WDPS31 PGTW 270300
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: 12.6S 171.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 346 NM NORTH-NORTHEAST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD
CONSOLIDATING SYSTEM WITH SPIRAL BANDS OF DEEP CONVECTION WRAPPING
INTO A PERSISTENT CONVECTIVE CLOUD STRUCTURE. THE INITIAL POSITION
IS ASSESSED WITH HIGH CONFIDENCE BASED ON A BULLSEYE 262222Z
ASCAT-B PASS. THE INITIAL INTENSITY IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE IMPROVING CONVECTIVE STRUCTURE AS WELL AS A
COMBINATION OF AGENCY DVORAK INTENSITY ESTIMATES AND THE
AFOREMENTIONED ASCAT-B WHICH SHOWS UP TO 35 KNOTS ON THE EASTERN
QUADRANT. THE OVERALL ENVIRONMENT IS ASSESSED AS FAVORABLE BASED ON 
MODERATE RADIAL OUTFLOW LOW TO MODERATE (10-15 KNOTS) VERTICAL WIND 
SHEAR (VWS) AND WARM (30-31C) SEA SURFACE TEMPERATURES (SSTS).

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
EAST-SOUTHEAST. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 15P IS FORECAST TO TRACK SOUTHWESTWARD AND
TRANSIT THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE IN A
FAVORABLE ENVIRONMENT AS THE CYCLONE NEARS PORT VILA, VANUATU.
ENVIRONMENTAL CONDITIONS OVER THE NEXT 36-48 HOURS WILL REMAIN
FAVORABLE, CHARACTERIZED BY WARM SEA SURFACE TEMPERATURES (SSTS)
(30-31C), MODERATE DIVERGENCE ALOFT AND LOW-MODERATE VERTICAL WIND
SHEAR (VWS) (10-15 KNOTS). THESE FAVORABLE CONDITIONS WILL FUEL A
SIGNIFICANT INTENSIFICATION TREND TO ALLOW 15P TO REACH A POTENTIAL
MAXIMUM INTENSITY OF 80 KNOTS, POSSIBLY HIGHER, BY TAU 48. HOWEVER,
BETWEEN TAU 48 AND TAU 72 INCREASING VWS AND DRY AIR INFLUX WILL
BEGIN TO WEAKEN THE SYSTEM. BY TAU 96, TC 15P WILL BEGIN
SUBTROPICAL TRANSITION AS THE SYSTEM CROSSES THE 26C ISOTHERM AND
TRANSITIONS TO A SHALLOW, ASYMMETRIC WARM CORE WITH AN EXPANSIVE
WIND FIELD. 


MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT THROUGH
TAU 36 WITH ONLY A 70NM SPREAD IN SOLUTIONS. HOWEVER, PAST TAU 36,
THE UKMET DETERMINISTIC AND ENSEMBLE MEAN, ALONG WITH THE GALWEM
REPRESENT THE WESTERN EDGE OF THE GUIDANCE ENVELOPE. WHILE THE GFS
AND ECMWF AND THEIR ENSEMBLE MEANS REPRESENT THE EASTERN EDGE OF
GUIDANCE. THEREFORE, THE JTWC FORECAST FOLLOWS CLOSE TO THE
MULTI-MODEL CONSENSUS THROUGH TAU 36, AND HEDGED CLOSER TO THE GFS
AND ECMWF SOLUTIONS THROUGH TAU 72. AFTER TAU 72, THE TRACK
CONFIDENCE IS MEDIUM AS THE SPREAD WIDENS. THE INTENSITY GUIDANCE
IS IN GOOD AGREEMENT WITH ALL MEMBERS SHOWING STEADY
INTENSIFICATION THROUGH TAU 48 WITH THE POSSIBILITY FOR A DRAMATIC
INTENSIFICATION TREND. AFTER TAU 48, INTENSITY MODELS DIVERGE WITH
THE HWRF SHOWING A PEAK INTENSITY OF 100 KNOTS, WHILE THE GFS SHOWS
A PEAK OF 60 KNOTS. THUS, THE JTWC INTENSITY FORECAST IS PLACED
WITH MEDIUM CONFIDENCE.       

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