WDPN31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR 
041//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.5N 149.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 455 NM EAST-NORTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A MOSTLY
EXPOSED AND BROADENING LOW-LEVEL CIRCULATION CENTER (LLCC) WITH
SHALLOW CONVECTION PRIMARILY LIMITED TO THE NORTHEASTERN PERIPHERY.
ABUNDANT DRY AIR FROM THE WEST IS EVIDENCED BY BANDS OF
STRATOCUMULUS CLOUDS WRAPPING INTO THE CORE OF THE LLCC AS THE
SYSTEM SLOWLY WEAKENS. A TIMELY 182321Z METOP-C ASCAT PASS REVEALED
THE SLIGHTLY ELONGATED WIND SPEED MINIMUM OF THE LLCC, LENDING HIGH
CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY OF 55 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A FIELD OF 45-50 KTS IN
THE SOUTHEAST AND NORTHWEST QUADRANTS IN THE SAME ASCAT DATA. THE
ENVIRONMENT IS ASSESSED TO BE UNFAVORABLE WITH LOW (22-23 C) SEA
SURFACE TEMPERATURES, HIGH (30-35 KTS) WESTERLY VERTICAL WIND SHEAR
(VWS), AND SIGNIFICANT DRY AIR ENTRAINMENT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS ADT: 25 KTS AT 190000Z
   CIMSS AIDT: 33 KTS AT 190000Z
   CIMSS D-PRINT: 40 KTS AT 190000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30-35 KTS
   SST: 22-23 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT ALONG THE WESTERN FLANK

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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.

FORECAST DISCUSSION: TROPICAL STORM (TS) 04W (SINLAKU) CONTINUED TO
ACCELERATE IN A NORTHEASTWARD DIRECTION UNDER THE STEERING
INFLUENCE OF THE STR TO THE SOUTHEAST, ADVANCING AT A RATE OF 16
KTS OVER THE PAST 6 HOURS. THE SYSTEM IS FORECAST TO CONTINUE
ACCELERATING WITH AN INCREASINGLY EASTWARD COMPONENT THROUGH TAU 36
AS THE STEERING RIDGE MIGRATES SOUTHWESTWARD. EXTRATROPICAL
TRANSITION (ETT) IS EXPECTED TO BEGIN AFTER TAU 12 AS TS SINLAKU
BECOMES EMBEDDED IN THE MID-LATITUDE WESTERLIES AND GAINS
BAROCLINIC FEATURES. ETT IS EXPECTED TO BE COMPLETE BY TAU 36. THE
INTENSITY IS FORECAST TO STEADILY DECREASE DUE TO UNFAVORABLE
CONDITIONS THROUGHOUT THE ENTIRE FORECAST PERIOD, HOWEVER, THE
EXTRATROPICAL LOW IS EXPECTED TO MAINTAIN AN EXPANSIVE AREA OF GALE
FORCE WINDS. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT
WITH THE EAST-NORTHEASTWARD TRAJECTORY OF TS SINLAKU WITH A
CROSS-TRACK SPREAD OF 140 NM AT TAU 36. THERE IS STILL A NOTABLE
UNCERTAINTY WITH THE TRACK SPEED CAUSING A 160 NM ALONG-TRACK
SPREAD. THE GOOGLE DEEPMIND ENSEMBLE MEAN IS THE FASTEST SOLUTION
WHILE JGSM REMAINS THE SLOWEST. THE JTWC TRACK FORECAST IS PLACED
CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. ALL
INTENSITY GUIDANCE SUGGESTS A GRADUAL WEAKENING TREND. THE SHIPS
SOLUTIONS CONTINUE TO DECREASE MUCH FASTER THAN THE REMAINDER OF
THE GUIDANCE, WHICH HAS CAUSED THE CONSENSUS TO BE PULLED DOWN. THE
JTWC INTENSITY FORECAST IS PLACED NEAR THE HAFS-A AND HWRF
SOLUTIONS WITH HIGH CONFIDENCE.

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