AT THIS POINT THINGS GET REALLY SQUIRRELLY, WITH EACH MEMBER OF THE
CONSENSUS GOING OFF TO DIFFERENT POINTS OF THE COMPASS; GFS ENSEMBLE
NORTHWEST, GFS NORTHEAST, GALWEM EAST, NAVGEM QUASI-STATIONARY,
ECMWF WEST, AND UKMET SOUTHWEST. SPREAD AT THIS POINT IS A
MEANINGLESS METRIC, BUT NEEDLESS TO SAY INCREASES SHARPLY. THE JTWC
FORECAST REMAINS CONSISTENT WITH THE CONSENSUS MEAN THROUGH THE
BULK OF THE FORECAST, THOUGH SLOWS DOWN AND BECOMES
QUASI-STATIONARY BY THE END OF THE FORECAST PERIOD. UNCERTAINTY IS
HIGH AND CONFIDENCE IN THE JTWC FORECAST AFTER TAU 72 IS LOW.
INTENSITY GUIDANCE IS MIXED, WITH THE SHIPS (GFS) BEING
EXCEPTIONALLY AGGRESSIVE AND FAR OUTPACING ALL THE OTHERS EXCEPT
FOR THE RIPA, RI45, AND RI25 WHICH ARE ALSO TRIGGERED, THOUGH BASED
ON THE OVERALL ENVIRONMENT, THESE SEEM UNREALISTIC AT BEST. THE
REMAINDER OF THE GUIDANCE SHOWS MINIMAL INTENSIFICATION OR
WEAKENING. THE JTWC FORECAST LIES CLOSE TO THE COAMPS-TC (GFS) FOR
THE MAJORITY OF THE FORECAST, WITH LOW CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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