WDPN31 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.2N 151.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 496 NM SOUTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 04W (SINLAKU) CONTINUING TO ORGANIZE OVER THE PAST 6
HOURS WITH DEEP CONVECTION COLLOCATED WITH THE LOW-LEVEL
CIRCULATION CENTER. CONVECTIVE BANDING NOW ENCOMPASSES A BROAD AREA
SURROUNDING THE CENTER AND HAS BEGUN TO DEVELOP ON THE EASTERN
SIDE. A 092313Z METOP-C ASCAT PASS REVEALED THE LOCATION OF THE
LLCC AND A FIELD OF 35-40KT WINDS NORTH OF THE CENTER. THE INITIAL
POSITION AND INTENSITY ARE BOTH ASSESSED WITH HIGH CONFIDENCE BASED
ON THE AFOREMENTIONED ASCAT DATA. ANALYSIS OF THE ENVIRONMENT
INDICATES THAT FAVORABLE CONDITIONS FOR INTENSIFICATION PERSIST.
HIGH SEA SURFACE TEMPERATURES, ABUNDANT MID-LEVEL MOISTURE, AND
MODERATE POLEWARD OUTFLOW ALOFT ARE ONLY SLIGHTLY OFFSET BY
MODERATE (15-20KT) MID-UPPER LEVEL (250-600 MB) SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT WITH A
SUBTROPICAL RIDGE (STR) POSITIONED NEAR LUZON AND A NEAR-EQUATORIAL
RIDGE (NER) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 41 KTS AT 100010Z
   CIMSS AIDT: 36 KTS AT 100010Z
   CIMSS D-MINT: 33 KTS AT 092209Z
   CIMSS D-PRINT: 38 KTS AT 100010Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 04W IS FORECAST TO CONTINUE ON A SLOW
WESTWARD TRACK THROUGH TAU 30, THEN ACCELERATE NORTHWESTWARD TOWARD
THE MARIANAS ISLANDS FOR THE REMAINDER OF THE FORECAST PERIOD. THE
CONTINUED SLOW SPEED OF ADVANCE IN THE NEAR TERM INCREASES THE
LIKELIHOOD THAT A BUILDING NEAR-EQUATORIAL RIDGE TO THE EAST WILL
DOMINATE THE STEERING FLOW AFTER TAU 36, CAUSING THE NORTHWESTWARD
TURN AND ACCELERATION. THERE IS STILL UNCERTAINTY ABOUT HOW MUCH
INFLUENCE A SUBTROPICAL RIDGE, CENTERED TO THE WEST NEAR LUZON,
WILL HAVE ON THE SYSTEM TRACK FROM TAU 36 ONWARD. THE COMPETING
STEERING SCENARIO CONTINUES TO INTRODUCE UNCERTAINTY IN THE LONG
TERM TRACK OF 04W AND THE JTWC FORECAST HAS AGAIN SHIFTED SLIGHTLY
NORTHWARD TOWARD GUAM. 04 IS CURRENTLY FORECAST TO PASS DIRECTLY
OVER THE ISLAND AROUND 140400Z, THOUGH THERE REMAINS VARIATION TO
THE TRAJECTORY. STEADY INTENSIFICATION IF FORECAST THROUGH TAU 72,
AFTER WHICH THE SYSTEM IS EXPECTED TO MAINTAIN AN INTENSITY OF 105
KTS. THE ENVIRONMENT DURING THE INTENSIFICATION PHASE WILL BE
FAVORABLE, WITH HIGH SEA SURFACE TEMPERATURES, AMPLE MID-LEVEL
MOISTURE, AND GOOD OUTFLOW ALOFT. MODERATE MID-UPPER LEVEL SHEAR IS
THE ONLY FACTOR THAT HAS THE POTENTIAL TO LIMIT THE RATE OF
INTENSIFICATION, AT LEAST THROUGH TAU 96. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE GENERALLY AGREES
ON VERY SLOW MOVEMENT THROUGH TAU 36. GFS CONTINUES TO BE THE
FASTEST MODEL AND HAS NOT BEEN INITIALIZING THE POSITION
WELL, CAUSING THERE TO BE LESS CONFIDENCE IN ITS DEPICTION. THE
ECMWF HAS BEEN INITIALIZING MORE ACCURATELY AND THE ECMWF ENSEMBLE
MEAN TRACKS THE SYSTEM JUST SOUTH OF GUAM. OVERALL, THERE ENDS UP
BEING TWO DISTINCT GROUPINGS AFTER TAU 36. THE FIRST GROUP INCLUDES
THE GOOGLE DEEPMIND ENSEMBLE MEAN, THE EC-AIFS, GALWEM, AND UKMET,
WHICH SHOW A TRACK THAT PASSES CLOSER TO TINIAN AND SAIPAN. THE SECOND 
GROUPING IS COMPRISED OF THE GFS AND ECMWF (AND THEIR ENSEMBLE MEANS), 
WHICH TRACK THE VORTEX TO THE SOUTH OF GUAM. AS A RESULT, CROSS-TRACK 
SPREAD AT TAU 72 IS 260 NM WHICH OPEN UP TO 430 NM AT TAU 120. THE 
JTWC TRACK FORECAST IS PLACED ON THE NORTHERN EDGE OF THE SECOND 
GROUPING, CLOSE TO THE ECMWF ENSEMBLE MEAN WITH LOW CONFIDENCE. 
INTENSITY GUIDANCE AGREES ON INTENSIFICATION THROUGH TAU 96 AND THEN 
LEVELING OFF THROUGH TAU 120. MULTIPLE RAPID INTENSIFICATION (RI) AIDS 
HAVE TRIGGERED THIS MODEL RUN, ADDING UNCERTAINTY TO THE RATE OF 
INTENSIFICATION THROUGH THE APPROACH TO THE MARIANAS. HAFS-A REMAINS 
FAR AND AWAY THE MOST AGGRESSIVE MODEL, SUGGESTING A PEAK INTENSITY OF 
OVER 135 KTS AT TAU 72. THE JTWC INTENSITY FORECAST IS PLACED NEAR THE
MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE. 

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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