WDPN31 PGTW 102100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.0N 151.0E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 61 NM WEST-NORTHWEST OF CHUUK
   MOVEMENT PAST 6 HOURS: EASTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
QUICKLY CONSOLIDATING STORM WITH A RADIALLY EXPANDING CENTRAL DENSE
OVERCAST (CDO). GRAVITY WAVES PROPAGATE OUTWARD WITHIN THE EASTERN
SEMICIRCLE AS THE SYSTEM OVERCOMES THE 10-15 KTS OF SOUTHEASTERLY
VERTICAL WIND SHEAR. TROPICAL STORM (TS) 04W REMAINS
QUASI-STATIONARY APPROXIMATELY 60 NM NORTHWEST OF CHUUK, WHERE A
SURFACE OBSERVATION FROM 1830Z MEASURED THE MEAN SEA LEVEL PRESSURE
AT 988.1 MB WITH SUSTAINED SURFACE WINDS OF 19 KTS GUSTING TO 32
KTS. ENVIRONMENTAL ANALYSIS REVEALS A HIGHLY FAVORABLE ENVIRONMENT
FOR CONTINUED INTENSIFICATION, CHARACTERIZED BY LOW (10-15 KTS)
VERTICAL WIND SHEAR, HIGH (28-29 C) SEA SURFACE TEMPERATURES, AND A
ROBUST POLEWARD OUTFLOW CHANNEL SUPPORTED BY A DEEP LAYER TROUGH TO
THE NORTH AND THE NEAR EQUATORIAL RIDGE CENTERED TO THE SOUTHEAST.
THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON THE
AGENCY POSITION FIXES AND LOW LEVEL CLOUD TRACING IN ANIMATED EIR.
THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY SUBJECTIVE DVORAK FIXES LISTED BELOW AND THE
CIMSS AUTOMATED INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT WITH A
NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTHEAST AND A STRONG
SUBTROPICAL RIDGE (STR) TO THE NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 61 KTS AT 101700Z
   CIMSS ADT: 57 KTS AT 101900Z
   CIMSS AIDT: 51 KTS AT 101900Z
   CIMSS D-PRINT: 74 KTS AT 101900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TS 04W (SINLAKU) REMAINS IN A WEAK STEERING
ENVIRONMENT, TRAPPED BETWEEN THE NER TO ITS SOUTHEAST AND THE STR
CENTERED TO THE NORTHWEST.  THE RESULTING QUASI-STATIONARY PERIOD
MAY INDUCE ERRATIC MOTION WHICH IS UNABLE TO BE REFLECTED ON THE
JTWC TRACK FORECAST. BY TAU 12, HOWEVER, 04W IS EXPECTED TO HAVE
DRIFTED GENERALLY NORTHWARD AS THE NER BUILDS AN EXTENSION ORIENTED
TO THE NORTHWEST. THE EXTENSION WILL CONTINUE TO BUILD WHILE THE
STR CURRENTLY CENTERED OVER THE PHILIPPINES SHIFTS WESTWARD OVER
THE SOUTH CHINA SEA. AS THE NER EXTENSION TAKES OVER AS THE PRIMARY
STEERING RIDGE AROUND TAU 24, SINLAKU IS EXPECTED TO ACCELERATE AND
TRACK NORTHWESTWARD FOR THE DURATION OF THE FORECAST PERIOD. 04W IS
FORECAST TO IMPACT GUAM BETWEEN TAU 72-96 AT AN INTENSITY OF 115
KTS, WITH THE JTWC TRACK FORECAST CONSISTENTLY REMAINING DIRECTLY
OVER OR JUST SOUTH OF THE ISLAND. THE STORM IS PHYSICALLY LARGE,
WITH AN EXPANSIVE ELEVATED WINDFIELD THAT IS EXPECTED TO PERSIST
FOR THE DURATION OF THE FORECAST. SINLAKU IS FORECAST TO STEADILY
INTENSIFY THROUGH TAU 12, FOLLOWED BY A RAPID INTENSIFICATION
PERIOD FROM TAU 12 TO TAU 36. 04W IS EXPECTED TO FURTHER INTENSIFY
FROM TAU 36 TO TAU 48, WITH THE PEAK EXPECTED TO BE 115 KTS AT TAU
48-72. A PEAK INTENSITY HIGHER THAN 115 KTS MAY OCCUR AROUND TAU 60
AND IS UNABLE TO BE REFLECTED IN THE JTWC INTENSITY FORECAST. THE
ENVIRONMENT IS ANTICIPATED TO REMAIN HIGHLY FAVORABLE THROUGHOUT
THE DURATION OF THE FORECAST PERIOD, ALLOWING UNINHIBITED
INTENSIFICATION FOR THE TIME BEING. INTERACTION WITH THE ISLAND IS
NOT EXPECTED TO HAVE A SIGNIFICANT IMPACT ON THE STORM'S INTENSITY,
WHICH IS FORECAST TO REMAIN RELATIVELY STEADY THROUGH TAU 120. 

MODEL DISCUSSION: DETERMINISTIC TRACK MODEL GUIDANCE IS IN MODERATE
AGREEMENT IN TRACK THROUGH TAU 72, WITH ALL MODELS IN AGREEMENT
THAT 04W WILL TRACK GENERALLY NORTHWESTWARD ALONG THE NER
EXTENSION. UNCERTAINTY ARISES IN THE LATE-TERM FORECAST, WITH A 500
NM CROSS-TRACK SPREAD OCCURRING BY TAU 120. NOTABLY, THERE IS A
SPLIT BETWEEN THE PHYSICS-BASED GLOBAL MODELS AND THE EXPERIMENTAL
AI-BASED MODELS; ECMWF, GFS, AND NAVGEM ALL DEPICT A TRACK TO THE
SOUTH OF OR OVER GUAM, WHILE EXPERIMENTAL GOOGLE DEEPMIND, THE
ECMWF AI MODEL, AND WINDBORNE WEATHERMESH MODEL ALL DEPICT A TRACK
NORTH OF GUAM. THE GROUPING OF SEVERAL MODELS IN THE CENTER OF THE
ENVELOPE ALL INDICATE A PATH EXTREMELY CLOSE TO GUAM. THE JTWC
TRACK FORECAST IS PLACED NEAR THE MULTIMODEL CONSENSUS WITH OVERALL
LOW CONFIDENCE. RELIABLE INTENSITY GUIDANCE IS IN GOOD AGREEMENT IN
THE RATE OF INTENSIFICATION THROUGH TAU 36-48, WITH MESOSCALE
MODELS AND RAPID INTENSIFICATION AIDS SUGGESTING A PERIOD OF RAPID
INTENSIFICATION BEGINNING AROUND TAU 12 AND CONTINUING THROUGH TAU
36. INTENSITY MODELS ARE IN POOR AGREEMENT ON PEAK INTENSITY, WITH
MODELS RANGING FROM 100 KTS TO 130 KTS BETWEEN TAU 48-72. THE JTWC
INTENSITY FORECAST IS ASSESSED OVERALL MEDIUM CONFIDENCE AND LIES
CLOSE TO THE MULTIMODEL CONSENSUS. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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