WDPS31 PGTW 280300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 15P (JUDY) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.0S 168.6E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 223 NM NORTH OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE 15P (JUDY) CONTINUES TO STRUGGLE TO CONSOLIDATE TO
DEVELOP A VERTICALLY ALIGNED VORTEX IN THE FACE OF MODERATE
MID-LEVEL SHEAR. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND
ENHANCED INFRARED (EIR) DEPICTS A CENTRAL COLD COVER (CCC)
OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC), THOUGH THE MOST
RECENT FRAMES OF IMAGERY SUGGEST THAT THE LOW LEVEL CORE MAY BE
TRYING TO CONSOLIDATE EAST OF SOLA ON THE ISLAND OF VANUA LAVA. THE
CCC AND LACK OF RECENT MICROWAVE IMAGERY PRESENTS A SIGNIFICANT
CHALLENGE TO DETERMINATION OF THE INITIAL POSITION, WITH A WIDE
SPREAD IN THE AGENCY FIX POSITIONS. A 280000Z SURFACE OBSERVATION
FROM SOLA SHOWED WINDS FROM 240 AT 16 KNOTS, WHILE OBSERVATIONS
FROM FURTHER SOUTH AT SARAMATA AND LUGANVILLE INDICATED WINDS FROM THE
EAST, SUGGESTING THAT THE LLCC IS AT ROUGHLY THE SAME LATITUDE AS
SOLA, OR APPROXIMATELY 14S. THE EVIDENCE IS THIN HOWEVER, LEADING
TO LOW CONFIDENCE IN THE INITIAL POSITION. THE INITIAL INTENSITY IS
ASSESSED AT 55 KNOTS WITH MEDIUM CONFIDENCE BASED ON THE T3.5 FROM
PHFO AND THE ADT AND SATCON ESTIMATES. THE ENVIRONMENT REMAINS VERY
FAVORABLE WITH WARM (30-31C) SSTS, HIGH OHC (165 KJ PER CM2) AND
STRONG EQUATORWARD OUTFLOW. OVERALL DEEP-LAYER SHEAR REMAINS LOW
(5-10 KTS) BUT HIGH RESOLUTION MODEL DATA SUGGESTS MODERATE TO
STRONG (20-25 KTS) SOUTHERLY SHEAR IN THE MID-LEVELS. THE SATELLITE
DEPICTION AND THE LACK OF CONSOLIDATION OVER THE PAST 12 HOURS,
WITH ALL OTHER FACTORS BEING EQUAL, SUGGESTS THE MID-LEVEL SHEAR
MAY IN FACT BE PRESENT, BUT CANNOT BE CONFIRMED WITHOUT ACTUAL
SOUNDING DATA.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   PHFO: T3.5 - 55 KTS
   NFFN: T4.0 - 65 KTS
   CIMSS SATCON: 55 KTS AT 272048Z
   CIMSS ADT: 55 KTS AT 280030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 15P (JUDY) HAS SLOWED CONSIDERABLY OVER THE
PAST 12 HOURS, AS IT APPROACHES THE SUBTROPICAL RIDGE AXIS TO THE
NORTHEAST OF VANUATU. THE MOTION VECTOR OVER THE PAST SIX HOURS HAS
BEEN A BIT MORE WESTWARD THAN EXPECTED, THOUGH THE HIGH UNCERTAINTY
SURROUNDING THE INITIAL POSITION MEANS THE ACTUAL MOTION VECTOR IS
EQUALLY UNCERTAIN. REGARDLESS, THE SYSTEM SHOULD START TO TURN
SOUTHWARD OVER THE NEXT 12 HOURS OR SO AS IT APPROACHES THE AXIS OF
THE RIDGE. BY TAU 36, IT SHOULD BE AROUND THE AXIS AND ACCELERATING
SOUTHEASTWARD ALONG THE SOUTHWEST PERIPHERY OF THE STEERING RIDGE.
THE SYSTEM IS FORECAST TO TRACK VERY CLOSE TO PORT VILA, VANUATU,
MAKING A CPA OF 20NM OR LESS AROUND 010000Z, THEN TRACKING DOWN THE
REMAINDER OF THE ISLAND GROUP. AS DISCUSSED EARLIER, THE
ENVIRONMENT IS VERY FAVORABLE FOR INTENSIFICATION AND WILL REMAIN
SO FOR THE NEXT 24-36 HOURS, THE ONLY THING HOLDING BACK TC 15P
BEING THE MODERATE MID-LEVEL SHEAR AND LACK OF A CONSOLIDATED
VORTEX. IF THE MODELS ARE CORRECT, THE VORTEX SHOULD BE SOLIDLY
ESTABLISHED WITHIN THE NEXT 12 HOURS, AND THE SYSTEM WILL RAPIDLY
INTENSIFY THROUGH TAU 36, REACHING A PEAK OF 85 KNOTS. THE GOOD
TIMES DONT LAST THOUGH AND BY TAU 48, AN APPROACHING MID-LATITUDE
TROUGH WILL MOVE IN FROM THE WEST, WHICH WHILE PROVIDING
EXCEPTIONALLY GOOD POLEWARD OUTFLOW, WILL ALSO DRAMATICALLY
INCREASE THE SHEAR OVER TC 15P, LIKELY DECAPITATING THE SYSTEM
FAIRLY QUICKLY. THE TROUGH ALOFT ALSO USHERS IN A PUNCH OF DRY
MID-LEVEL AIR, EFFECTIVELY SMOTHERING THE SYSTEM AND THE COMBINED
EFFECTS OF SHEAR AND DRY AIR WILL EFFECTIVELY KILL TC 15P AS A
TROPICAL CYCLONE. RAPID SUBTROPICAL TRANSITION BEGINS JUST AFTER
TAU 48, AND THE SYSTEM WILL TRANSITION TO A STORM-FORCE SUBTROPICAL
LOW NO LATER THAN TAU 96 AND POTENTIALLY AS EARLY AS TAU 72. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE REMAINS
IN GOOD AGREEMENT THROUGH THE FORECAST PERIOD, WITH ONLY MODEST
SPREAD ACROSS THE CONSENSUS MEMBERS. THE BULK OF THE GUIDANCE IS IN
A VERY TIGHT ENVELOPE, ONLY 70NM WIDE AT TAU 72 WHILE THE UKMET,
EGRR AND GALWEM ARE BUNCHED TOGETHER IN THEIR OWN LITTLE GROUP
ABOUT 50NM FURTHER WEST THAN THE OTHER MEMBERS. THE JTWC FORECAST
LIES CLOSE TO THE GFS AND ECMWF SOLUTIONS WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE HAS BACKED OFF A BIT DUE TO THE SLOW
CONSOLIDATION, THOUGH THE RIPA, FRIA AND RI25-RI35 RAPID
INTENSIFICATION (RI) AIDS CONTINUE TO FIRE. THE HWRF HAS ALSO BACK
OFF CONSIDERABLY SINCE THE PREVIOUS RUN, NOW INDICATING A PEAK OF
JUST 70 KNOTS AT TAU 24. THE JTWC FORECAST REMAINS SLIGHTLY ABOVE
THE CONSENSUS MEAN, ABOVE THE HWRF, BUT BELOW THE RI GUIDANCE
THROUGH TAU 36, THEN LIES CLOSE TO THE MEAN THROUGH THE REMAINDER
OF THE FORECAST. CONFIDENCE IS MEDIUM THROUGH THE DURATION OF THE
FORECAST PERIOD. 

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