WDPS31 PGTW 151500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 08P (EIGHT) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.8S 171.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 241 NM NORTHEAST OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT, ASYMMETRIC SYSTEM, WITH AN ELONGATED REGION OF PERSISTENT,
BUT NOW WEAKENING, CONVECTION TO THE EAST OF THE ASSESSED LOW LEVEL
CIRCULATION CENTER (LLCC). A VERY SMALL REGION OF DEVELOPING
CONVECTION APPEARS TO BE DEVELOPING NEAR THE ASSESSED CENTER BUT IT
REMAINS TO BE SEEN IF THIS WILL PERSIST. A 150930Z ASCAT-B PASS
REVEALED A VERY SMALL LLCC AND A HIGHLY ASYMMETRIC WIND FIELD, WITH
30-35 KNOT WINDS RESTRICTED TO AN ARC ON THE EASTERN FLANK OF THE
CIRCULATION. THE ACCOMPANYING MHS 89GHZ MICROWAVE IMAGE REVEALED A
DISORGANIZED AREA OF CONVECTION DISPLACED TO THE EAST OF THE LLCC,
WHICH BASED ON THE LATEST EIR IMAGERY APPEARS TO BE STRETCHING OUT
ALONG A NORTHWEST-SOUTHEAST AXIS. THE INITIAL POSITION IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON AN EXTRAPOLATION OF THE LLCC SEEN
IN THE SCATTEROMETER PASS. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON A BLEND OF THE OBJECTIVE AND SUBJECTIVE
INTENSITY ESTIMATES NOTED BELOW. THE ENVIRONMENT REMAINS MARGINALLY
FAVORABLE, WITH MODERATE NORTHWESTERLY SHEAR OFFSETTING THE STRONG
POLEWARD OUTFLOW AND WARM SSTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
NEAR EQUATORIAL RIDGE (NER) POSITIONED EAST-WEST ALONG THE 10S
LATITUDE LINE. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   PHFO: T3.0 - 45 KTS
   CIMSS ADT: 55 KTS AT 151130Z
   CIMSS AIDT: 42 KTS AT 151200Z
   CIMSS D-MINT: 35 KTS AT 150909Z
   CIMSS D-PRINT: 42 KTS AT 151210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN TRUNCATED TO 72
HOURS. 

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 08P (EIGHT) HAS, AS
EXPECTED, STEADILY TURNED FROM A SOUTHEASTWARD TO A MORE EASTWARD
TRAJECTORY OVER THE COURSE OF THE LAST DAY, AS IT MOVES UNDER THE
BUILDING RIDGE TO THE NORTH. WHILE THE OVERALL TRACK DIRECTION
IS NOT MUCH IN DOUBT IN THE SHORT-TERM, THE SPEED OF ADVANCE IS
VERY MUCH IN DOUBT. TRACK MODELS ARE BROKEN INTO TWO DISTINCT
CAMPS, WITH THE EUROPEAN MODELS (ECMWF, EGRR, ECEPS) DEVELOPING A
VERY WEAK SYSTEM WHICH RESULTS IN A WEAK STEERING GRADIENT AND A
VERY SLOW COURSE TOWARDS THE EAST, ONE WHICH NEVER EVEN REACHES
FIJI. THE U.S. MODELS (GFS, GEFS, AND THE MESOSCALE MODELS) ON THE
OTHER HAND DEVELOP A MUCH STRONGER SYSTEM, WITH A CORRESPONDINGLY
STRONGER STEERING GRADIENT, RESULTING IN A MUCH FASTER EASTWARD
TRACK, WHICH PASS SOUTH OF AMERICAN SAMOA BEFORE TURNING POLEWARD.
A LOT DEPENDS ON HOW THE MODELS ARE INITIALIZING, AND IT APPEARS
THAT NEITHER THE GFS NOR THE ECMWF ARE DOING A GOOD JOB ON THIS
FRONT. THE GFS IS TOO STRONG AND SYMMETRICAL COMPARED TO THE
SCATTEROMETER, WHILE THE ECMWF IS TOO WEAK. WITH SO MUCH
UNCERTAINTY, THE FORECAST IS RELYING ON CONSISTENCY AND
PERSISTENCE, WALKING BACK A BIT FROM THE MORE AGGRESSIVE GFS
SOLUTIONS, BUT ALSO MOVING FAR OUT IN FRONT OF THE EUROPEAN MODEL
SOLUTIONS. IN TERMS OF INTENSITY, AGAIN ITS A TALE OF TWO
COMPLETELY DIFFERENT OUTCOMES. THE EUROPEAN MODELS, BEING SLOWER,
BRING THE SYSTEM UNDER A JET STREAM EARLY IN THE FORECAST, WHICH
KILLS THE SYSTEM WITHIN 24 TO 36 HOURS. IN THE GFS SOLUTION, THIS
PROCESS IS DELAYED UNTIL TAU 36 TO TAU 48. IF THE SYSTEM DOES MOVE
OUT TO THE EAST AS EXPECTED, THEN IT WILL HAVE A SHORT WINDOW OF
MARGINALLY FAVORABLE CONDITIONS, WHERE IT COULD INTENSIFY A BIT,
BEFORE IT IS HAMMERED BY INCREASED SHEAR AND DRY AIR, WHICH WILL
LEAD TO ITS DEMISE BY TAU 72. 

MODEL DISCUSSION: AS BRIEFLY OUTLINED ABOVE, DETERMINISTIC MODELS
ARE SPLIT, WITH ROUGHLY HALF THE CONSENSUS KEEPING THE SYSTEM WEST
OF FIJI THROUGH TAU 72, WHILE THE OTHER HALF TRACKS SOUTH OF
AMERICAN SAMOA BEFORE TURNING POLEWARD AFTER TAU 72. THE JTWC
FORECAST IS CONSISTENT WITH THE GEFS MEAN UNTIL TAU 36, THEN
FOLLOWS THE GEFS DIRECTION BUT LAGS BEHIND BY ABOUT 100NM BY THE
END OF THE FORECAST. CONFIDENCE IS LOW DUE TO THE ALONG-TRACK
BIFURCATION IN THE GUIDANCE. INTENSITY GUIDANCE IS IN BETTER SHAPE,
WITH ALL MODELS IN AGREEMENT THAT THE SYSTEM WILL LIKELY INTENSIFY
BETWEEN 5-15 KNOTS BY TAU 24, THEN STEADILY WEAKEN THEREAFTER. THE
JTWC FORECAST IS PLACED CLOSE TO THE CONSENSUS MEAN THROUGH THE
FORECAST PERIOD, WITH LOW CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: LOW
   INTENSITY 00-72 HR: LOW//
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