WDPS31 PGTW 220900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (EIGHTEEN) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.4S 149.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 242 NM EAST-NORTHEAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN OBSCURED
LOW-LEVEL CIRCULATION CENTER (LLCC) WITH DEEP CONVECTION SHEARED TO
THE SOUTHEAST OF THE CENTER. LOW-LEVEL CLOUD BANDS ARE EVIDENT IN
THE WESTERN PERIPHERY OF THE CIRCULATION, INDICATING A SLIGHT
SOUTHEASTWARD TILT DUE TO NORTHWESTERLY SHEAR. WATER VAPOR IMAGERY
REVEALS STRONG POLEWARD AND EASTWARD OUTFLOW INTO A JET MAXIMUM.
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
AFOREMENTIONED ANIMATED VISIBLE IMAGERY. THE INITIAL INTENSITY OF
35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY FIXES
LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: A COMPETING ENVIRONMENT BETWEEN AN
EXPANSIVE NEAR EQUATORIAL RIDGE (NER) OVER AUSTRALIA AND A NER TO
THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: A COMPETING STEERING ENVIRONMENT BETWEEN TWO
NERS WILL PERSIST FOR THE FIRST 48 HOURS OF THE FORECAST PUSHING
TROPICAL CYCLONE (TC) 18P EASTWARD. AFTER TAU 48, THE NER TO THE
EAST WILL BECOME THE PRIMARY STEERING MECHANISM, CAUSING TC 18P TO
CURVE SOUTHWARD FOR THE REMAINDER OF THE FORECAST PERIOD. FAVORABLE
CONDITIONS OF LOW VERTICAL WIND SHEAR, STRONG POLEWARD OUTFLOW, AND
WARM SEA SURFACE TEMPERATURES WILL ALLOW TC 18P TO INTENSIFY
THROUGH THE FIRST 72 HOURS OF THE FORECAST TO A PEAK OF 65KTS.
BETWEEN TAU 72 AND TAU 96, VERTICAL WIND SHEAR WILL INCREASE TO
UNFAVORABLE LEVELS ABOVE 20KTS, CAUSING A GRADUAL DECLINE OF
INTENSITY AFTER TAU 96. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE HAS A SIGNIFICANT
SPREAD OF SOLUTIONS WITHIN THE JTWC MULTI-MODEL CONSENSUS.
EXCLUDING THE OUTLIER OF NAVGEM, THE BULK OF THE CONSENSUS MEMBERS
HAS A 134NM CROSS-TRACK SPREAD BY TAU 72 AND A 243NM CROSS-TRACK
SPREAD BY TAU 120. THE COMPETING STEERING ENVIRONMENT CONTRIBUTES
TO THE UNCERTAINTY LEADING SOME MODEL SOLUTIONS, LIKE THE GEFS
ENSEMBLE MEAN, TO CURVE MORE SHARPLY THAN OTHERS, LIKE GFS. THE
JTWC INTENSITY GUIDANCE ALSO REPRESENTS A LARGE SPREAD. THE BULK OF
MEMBERS (JTWC SHIPS, GFS, COAMPS-TC) LIE BETWEEN A PEAK OF
60-70KTS, WHILE HWRF AND HAFS-A INDICATE RAPID INTENSIFICATION
BETWEEN 95-105KTS. TWO RAPID INTENSIFICATION AIDS ALSO HINT AT
POTENTIAL RAPID INTENSIFICATION WITHIN THE FIRST 24 HOURS OF THE
STORM, LEADING TO LOW CONFIDENCE IN THE NEAR- AND LONG-TERM
FORECAST.

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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