WDPN31 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR 
042//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.6N 151.4E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 248 NM NORTHWEST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 20 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 04W (SINLAKU) CONTINUES TOO STEADILY BUT SLOWLY
WEAKEN AS IT TRAVERSES POLEWARD AND BEGINS TO LOSE TROPICAL
CHARACTERISTICS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS A PARTIALLY EXPOSED, AND BROAD LOW LEVEL CIRCULATION CENTER
(LLCC). A LARGE REGION OF MODERATE CONVECTION, AND UPPER-LEVEL
CLOUDS FORMS A DEVELOPING DELTA RAIN REGION IN THE NORTHEASTERN 
QUADRANT OF THE CIRCULATION, INDICATIVE OF THE EARLY PHASES OF EXTRA-
TROPICAL TRANSITION. ALONG THE WESTERN FLANK, STABLE STRATIFORM 
CLOUDS ARE BEING ADVECTED AROUND THE SOUTHERN FLANK AND INTO THE CORE 
VORTEX. THE LATEST CIMSS SHEAR ANALYSIS INDICATES A SUBTLE SHIFT IN 
THE SHEAR DIRECTION FROM WESTERLY TO SOUTHWESTERLY, WHICH ALIGNS THE 
SHEAR VECTOR ALONG THE TRACK. THIS CONGRUENCE LIKELY DELAYS FULL LLCC 
EXPOSURE, SUSTAINING WEAK TO MODERATE CONVECTION IN THE NORTHEASTERN 
QUADRANT. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED 
ON THE ANIMATED MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM 
CONFIDENCE, HEDGED HIGHER THAN THE OBJECTIVE ESTIMATES NOTED BELOW IN
DEFERENCE TO RECENT SAR AND SCATTEROMETER DATA INDICATING A STRONGER
WIND FIELD. THE SYSTEM IS NOW OVER VERY COOL WATERS, EXPERIENCING 
SIGNIFICANT SHEAR AND ENGULFED IN DRY AIR. POLEWARD OUTFLOW, WHILE 
ROBUST, IS INSUFFICIENT TO OFFSET THE OTHERWISE UNFAVORABLE 
ENVIRONMENT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A LOW- TO
MID-LEVEL RIDGE COMPLEX WHICH EXTENDS FROM NEAR GUAM TO SOUTH OF
THE ALEUTIANS. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   CIMSS SATCON: 39 KTS AT 190336Z
   CIMSS ADT: 25 KTS AT 190530Z
   CIMSS AIDT: 33 KTS AT 190530Z
   CIMSS D-MINT: 34 KTS AT 190541Z
   CIMSS D-PRINT: 33 KTS AT 190600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 21-22 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR OVERLAYING THE CIRCULATION. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN TRUNCATED TO 24
HOURS. 

FORECAST DISCUSSION: ANALYSIS OF 1000-500MB THICKNESS, 500MB HEIGHTS, 
850MB WINDS, SST DATA, AS WELL AS MANUAL AND AUTOMATED PHASE 
CLASSIFICATION WORKSHEETS INDICATE TS 04W IS LIKELY A SUBTROPICAL 
CYCLONE AT THIS POINT IN TIME; AT BEST A HYBRID TYPE SYSTEM, 
CHARACTERIZED BY A HYBRID THERMAL STRUCTURE WITH A STRONG MID-LEVEL 
WARM CORE AND SHALLOW VORTEX, MOVING OVER VERY COOL WATERS AND 
FORMATIVE THERMAL ADVECTION. THIS PHASE OF THE SYSTEMS LIFE CYCLE 
WILL BE SHORT-LIVED HOWEVER AND EXTRA-TROPICAL TRANSITION (ETT) WILL 
BEGIN IMMINENTLY. THE SYSTEM IS ACCELERATING NORTHEASTWARD ALONG THE 
NORTHWESTERN FLANK OF A SOUTHWEST-NORTHEAST ORIENTED RIDGE WHICH 
EXTENDS FROM NEAR GUAM TO SOUTH OF THE ALEUTIAN ISLANDS. THE WESTERN 
END OF A OLD FRONTAL BOUNDARY IS SITUATED JUST NORTHEAST OF THE LLCC 
AND EXTENDS FAR TO THE EAST. THE NORTHEASTERN PERIPHERY OF THE 
CIRCULATION IS ALREADY INTERACTING WITH THE BAROCLINIC ZONE, WITH 
ISENTROPIC UPGLIDE FORMING THE DELTA RAIN REGION ALONG THE DEVELOPING 
WARM FRONT. OVER THE NEXT 24 HOURS, THE RIDGE WILL SLOWLY FLATTEN OUT 
TO A MORE EAST-WEST ORIENTATION, WHILE THE FRONTAL BOUNDARY WILL 
BEGIN TO EXERT MORE INFLUENCE, DRIVING TS 04W EASTWARD ALONG THE 
BOUNDARY. TS 04W WILL RAPIDLY COMPLETE ET WITHIN THE NEXT 24 TO 30 
HOURS AS IT COUPLES WITH THE BAROCLINIC ZONE, INCREASES THERMAL 
ADVECTION, AND INTERACTS WITH THE RIGHT ENTRANCE REGION OF THE POLAR 
FRONT JET (PFJ). SYNOPTIC-SCALE DIVERGENCE ASSOCIATED WITH THE PFJ 
JET STREAK MAY PROVIDE FOR TEMPORARY BAROCLINIC RE-INTENSIFICATION 
DURING THE ET PROCESS.

MODEL DISCUSSION: TRACK GUIDANCE IS IN TIGHT CONVERGENCE, WITH 
MINIMAL CROSS- OR ALONG-TRACK SPREAD THROUGH THE SHORT FORECAST 
PERIOD. THE JTWC FORECAST IS ALIGNED WITH THE CONSENSUS (CONW) MEAN 
WITH HIGH CONFIDENCE. INTENSITY GUIDANCE REMAINS BIFURCATED, WITH 
SHIPS AND COAMPS-TC (NAVGEM) INDICATING PRECIPITOUS WEAKENING, WHILE 
THE HAFS-A, HWRF, COAMPS-TC (GFS) AND GFS DEPICT A MORE CONSERVATIVE 
SLOW BUT STEADY WEAKENING SCENARIO. THE JTWC FORECAST IS CONSISTENT 
WITH THE HWRF-BASED DECAY RATE WITH HIGH CONFIDENCE.

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