Tropical Cyclone ROBYN (03S)

WTPS31 PGTW 120300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 08P (PITA) WARNING NR 004//
RMKS/
1. TROPICAL CYCLONE 08P (PITA) WARNING NR 004    
   01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   120000Z --- NEAR 21.9S 158.8W
     MOVEMENT PAST SIX HOURS - 095 DEGREES AT 17 KTS
     POSITION ACCURATE TO WITHIN 025 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   BECOMING SUBTROPICAL
   RADIUS OF 034 KT WINDS - 055 NM NORTHEAST QUADRANT
                            065 NM SOUTHEAST QUADRANT
                            050 NM SOUTHWEST QUADRANT
                            000 NM NORTHWEST QUADRANT
   REPEAT POSIT: 21.9S 158.8W
    ---
   FORECASTS:
   12 HRS, VALID AT:
   121200Z --- 21.9S 156.5W
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   SUBTROPICAL
    ---
REMARKS:
120300Z POSITION NEAR 21.9S 158.2W.
12JAN25. TROPICAL CYCLONE 08P (PITA), LOCATED APPROXIMATELY 70 NM
SOUTHEAST OF RAROTONGA, HAS TRACKED EASTWARD AT 17 KNOTS OVER THE
PAST SIX HOURS. THE CURRENT POSITION IS ASSESSED WITH HIGH
CONFIDENCE IN THE CENTER OF THE EXPOSED LOW-LEVEL CIRCULATION
EVIDENT IN MULTISPECTRAL SATELLITE IMAGERY. THE INTENSITY ESTIMATE
OF 35 KNOTS IS CONSISTENT WITH RECENT SUBJECTIVE DVORAK ANALYSES
FROM MULTIPLE REPORTING AGENCIES AND SUPPORTED BY A 121931Z METOP-C
ASCAT PASS SHOWING 30-35 KNOT WINDS NEAR THE LOW-LEVEL CENTER.
TC 08P HAS LOST ITS DEEP CONVECTIVE COVER OVER THE PAST TWELVE
HOURS DUE TO INCREASING WESTERLY VERTICAL WIND SHEAR, WHICH IS
CURRENTLY ASSESSED AT 20-25 KNOTS. SIMULTANEOUSLY, THE SYSTEM HAS
STARTED TO EXHIBIT SUBTROPICAL CHARACTERISTICS AND IS EXPECTED TO
COMPLETE SUBTROPICAL TRANSITION WHILE DISSIPATING OVER THE NEXT
12 HOURS. THE REMNANT LOW LEVEL CIRCULATION WILL SPIN DOWN STEADILY
AS IT MEANDERS EASTWARD AND POLEWARD BEYOND THE FORECAST PERIOD AND
ENCOUNTERS CONDITIONS THAT ARE UNFAVORABLE FOR REDEVELOPMENT. THIS
IS THE FINAL WARNING ON THIS SYSTEM BY THE JOINT TYPHOON WRNCEN PEARL
HARBOR HI. THE SYSTEM WILL BE CLOSELY MONITORED FOR SIGNS OF
REGENERATION. MINIMUM CENTRAL PRESSURE AT 120000Z IS 997 MB.
MAXIMUM SIGNIFICANT WAVE HEIGHT AT 120000Z IS 12 FEET.
//
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WDPS31 PGTW 111500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 08P (PITA) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.9S 161.5W
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 104 NM WEST-SOUTHWEST OF RAROTONGA
   MOVEMENT PAST 6 HOURS: EASTWARD AT 26 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
CONVECTION BLOWN POLEWARD AND EASTWARD OF THE SHALLOW LOW-LEVEL
CIRCULATION CENTER (LLCC). CLEAR SKIES LIE TO THE SOUTHWEST OF
TROPICAL CYCLONE (TC) 08P, WHICH IS INDICATIVE OF THE DRY AIR
IMPINGING ON THE CIRCULATION CENTER. THE INITIAL POSITION IS PLACED
WITH LOW CONFIDENCE BASED ON THE OBSCURED AND DIFFICULT-TO-IDENTIFY
LLCC IN THE AFOREMENTIONED ANIMATED EIR. THE INITIAL INTENSITY OF
35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EARLIER
110816Z METOP-C ASCAT IMAGE REVEALING 30-35KT WINDS IN THE
NORTHEASTERN PERIPHERY OF THE LLCC.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: ON THE SOUTHWESTERN PERIPHERY OF A NEAR
EQUATORIAL RIDGE (NER) TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 35 KTS AT 111140Z
   CIMSS AIDT: 35 KTS AT 111210Z
   CIMSS D-MINT: 47 KTS AT 111142Z
   CIMSS D-PRINT: 48 KTS AT 111240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG EASTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST IS 24 HOURS SHORTER THAN
THE PREVIOUS WARNING DUE TO THE RAPIDLY DEGRADING NATURE OF TC 08P
AS ENHANCED UPPER-LEVEL WESTERLIES AND DRY AIR HAVE FURTHER ERODED
THE STRUCTURE OF THE SYSTEM.

FORECAST DISCUSSION: TC 08P WILL CONTINUE TO TRACK
EAST-SOUTHEASTWARD FOR THE REMAINDER OF THE FORECAST PERIOD WHILE
DRIVEN BY THE DEEP-LAYER RIDGE TO THE NORTHWEST AND ENHANCED BY A
DEEP-LAYER TROUGH TO THE SOUTH. THE NEARBY JET TO THE SOUTHWEST
WILL CONTINUE TO INDUCE SUBTROPICAL TRANSITION AS TC 08P BECOMES
FURTHER EMBEDDED WITHIN THE JET MAXIMUM. DRY AIR WILL CONTINUE TO
ENTRAIN INTO THE SYSTEM FOR THE REMAINDER OF THE FORECAST, LEADING
TO GRADUAL WEAKENING BELOW 35KTS AS SUBTROPICAL TRANSITION
COMPLETES.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL TRACK EAST-SOUTHEASTWARD FOR THE REMAINDER OF
THE FORECAST PERIOD. THE CROSS-TRACK SPREAD BY TAU 36 IS 75NM. THE
JTWC INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL
GRADUALLY WEAKEN FOR THE REMAINDER OF THE FORECAST PERIOD. SOME
MULTI-MODEL CONSENSUS MEMBERS WEAKEN THE SYSTEM RAPIDLY,
SPECIFICALLY COAMPS-TC AND HAFS-A, WHILE OTHER MEMBERS SHOW EITHER
GRADUAL WEAKENING OR AN OVERALL STAGNATION OF THE INTENSITY FOR THE
FIRST 12 HOURS. 

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