WDPS31 PGTW 140900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 30P (THIRTY) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.1S 168.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 156 NM NORTH OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 30P WITH A BROAD AND ASYMMETRICAL WIND FIELD COMPRISED OF
THE STRONGEST WINDS CONFINED TO THE EASTERN SEMICIRCLE. LARGE
SWATHS OF CONVECTION ARE NOW OBSCURING THE CIRCULATION CENTER. A
140446Z SSMIS 91 GHZ MICROWAVE IMAGE REVEALED THE BROAD CONVECTIVE
BANDING PLACED WITHIN THE NORTHERN AND SOUTHERN PERIPHERIES OF THE
SYSTEM. ENVIRONMENTAL ANALYSIS INDICATES THAT 30P IS IN A FAVORABLE
ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD AND EQUATORWARD OUTFLOW
ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA
SURFACE TEMPERATURES. THE MAIN HINDERING FACTOR FOR THE SYSTEM WILL
BE THE ASYMMETRICAL AND BROAD WIND FIELD. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED MSI AND
MENTIONED SSMIS MICROWAVE IMAGE. THE INITIAL INTENSITY OF 35 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES
LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE FROM EARLIER SMAP DATA

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST. 

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

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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: TC 30P IS FORECAST TO TRACK SOUTHWARD, ALONG
THE WESTERN PERIPHERY OF THE STR THROUGHOUT THE FORECAST PERIOD
WITH FASTER THAN AVERAGE TRACK SPEEDS. THE SYSTEM IS EXPECTED TO
STEADILY INTENSIFY OVER THE NEXT 48 HOURS DUE TO THE FAVORABLE
ENVIRONMENT, PARTICULARLY POLEWARD OUTFLOW. NEAR TAU 48, AN
INCOMING LONG WAVE TROUGH WILL ENVELOP THE SYSTEM AND CAUSE THE
SYSTEM TO COMPLETE SUBTROPICAL TRANSITION BY TAU 48 AND
EXTRATROPICAL TRANSITION BY TAU 72. THE COLD-CORE LOW WILL THEN
BECOME STATIONARY PLACED TO THE NORTHWEST OF NEW ZEALAND. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH AN EVEN 230 NM CROSS-TRACK SPREAD AT TAU 48 AND
MINIMAL ALONG-TRACK SPREAD. THE JTWC TRACK FORECAST IS PLACED CLOSE
TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. INTENSITY
GUIDANCE IS ALSO IN GOOD AGREEMENT WITH ALL MODELS SUGGESTING
INTENSIFICATION TO 45-60 KTS AT TAU 48. THEREFORE, THE JTWC
INTENSITY FORECAST IS ALSO PLACED WITH HIGH CONFIDENCE.

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