WDPS31 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 06P (SIX) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.9S 149.7W
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 216 NM NORTH OF PAPEETE, TAHITI
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 20 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 06S (SIX) HAS RAPIDLY CONSOLIDATED AND
INTENSIFIED OVER THE LAST 24 HOURS, EMBEDDED WITHIN THE SOUTH
PACIFIC CONVERGENCE ZONE (SPCZ) WHICH EXTENDS SOUTH TO NEAR
SUBTROPICAL STORM (SS) 99P. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS AN EXTREMELY COMPACT LOW LEVEL CIRCULATION
CENTER (LLCC), OBSCURED BY DEEP, PERSISTENT CONVECTION. A 042032Z
GMI 37GHZ MICROWAVE IMAGE REVEALED A WELL-DEFINED LLCC, WITH A TINY
LOW EMISSIVITY REGION (LER) OUTLINING THE COMPACT INNER-CORE, AND A
STRONG BAND OF CONVECTION EXTENDING IN A BROAD ARC FORMING INTO A
SHRIMP-LIKE SHAPE TYPICAL OF DEVELOPING TROPICAL CYCLONES. A
041921Z ASCAT-B BULLSEYE REVEALED A VERY SMALL CORE OF ENHANCED
WINDS UP TO 30 KNOTS, ALTHOUGH THE EXTREMELY COMPACT STRUCTURE
LIKELY PRECLUDED DETECTION OF POTENTIALLY HIGHER WINDS WITHIN THE
INNER-CORE. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON AN EXTRAPOLATION OF THE GMI IMAGE DISCUSSED ABOVE, AND
NEAR THE PGTW FIX POSITION BASED ON THE MSI. THE INITIAL INTENSITY
IS ASSESSED WITH MEDIUM CONFIDENCE DUE TO THE BROAD DISAGREEMENT
BETWEEN THE PGTW AND KNES DVORAK CURRENT INTENSITY ESTIMATES, AND
EXTRAPOLATION OF THE EARLIER ASCAT DATA. ENVIRONMENTAL CONDITIONS
ARE MARGINALLY FAVORABLE, WITH LOW WIND SHEAR, STRONG POLEWARD
OUTFLOW ALOFT AND WARM SSTS. OUTFLOW IS BEING ENHANCED BY THE
PRESENCE OF A VERY DEEP 200MB TROF SITUATED TO THE WEST.

INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SCATTEROMETER
DATA. 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST-NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T1.0 - 25 KTS
   PHFO: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SYSTEM IS EMBEDDED ALONG THE SOUTH PACIFIC
CONVERGENCE ZONE (SPCZ). DRY MID-LEVEL AIR TO THE WEST-SOUTHWEST. 

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: JUST AS IT FORMED VERY RAPIDLY, TC 06P WILL BE
AN EQUALLY SHORT-LIVED TC. THE SYSTEM WILL RACE OFF TO THE
SOUTHEAST THROUGH THE ENTIRE FORECAST PERIOD, ALONG THE A STRONG
STEERING GRADIENT BETWEEN THE WESTERN FLANK OF A DEEP STR TO THE
EAST AND THE DEEP UPPER-LEVEL TROF LURKING OUT TO THE WEST.
GENERALLY FAVORABLE CONDITIONS ARE EXPECTED TO PERSIST FOR THE NEXT
24 HOURS, WHICH WILL ALLOW THE SYSTEM TO INTENSIFY UP TO 40
KNOTS, POTENTIALLY A FEW KNOTS HIGHER BY TAU 24. BY THAT POINT
HOWEVER, THE SYSTEM WILL MOVE UNDER A 300MB JET STREAK, BE ENGULFED
BY VERY DRY MID-LEVEL AIR AND MOVE OVER MUCH COOLER SSTS (24-25C)
AND BEGIN A VERY RAPID SUBTROPICAL TRANSITION (STT). STT IS
EXPECTED TO BE COMPLETE NO LATER THAN TAU 36, AS THE SYSTEM RACES
POLEWARD IN THE WAKE OF 99P. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
VERY TIGHT AGREEMENT, WITH MINIMAL CROSS-TRACK SPREAD AND MARGINAL
ALONG-TRACK SPREAD. THE JTWC FORECAST IS POSITIONED CLOSE TO THE
GFS DETERMINISTIC TRACKER WITH HIGH CONFIDENCE. INTENSITY GUIDANCE
IS ALSO IN GOOD AGREEMENT, WITH ALL MODELS SHOWING A PEAK INTENSITY
BETWEEN 40-45 KNOTS BY TAU 12, FOLLOWED BY A SLOW WEAKENING
BEGINNING AT TAU 24. THE JTWC FORECAST IS PLACED NEAR THE CONSENSUS
MEAN WITH HIGH CONFIDENCE. 

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