WDPN31 PGTW 182100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR 
040//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.3N 148.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 392 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A NEARLY
FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH WEAK
CONVECTION AND MID-LEVEL CLOUDS REMAINING PRIMARILY IN THE EASTERN
SEMICIRCLE. ANIMATED WATER VAPOR IMAGERY DISPLAYS ROBUST POLEWARD
OUTFLOW ASSOCIATED WITH THE ENTRANCE REGION OF A MID-LATITUDE JET
STREAM TO THE NORTHEAST. THE WATER VAPOR IMAGERY ALSO SHOWS A
SIGNIFICANT DRY AND STABLE AIR MASS ENCROACHING FROM THE WEST AND
BEING ENTRAINED INTO THE WEAKENING VORTEX. AN EARLIER 181534Z
AMSR-2 89 GHZ MICROWAVE IMAGE REVEALED LOW-LEVEL CLOUD BANDS
WRAPPING TIGHTLY INTO THE CORE OF THE LLCC. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN EIR
IMAGERY. THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON A STEADY WEAKENING TREND SINCE THE MOST RECENT
181056Z METOP-C ASCAT PASS. DVORAK-BASED INTENSITY ESTIMATES ARE
ALL ANALYZED TO BE UNDERESTIMATING THE CURRENT INTENSITY DUE TO THE
LACK OF CONVECTIVE STRUCTURE. THE ENVIRONMENT IS CHARACTERIZED AS
UNFAVORABLE, WITH LOW (23-24 C) SEA SURFACE TEMPERATURES, HIGH
(25-30 KTS) WESTERLY VERTICAL WIND SHEAR (VWS), AND SIGNIFICANT DRY
AIR ENTRAINMENT.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 49 KTS AT 181720Z
   CIMSS ADT: 30 KTS AT 181800Z
   CIMSS AIDT: 36 KTS AT 181800Z
   CIMSS D-MINT: 44 KTS AT 181623Z
   CIMSS D-PRINT: 43 KTS AT 181800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 23-24 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT ALONG THE WESTERN FLANK

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

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 AS THE STR TO THE SOUTHEAST
REGAINS CONTROL AS THE PRIMARY STEERING INFLUENCE. THE SYSTEM IS
FORECAST TO CONTINUE ACCELERATING WITH AN INCREASINGLY EASTWARD
COMPONENT THROUGH TAU 36 AS THE STR 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 AROUND
TAU 36 WHILE RETAINING AN EXPANSIVE AREA OF GALE-FORCE WINDS. THE
INTENSITY IS FORECAST TO STEADILY DECREASE IN UNFAVORABLE
CONDITIONS THROUGHOUT THE ENTIRE FORECAST PERIOD. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT
WITH THE EAST-NORTHEASTWARD TRAJECTORY OF TS SINLAKU WITH A
CROSS-TRACK SPREAD OF 105 NM AT TAU 36. THERE IS STILL A NOTABLE
UNCERTAINTY WITH THE TRACK SPEED CAUSING A 120 NM ALONG-TRACK
SPREAD. THE GOOGLE DEEPMIND ENSEMBLE MEAN IS THE FASTEST SOLUTION
WHILE JGSM IS THE SLOWEST. THE JTWC TRACK FORECAST IS PLACED CLOSE
TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. ALL INTENSITY
GUIDANCE SUGGESTS A STEADY WEAKENING TREND. THE SHIPS SOLUTIONS
CONTINUE TO DECREASE MUCH FASTER THAN THE REMAINDER OF THE
GUIDANCE. 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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