WDPS31 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 03P (RUBY) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0S 159.7E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 474 NM NORTHWEST OF NOUMEA, NEW CALEDONIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A VERY
COMPACT TROPICAL CYCLONE WHICH HAS OVER THE PAST SIX HOURS, BECOME
INCREASINGLY DISORGANIZED CONVECTIVELY. CLOUD TOPS HAVE BEEN
STEADILY WARMING, ESPECIALLY OVER THE PREVIOUS THREE HOURS, WITH
THE COLDEST TOPS NOW DISPLACED DOWNSHEAR TO THE SOUTHEAST OF THE
ASSESSED CENTER. THE INITIAL POSITION IS ASSESSED WITH ONLY MEDIUM
CONFIDENCE, AS THE LOW LEVEL CIRCULATION CENTER (LLCC) IS CURRENTLY
OBSCURED BY THE CONVECTIVE ACTIVITY AND THERE HAS BEEN NO RECENT
MICROWAVE OR SCATTEROMETER DATA TO ASSIST WITH ANALYSIS OF THE LOW
LEVEL STRUCTURE. MODEL CROSS-SECTIONS SUGGEST THE PRESENCE OF A
PULSE OF MID-LEVEL DRY AIR, WHICH IS IMPINGING THE CORE FROM THE
WEST, AS SUGGESTED BY A FIELD OF STRATOCUMULUS SEEN IN THE MSI AND
EROSION AND WARMING OF THE CLOUD TOPS ON THE NORTHWEST SIDE OF THE
CIRCULATION. THE CROSS-SECTIONS ALSO SHOW A MODERATE AMOUNT OF
DOWNSHEAR TILT TO THE VORTEX. THE INITIAL INTENSITY OF 70 KNOTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN OVERALL AVERAGE OF
AGENCY SUBJECTIVE AND AUTOMATED OBJECTIVE DVORAK INTENSITY
ESTIMATES. OVERALL THE ENVIRONMENT REMAINS FAVORABLE FOR
DEVELOPMENT, BUT HAS BECOME LESS SO SINCE THE PREVIOUS FORECAST,
WITH THE AFOREMENTIONED WEDGE OF MID-LEVEL DRY AIR AND VORTEX TILT
SERVING TO SLOW THE INTENSIFICATION TREND.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   ABRF: T4.0 - 65 KTS
   CIMSS SATCON: 68 KTS AT 122320Z
   CIMSS ADT: 74 KTS AT 122340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR ENTRAINMENT AND DOWNSHEAR
VORTEX TILT.

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING. THE FORECAST DURATION HAS
BEEN TRUNCATED TO 72 HOURS. 

FORECAST DISCUSSION: NO SIGNIFICANT CHANGES ARE EXPECTED IN THE
FORECAST TRACK, AND THE SYSTEM IS FORECAST TO TRACK SOUTHEASTWARD
ALONG THE WESTERN GRADIENT BETWEEN THE DEEP STR TO THE EAST AND A
HIGH-AMPLITUDE TROUGH TO THE WEST. THE CENTER OF TC 03P IS FORECAST
TO TRACK JUST EAST OF NEW CALEDONIA BETWEEN TAU 24 AND 36, THEN
ACCELERATE SOUTHEASTWARD INTO THE OPEN WATERS NORTH OF NEW ZEALAND
THROUGH THE REMAINDER OF THE FORECAST PERIOD. AS DISCUSSED IN
PARAGRAPH TWO ABOVE, A WEDGE OF RELATIVELY DRY MID-LEVEL AIR HAS
BEGUN TO PUNCH IN TOWARDS THE CORE OF THE SYSTEM FROM THE WEST,
DISRUPTING THE MAINTENANCE OF THE CONVECTIVE CORE. OVER THE NEXT 24
HOURS VWS, DRY AIR AND ROBUST POLEWARD OUTFLOW WILL COMPETE AND
OFFSET EACH OTHER, AND THUS, WHILE THE SYSTEM IS EXPECTED TO
CONTINUE TO STRENGTHEN THROUGH TAU 24,THE PEAK INTENSITY HAS BEEN
LOWERED TO 80 KNOTS. AS THE SYSTEM PASSES NEW CALEDONIA THE SYSTEM
IS FORECAST TO BEGIN TO WEAKEN AS SHEAR STEADILY INCREASES AND
ESTABLISHES DOMINANCE OVER THE ROBUST POLEWARD OUTFLOW, SSTS COOL
AND DRY AIR BEGINS TO SMOTHER THE CORE. BY TAU 48 TC 03P BEGINS TO
INTERACT WITH THE STRONG MID-LATITUDE WESTERLIES ALOFT AND BEGIN
SUBTROPICAL TRANSITION, WITH FULL TRANSITION TO A STORM-FORCE
SUBTROPICAL LOW NO LATER THAN TAU 72.  

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN GOOD AGREEMENT THROUGH
TAU 48, THROUGH ALONG-TRACK SPREAD INCREASES AFTER THIS POINT AS
THE SYSTEM MOVES THROUGH THE SUBTROPICAL TRANSITION. THE JTWC
FORECAST LIES ON THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE AND
MOST CLOSELY TRACKS THE GFS SOLUTION, THROUGH THE FORECAST PERIOD.
CONFIDENCE IS HIGH THROUGH TAU 36, DECREASING TO MEDIUM THEREAFTER.
INTENSITY GUIDANCE HAS SHIFTED SIGNIFICANTLY LOWER SINCE THE
PREVIOUS RUN, WITH ALL BUT THE GFS SHIPS AND HWRF SUGGESTING
WEAKENING FROM TAU 00. THE SHIPS GUIDANCE IS THE ONLY MODEL
INDICATING SIGNIFICANT INTENSIFICATION AT THIS TIME. THE JTWC
FORECAST CLOSELY TRACKS THE SHIPS GUIDANCE, AND IS APPROXIMATELY 15
KNOTS HIGHER THAN THE CONSENSUS MEAN THROUGH TAU 36 AND THEN
REJOINS THE MEAN THEREAFTER. IN LIGHT OF THE SIGNIFICANT RUN TO RUN
VARIABILITY AND UNCERTAINTY IN THE INTENSITY GUIDANCE, THERE IS LOW
CONFIDENCE IN THE JTWC FORECAST. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: LOW//
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