WDPS31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 15P (FIFTEEN) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.4S 165.9E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 162 NM NORTH OF NOUMEA, NEW CALEDONIA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 15P WITH A LARGE AREA OF DEEP CONVECTION OBSCURING AN
ELONGATED LOW-LEVEL CIRCULATION CENTER. A 020950Z ASCAT-B IMAGE
REVEALS THE ELONGATED SIGNATURE OF THE WIND FIELD WITH A BROAD AREA
OF 35-40 KNOT WINDS WITHIN THE SOUTHERN PERIPHERY. THE ASCAT SEEMED
TO HAVE TROUBLE RESOLVING SOME OF THE WIND DIRECTIONS, CAUSING THE
POSITION TO BE ASSESSED WITH LOW CONFIDENCE. ENVIRONMENTAL ANALYSIS
INDICATES THAT 15P IS IN A MARGINAL ENVIRONMENT CHARACTERIZED BY
STRONG POLEWARD AND EQUATORWARD OUTFLOW, HIGH (25-30 KTS) VERTICAL
WIND SHEAR, AND WARM (25-30 C) SEA SURFACE TEMPERATURES. THE
INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE MENTIONED ASCAT IMAGE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE EAST-NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT ALONG THE NORTHERN AND
WESTERN PERIPHERIES OF THE SYSTEM.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 15P IS FORECAST TO TRACK TOWARDS THE
SOUTHEAST, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR THROUGHOUT
THE FORECAST PERIOD. THE MARGINAL ENVIRONMENT IS EXPECTED TO
PERSIST, CAUSING 15P TO STRUGGLE TO FURTHER CONSOLIDATE. AS A
RESULT, 15P IS FORECAST TO SLIGHTLY INTENSIFY TO 45, THEN MAINTAIN
THAT INTENSITY THROUGH TAU 36. AFTER TAU 36, SIGNIFICANT DRY AIR
ENTRAINMENT WILL CAUSE 15P TO WEAKEN. A DROP TO 30 KTS IS FORECAST
TO OCCUR AROUND TAU 72, AS THE SYSTEM PASSES SOUTHWEST OF FIJI.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE TRACK OF 15P WITH A 90 NM CROSS-TRACK SPREAD AT TAU
72. THAT IS WITH RULING OUT THE MAIN OUTLIER, GALWEM, WHICH HAS A
DRASTICALLY SLOWER TRACK SPEED THAN THE REMAINDER OF GUIDANCE. THE
JTWC TRACK FORECAST IS PLACED SLIGHTLY FASTER THAN CONSENSUS WITH
HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN WORSE AGREEMENT,
PARTICULARLY COAMPS-TC, WHICH HAS THE SYSTEM CONTINUING TO
INTENSIFY TO AROUND 60 KTS AT TAU 60. GFS AND HAFS-A AGREE THAT THE
SYSTEM WILL MAINTAIN INTENSITY THROUGH TAU 36 AND THEN BEGIN TO
WEAKEN. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO HAFS-A AND
GFS WITH MEDIUM CONFIDENCE. 

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