WDPN31 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W (CHAMPI) WARNING NR 
014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3N 140.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 338 NM SOUTH-SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS CONTINUED
CYCLING CONVECTION, WITH DEEP CONVECTION FLARING UP NEAR THE
ASSESSED CENTER, ONLY TO QUICKLY DISSIPATE, THOUGH THE OVERALL
STRUCTURE HAS IMPROVED OVER THE PREVIOUS 12 HOURS. A 240407Z AMSR2
COLOR 37GHZ MICROWAVE IMAGE SHOWED A WELL DEFINED MICROWAVE EYE
FEATURE, WITH A SOLID BAND OF DEEP CONVECTION SURROUNDING ALL BUT
THE NORTHWEST QUADRANT OF THE CIRCULATION, LENDING HIGH CONFIDENCE
TO THE INITIAL POSITION. THE INITIAL INTENSITY IS ASSESSED AT 45
KNOTS, CONSISTENT WITH MULTI-AGENCY DVORAK INTENSITY ESTIMATES AND
SLIGHTLY HIGHER THAN SUBJECTIVE ESTIMATES. WHILE THE OVERALL SHEAR
VALUES ARE LOW (10-15 KTS), WATER VAPOR IMAGERY AND CIMSS
UPPER-LEVEL WIND ANALYSIS INDICATE SOME MID-LEVEL DRY AIR TO THE
NORTHWEST, ALONG WITH SOME NORTHWESTERLY FLOW ALOFT WHICH ARE
CREATING SOME PRESSURE AND INHIBITING THE CONSOLIDATION OF THE CORE
ON THE NORTHWEST SIDE. HOWEVER THE SYSTEM IS ALSO BEGINNING TO
WEAKLY TAP INTO THE DIVERGENT OUTFLOW ALONG THE SOUTHERN SIDE OF A
TUTT CELL TO THE NORTHEAST AND OVERALL, THE ENVIRONMENT IS
CONDUCIVE TO FURTHER INTENSIFICATION.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 39 KTS AT 240540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM CHAMPI IS EXPECTED TO CONTINUE
TRACKING GENERALLY NORTHWARD, BEFORE ROUNDING THE STR AXIS BY TAU
36 AND THEN AFTER ACCELERATING NORTHEASTWARD. THE SYSTEM IS EXPECTED
TO COMMENCE EXTRATROPICAL TRANSITION (ETT) BEFORE TAU 72 AS IT
BEGINS TO INTERACT WITH THE BAIU BOUNDARY SOUTHEAST OF HONSHU,
MOVES OVER PROGRESSIVELY COOLER WATERS AND INTERACTS WITH A MAJOR
SHORTWAVE TROUGH APPROACHING FROM THE WEST. BY TAU 96, THE SYSTEM
IS EXPECTED TO COMPLETE ETT AS IT BECOMES COMPLETELY ABSORBED INTO
THE BAIU BOUNDARY. THE JTWC INTENSITY FORECAST CALLS FOR SLOW
INTENSIFICATION THROUGH TAU 12 AS THE UPPER-LEVEL OUTFLOW PATTERN
REMAINS RELATIVELY MARGINAL. BY TAU 12 THE PATTERN ALOFT BECOMES
MORE FAVORABLE, WITH THE DEVELOPMENT OF DUAL-CHANNEL OUTFLOW AS THE
SYSTEM LIES UNDER THE SOUTHWESTERN PORTION OF A WEAK 200MB RIDGE.
TS 06W IS FORECAST TO REACH PEAK INTENSITY BETWEEN TAUS 36-48 AS IT
EXPERIENCES A SHORT PERIOD OF STRONG POLEWARD OUTFLOW INTO THE
DIVERGENT AREA AHEAD OF A MAJOR SHORTWAVE TROUGH. THEREAFTER, THE
COMBINATION OF RAPIDLY INCREASING VWS AND DECREASING SSTS NORTH OF
THE 28TH LATITUDE, WILL COMBINE TO INDUCE RAPID WEAKENING THROUGH
THE REMAINDER OF THE FORECAST PERIOD. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN OVERALL GOOD
AGREEMENT WITH ONLY A 75 NM SPREAD THROUGH TAU 48. HOWEVER,
INCREASING ALONG TRACK UNCERTAINTY LEADS TO A 350 NM SPREAD BY TAU
96. THE JTWC FORECAST LIES ON THE RIGHT, OR INSIDE, PORTION OF THE
GUIDANCE ENVELOPE AND SLIGHTLY FASTER THAN THE MULTI-MODEL
CONSENSUS MEAN THROUGH THE DURATION OF THE FORECAST, WITH ONLY THE
GFS DETERMINISTIC SOLUTION BEING FURTHER RIGHT. THE JTWC INTENSITY
FORECAST IS SLIGHTLY LOWER THAN THE MULTI-MODEL CONSENSUS THROUGH
TAU 72, WITH A FAIRLY LARGE SPREAD IN POTENTIAL PEAK INTENSITY, AS
DENOTED BY THE HWRF SOLUTION INDICATING A PEAK OF 90 KTS. BASED ON
THE OVERALL ENVIRONMENT, THE TIMING OF THE ARRIVAL OF SIGNIFICANT
SHEAR AND THE RAPID DROP-OFF OF SSTS, THE HWRF SOLUTION IS
CURRENTLY CONSIDERED TO BE A SIGNIFICANT OUTLIER AND NOT A LIKELY
OUTCOME.  

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