WDPS31 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 23P (TWENTYTHREE) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.2S 167.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 38 NM SOUTHWEST OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 23P WITH PERSISTENT DEEP CONVECTION OBSCURING THE LOW-LEVEL
CIRCULATION CENTER (LLCC) AND FRAGMENTED BANDING ALONG THE EASTERN
SEMICIRCLE. A 261807Z F17 SSMIS 91 GHZ MICROWAVE IMAGE REVEALED
THAT THE DEEPEST CONVECTION IS SLIGHTLY OFFSET TO THE SOUTH OF THE
ASSESSED CENTER. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE SSMIS IMAGE AND ANIMATED EIR IMAGERY. THE
INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED PRIMARILY ON THE AGENCY DVORAK FIXES AGREEING ON T2.5 (35
KTS). ENVIRONMENTAL ANALYSIS INDICATES THAT 23P IS IN A HIGHLY
FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW
ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (28-29 C) SEA
SURFACE TEMPERATURES (SST).

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) CENTERED OVER FIJI

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   NFFN: T2.5 - 35 KTS
   CIMSS D-PRINT: 42 KTS AT 261800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 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: TC 23P IS FORECAST TO TRACK EAST-SOUTHEASTWARD, 
ALONG THE SOUTHWESTERN PERIPHERY OF THE STR THROUGH TAU 48. NEAR TAU 
48, THE RIDGE IS EXPECTED TO PROPAGATE EASTWARD AND REORIENT INTO A 
NORTHWEST-SOUTHEAST ORIENTATION, FURTHER GUIDING THE VORTEX 
SOUTHEASTWARD THROUGH TAU 72. REGARDING INTENSITY, 23P IS FORECAST TO 
STEADILY INTENSIFY THROUGH TAU 48 AS THE ENVIRONMENT REMAINS FAVORABLE 
WITH LOW SHEAR, STRONG POLEWARD OUTFLOW, AND WARM SST. THE PEAK 
INTENSITY IS CURRENTLY FORECAST TO BE AROUND 65 KTS, HOWEVER, THE 
SMALL INNER-CORE OF THE SYSTEM COULD POTENTIALLY ALLOW FOR A MORE 
RAPID RATE OF INTENSIFICATION. AFTER TAU 48, NORTHWESTERLY SHEAR IS 
EXPECTED TO QUICKLY INCREASE AND DRY AIR ENTRAINMENT FROM THE WEST 
WILL BEGIN TO IMPACT THE SYSTEM. THESE TWO FACTORS WILL PUT A CAP ON 
THE INTENSIFICATION TREND. BY TAU 60, NORTHWESTERLY SHEAR IS FORECAST 
TO BE NEAR 40 KTS, WHICH WILL ULTIMATELY CAUSE THE SYSTEM TO WEAKEN TO 
AROUND 55 KTS AT TAU 72.  SUBTROPICAL TRANSITION (STT) IS FORECAST TO 
BEGIN NEAR TAU 48 WITH COMPLETION NO LATER THAN TAU 72 AS THE VORTEX
SHALLOWS, ELONGATES, AND BECOMES EMBEDDED WITHIN THE STRONG
UPPER-LEVEL FLOW. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH A CROSS-TRACK SPREAD
OF 90 NM AT TAU 72. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE
MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE
AGREES ON INTENSIFICATION THROUGH TAU 48 BEFORE WEAKENING. RIDE (A
RAPID INTENSIFICATION AID) HAS TRIGGERED THIS MODEL RUN, AND IS A
MAJOR OUTLIER, SUGGESTING AN INTENSITY OF 105 KTS AT TAU 48. THE
REST OF GUIDANCE IS SITUATED WITHIN A SMALL ENVELOPE OF 50-70 KTS
AT TAU 48. THE JTWC INTENSITY FORECAST IS PLACED NEAR THE CONSENSUS
WITH MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM//
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